NEET Biology Chromosomal Basis Of Inheritance Multiple Choice Question And Answers

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Biology MCQ For NEET With Answers – Chromosomal Basis Of Inheritance

Question 1. The word chromosome simply refers to

  1. Painted body
  2. Coloured body
  3. Doubling body
  4. Thread-like body

Answer:  2. Coloured body

The word chromosome is derived from Chrom-coloured; some- body. Therefore, the meaning of chromosome is the coloured body.

Question 2. Chromosome theory of inheritance was proposed by

  1. Sutton and Boveri
  2. Bateson and Punnett
  3. TH Morgan
  4. Watson and Crick

Answer:  1. Sutton and Boveri

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The chromosomal theory of inheritance proposed by Sutton and Boveri. It states that chromosomes are the vehicles of genetic heredity. Neither Mendelian genetics nor gene linkage is perfectly accurate, instead, chromosome behaviour involves segregation, independent assortment, and occasionally, linkage.

Question 3. Chromosome theory states that

  1. Genes are located on chromosome
  2. Chromosome is made up of DNA
  3. Chromosome is made up of RNA
  4. All of the above

Answer:  1. Genes are located on chromosome

inheritance and variation mcq

Chromosome theory states that genes are located on specific locations on chromosome. According to chromosomal theory of inheritance, the behaviour of chromosomes and its location can explain Mendel’s law of inheritance.

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NEET Biology Chromosomal Basis Of Inheritance Multiple Choice Question And Answers

Question 4. Sometimes chromosome number increases or decreases due to

  1. Mutagenic change
  2. Non-disjunction of chromosome
  3. Genetic repeats
  4. All of the above

Answer:  2. Non-disjunction of chromosome

Sometimes chromosome number increases or decreases due to non-disjunction of chromosome. It refers to condition of failure of homologous chromosomes or sister chromatids to separate during cell division.

Question 5. For the preparation of genetic maps, the recombination frequencies between genes are additive over short distances but not over long distances, due to

  1. Multiple crossover
  2. Lethal mutation
  3. Epistasis
  4. Synaptonemal complex

Answer:  1. Multiple crossover

  • The frequency of crossing over and hence recombination between two genes is directly proportional to the physical distance between the two.
  • In other words, two genes which are nearest to each other in the chromosomes will have least crossing over or recombination between them. On the other hand, two genes which have the maximum distance between them on the chromosome will have the maximum percentage of crossing over or recombination.
  • Thus, the recombination frequencies between genes are additive over short distances but not over long distances due to multiple crossover for the preparation of genetic maps.

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Question 6. Normally, all genes occur in pairs occupying position on the Xchromosome and not on Ychromosome. This indicates that

  1. Y-chromosome is larger than X-chromosome
  2. entire set of genes on X is different from those on Y-chromosome
  3. X-chromosome is larger than Y-chromosome
  4. X-chromosome is dominating with Y-chromosome

Answer:  3. X-chromosome is larger than Y-chromosome

Normally, all genes occur in pairs on the

  • X-chromosome and not on
  • Y-chromosome. This indicates that
  • X-chromosome is larger than
  • Y-chromosome. Y-chromosome is much shorter than the X-chromosome.

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Question 7. Crossing over in diploid organism is responsible for

  1. Segregation of alleles
  2. Recombination of linked alleles
  3. Dominance of genes
  4. Linkage between genes

Answer:  2. Recombination of linked alleles

Exchange of chromatid segments between the non-sister chromatids of a bivalent is called crossing over. It occurs during pachytene of prophase-I and it is responsible for recombination of genes.

Question 8. Alleles of different genes that are on the same chromosome may occasionally be separated by a phenomenon known as

  1. Pleiotropy
  2. Epistasis
  3. Continuous variation
  4. Crossing over

Answer:  4. Crossing over

Crossing over is separation of alleles of different genes that are present on the same chromosome.

Question 9. Genetic traits are often carried on separate chromosomes. Which of the following genotype represents a heterozygous dihybrid organism?

  1. TTRR
  2. TtRr
  3. Ttrr
  4. TtRr

Answer:  2. TtRr

Dihybrid organism is heterozygous for two particular factors. It is obtained by a cross between parents that are homozygous for two factors in consideration. A cross between TTRR and ttrr results into heterozygous dihybrid TtRr. Genetic traits are often carried on separate chromosomes.

Question 10. Recombination of alleles of two genes, A and B following crossing over will hypothetically result in four allelic recombinations. In the absence of crossing over, the two parental combinations would be formed as

  1. AB and ab type
  2. AB and Ab type
  3. ab and aB type
  4. AB, ab, Ab and aB

Answer:  1. AB and ab type

  • In normal conditions, there are chances of crossing over and four types of gametes are formed. These gametes show linkage in 50% of the gametes and 50% of the gametes are of recombination type.
  • The crossing over occurs in between the two non-sister chromatids of a homologous chromosome pair only and the other two chromatids are not involved. If there is no crossing over then, only two types of gametes will be formed. So, the parental combination would be AB and ab as 1:1 in the absence of recombination.

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Question 11. Linkage was discovered by

  1. Miller
  2. Morgan
  3. De Vries
  4. Mendel

Answer:  2. Morgan

  • The hypothesis that linked genes tend to remain in their original combinations because of their location in the same chromosome was given by TH Morgan in 1991.
  • Morgan stated that the pairs of genes of homozygous parent tend to enter in the same gametes and to remain together, whereas same genes from heterozygous parent tend to enter in the different gametes and remain apart from each other.

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Question 12. The unit of linkage map is

  1. Map unit
  2. Morgan
  3. CentiMorgan
  4. Both 1 and 3

Answer:  4. Both 1 and 3

In genetics, a centiMorgan (abbreviated cM) or map unit (mu) is a unit for measuring genetic linkage. It is defined as the distance between chromosome positions (also termed loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01.

Thus, option (4) is correct.

Question 13. Coupling and repulsion hypothesis was given by

  1. Bateson and Morgan
  2. Morgan and Punnett
  3. Bateson and Punnett
  4. Morgan and Muller

Answer:  3. Bateson and Punnett

Bateson and Punnett (1906) proposed that dominant alleles as well with recessive alleles tend to remain together due to gametic coupling. If dominant and recessive alleles are present in different parents, they tend to separate due to repulsion.

Question 14. The functional unit of gene is

  1. Cistron
  2. Muton
  3. Recon
  4. Exon

Answer:  1. Cistron

The functional unit of gene has been called cistron by Benzer because it is a chromosomal segment within which the cis-trans effect operates. The cistron represents a segment of the DNA molecule and consists of a linear sequence of nucleotides which controls some cellular functions.

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Question 15. Linkage was first suggested by

  1. Sutton and Boveri
  2. Morgan
  3. De Vries
  4. Pasteur

Answer:  1. Sutton and Boveri

Linkage was first suggested by Sutton and Boveri when they formulated the famous ‘chromosomal theory of inheritance’. Betason and Punnett (1906) while working on sweet pea also noticed that some factors remain together and do not show recombination or segregation.

Question 16. Linkage and crossing over are

  1. Same phenomena
  2. Different phenomena
  3. Opposite phenomena
  4. Identical phenomena

Answer:  3. Opposite phenomena

  • Strength of linkage between two genes is inversely proportional to the distance of two genes. This means, if two genes are closely placed then they have high percentage of linkage and if, they are placed far then there is low percentage of linkage.
  • Linkage and recombination are two opposite phenomena. In linkage, two genes remain united and in recombination, the two genes go apart due to crossing over during gametogenesis (meiosis).

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Question 17. Which of the following banding group is used in staining both plant and animal chromosomes?

  1. C-group
  2. G-group
  3. R-group
  4. N-group

Answer:  1. C-group

inheritance and variation mcq

  • Group banding is used in staining both plant and animal chromosomes. Chromosomes are stained with special fluorescent dyes that have differential affinity for difficult parts of chromosomes.
  • There are many types of staining techniques, which show different banding patterns. C-banding is common to both plants and animals. It stains region having constitutive heterochromatin.

Question 18. Frequency of crossing over will be relatively more if

  1. Distance between the two genes is less
  2. Distance between the two genes is more
  3. Linked genes are more
  4. Both 2 and 3

Answer:  2. Distance between the two genes is more

  • Frequency of actual crossing over is always proportional to the distance between the two genes. If two genes (mutations or markers) are far apart, the chance of crossing over between them and producing recombinant chromosomes is large.
  • If two genes are close together, the chance of crossing over between them is small.

Question 19. After crossing two plants, the progenies are found to be male sterile. This phenomenon is found to be maternally inherited and is due to some genes which reside in

  1. Mitochondria
  2. Cytoplasm
  3. Nucleus
  4. Chloroplast

Answer:  1. Mitochondria

  • In several crops like maize cytoplasmic control of male sterility is known. In such cases, if female parent is male sterile, F1 progeny would also be male sterile because cytoplasm is mainly derived from egg obtained from male sterile female parent.
  • Many experiments have proved that factors responsible for cytoplasmic male sterility are located in mitochondrial DNA. A particular phenotype arises because of dominant mutations in the mitochondrial genome.

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Question 20. Failure of the two homologous chromosomes to separate and move towards opposite poles during anaphase-I is called

  1. Crossing over
  2. Non-disjunction
  3. Linkage
  4. Recombination

Answer:  2. Non-disjunction

Non-disjunction is the condition in which the separation of chromosome does not take place
during cell division.

Question 21. Which of the following statements is not true about homologous recombination?

  1. Exchange of homologous segments
  2. Exchange takes place between two homologous DNA molecules
  3. It is also termed as general recombination
  4. It involves a direct exchange of sequences of DNA

Answer:  4. It involves a direct exchange of sequences of DNA

Statement in option (4) is not true and can be corrected as Homologous recombination involves
a reciprocal exchange of sequences of DNA. Rest other statements are true about homologous recombination.

Question 22. The cytoplasmic units of inheritance are called as

  1. Genome
  2. Lethal gene
  3. Plasmagenes
  4. All of these

Answer:  3. Plasmagenes

Cytoplasmic inheritance or non-chromosomal (extranuclear) inheritance is the passage of traits from parents to offspring through structures present inside the cytoplasm of contributing gametes. Plasmagenes occur in plastids, mitochondria, plasmids and some special particles like Kappa particles, sigma particles, etc. So, the cytoplasmic units of inheritance are called as plasmagenes.

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Question 23. A set of genes will be in a complete linkage when the progeny phenotypes for parental (P) and recombinant (R) types are

  1. P = 0%, R = 100%
  2. P = 50%, R = 50%
  3. P < 50%, R> 50%
  4. P = 100%, R = 0%

Answer:  4. P = 100%, R = 0%

  • In complete linkage, the progeny phenotypes are P = 100%, R = 0%. Here, P refers to parental type and R refers to recombinant type.
  • The genes located on the same chromosome do not separate and are inherited together over the generations due to the absence of crossing over.
  • It allows the combination of parental traits to be inherited and recombinant types are absent.

Question 24. The number of linkage group in E.coli is/are

  1. 4
  2. 2
  3. 1
  4. 5

Answer:  1. 1

  • Linkage group refers to the genes linked together in a single chromosome. Number of linkage groups in an organism is equal to its haploid number of chromosomes.
  • For example, in Drosophila, the haploid number (n) is 4 so linkage group is 4. But the number of linkage group in prokaryotes like E. coli is one. This is because bacteria being prokaryotes have a single circular chromosome only.

Question 25. Physical association of genes on a chromosome is called

  1. Repulsion
  2. Linkage
  3. Aneuploidy
  4. Duplication
  5. Polyploidy

Answer:  2. Linkage

Linked genes are present close together on a chromosome, making them likely to be inherited together. It refers to the physical association of genes on a chromosome. Thus, option (b) is correct.

inheritance and variation mcq

Question 26. In a test cross involving F1 dihybrid flies, more parental type offspring were produced than the recombinant type offspring. This indicates

  1. The two genes are linked and present on the same chromosome
  2. Both of the characters are controlled by more than one gene
  3. The two genes are located on two different chromosomes
  4. Chromosomes failed to separate during meiosis

Answer: 1. The two genes are linked and present on the same chromosome

If in a test cross involving F1 dihybrid flies more parental combinations appear as compared to the recombinants in F2 -generation, then it is indicative of involvement of linkage.

Linkage is the tendency of two different genes on the same chromosome to remain together during the separation of homologous chromosomes at meiosis.

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Question 27. What is pseudoallele?

  1. Allele with similar function
  2. Allele with similar structure
  3. Alleles with similar function and structure
  4. Alleles with similar function and different structure

Answer:  4. Alleles with similar function and different structure

When two types of allele have similar functions, but different structures, these are called pseudoalleles. These are located in close proximity.

Question 28. In sweet pea, genes C and P are necessary for colour in flowers. The flowers are white in the absence of either or both the genes. What will be the percentage of coloured flowers in the offspring of the cross Ccpp × ccPp?

  1. 75%
  2. 25%
  3. 100%
  4. 50%

Answer:  2. 25%

It is a dihybrid cross, Ccpp x ccPp (both are white). We know that in Ccpp x ccPp, Male gametes are Cp, cp Female gametes are cP, cp Hence, ratio = l (coloured): 3 (white), i.e. 25% coloured flowers.

NEET Biology Chromosomal Basis Of Inheritance Question 28

Question 29. Recombination of genes occur at

  1. Prophase-1 in mitosis
  2. Prophase-1 in meiosis
  3. Prophase-2 in meiosis
  4. Metaphase-2 in meiosis

Answer:  2. Prophase-1 in meiosis

Recombination occurs when two molecules of DNA exchange pieces of their genetic material with each other. It occurs during pachytene stage of prophase-1, of meiosis-1.

Question 30. Assertion (A) The linked genes tend to get inherited together. Reason (R) The link between them fails to break.

  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true, but R is not the correct explanation of A
  3. A is true, but R is false
  4. Both A and R are false

Answer:  1. Both A and R are true and R is the correct explanation of A

Both A and R are true and R is the correct explanation of A. When two genes are close together on the same chromosome, they do not assort independently and are said to be linked. The linked gene tends to get inherited together as the link between them fails to break.

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Question 31. Distance between two linked genes upon a chromosome is measured in crossover units. It is

  1. Ratio of crossing over between them
  2. Crossover value
  3. Number of other genes between them
  4. None of the above

Answer:  2. Crossover value

  • Distance between two linked genes upon a chromosome is measured in crossover units or the crossover value. Crossover unit is the percentage of recombinant in an organism.
  • In diploid organisms, most easily measured method is by crossing the double heterozygote to the double recessive. The percentage can never exceed 50%. This value gives the map distance between the two loci, used in chromosome mapping.

Question 32. Neurospora is widely used in genetic studies. Pick out the false statement.

  1. They can be cultured easily in the lab
  2. Being haploid the recessive gene can express themselves
  3. Crossing over is rare phenomenon and it cannot be detected
  4. They have short life cycle of 10 days

Answer:  3. Crossing over is rare phenomenon and it cannot be detected

Statementin option (3) is false and can be corrected as Neurospora follow Mendelian genetics which means that even closely placed genes are segregated independently and do not show linkage, but follow crossing to form new genetic combination. Rest statements are true.

Question 33. Neurospora is useful in genetics because Uttaranchal

  1. 8 ascospores are arranged linearly in ascus
  2. 4 ascospores are arranged linearly in ascus
  3. Of formation of ascospores
  4. Of formation of sac-like fruit body

Answer:  1. 8 ascospores are arranged linearly in ascus

  • Neurospora is an ascomycete fungus, haploid and grows as a mycelium. It has two mating types and fusion of nuclei of two opposite types leads to meiosis followed by mitosis.
  • The resulting 8 nuclei generate eight ascospores, arranged linearly in an ordered fashion in a pod-like ascus so that the various products of meiotic division can be identified.

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Question 34. Both chromosome and gene (Mendelian factors) whether dominant or recessive are transmitted from generation to generation in which form?

  1. Changed
  2. Unaltered form
  3. Altered form
  4. Disintegrated

Answer:  2. Unaltered form

Both genes and chromosomes (Mendelian factors) whether dominant or recessive are transmitted
from generation to generation in the pure or unaltered form. It is also called law of purity of gametes.

Question 35. A condition where a certain gene is present in only a single copy in a diploid cell is called

  1. Heterozygous
  2. Monogamous
  3. Homozygous
  4. Hemizygous

Answer:  4. Hemizygous

inheritance and variation mcq

  • A condition where only one gene or allele of allelic pair is present is called hemizygous condition. Other options are explained as Homozygous or pure organism have two similar genes or alleles for a particular character in a homologous pair of chromosomes, e.g. TT or tt.
  • Heterozygous or hybrid organism contains two different alleles or individuals contain both dominant and recessive genes of an allelic pair, e.g. Tt. Monogamy is the relationship of spending complete life with single partner

Question 36. If a gamete has 16 chromosomes, what will be the number of chromatids before anaphase-1?

  1. 8
  2. 16
  3. 32
  4. 64

Answer:  1. 8

After anaphase-I, the chromosome number doubles. As after anaphase-I, the number of chromosomes is 16. So, before anaphase-I, the number of chromosome would be n = 16/2 = 8 So, the cell has progressed from having 8 chromosomes to 16 chromosomes after anaphase-I.

Question 37. Chromosomes as well as genes occur in …A…. The two alleles of a gene pair are located on homologous sites on …B… chromosomes. Choose the correct choice for A and B.

  1. A-single, B-analogous
  2. A-pair, B-analogous
  3. A-pair, B-homologous
  4. A-single, B-heterozygous

Answer:  3. A-pair, B-homologous

Chromosome always occur in pair (A) and when located on homologous sites, they are called homologous (B) chromosome.

Question 38. Number of linkage groups in Pisum sativum

  1. 2
  2. 4
  3. 7
  4. 8

Answer:  3. 7

Number of linkage groups in Pisum sativum is 7 because it contain 14 chromosomes.

Question 39. The commonly used animal in genetics is

  1. Escherichia coli
  2. Drosophila
  3. Neurospora
  4. Chlorella

Answer:  2. Drosophila

  • A wide variety of animals have previously been used for animal testing including mice, flies and monkeys.
  • A particularly useful model organism is Drosophila melanogaster, a type of fruitfly. This fly has become the main invertebrate model used to study developmental genetics.

Question 40. Select the correct statement from the ones given below with respect to dihybrid cross.

  1. Tightly linked genes on the same chromosome show higher recombinations
  2. Genes far apart on the same chromosome show very few recombinations
  3. Genes loosely linked on the same chromosome show similar recombinations as the tightly linked
    ones
  4. Tightly linked genes on the same chromosome show very few recombinations

Answer:  4. Tightly linked genes on the same chromosome show very few recombinations

  • Statement in option (4) is correct with respect to dihybrid cross. When two genes are close together on the same chromosome, they do not assort independently and are said to be linked tightly.
  • They show less frequency of recombination. Whereas gene located on different chromosomes assort independently and have a recombination frequency of 50% .

Question 41. Name the sites of DNA, which have a high probability of crossing over?

  1. Cold spots
  2. Hot spots
  3. Covalent bond
  4. Hydrophobic bond

Answer:  2. Hot spots

There are certain sites on DNA, which have a high probability of crossing over. These are called hot spots. Those sites which have a low probability of crossing over are called cold spots.

Question 42. Determination of linkage and percentage of crossing over between two linked genes is important because

  1. It helps in the fixation of heterosis in the organism
  2. It helps in maintaining the heterozygosity in a given population
  3. It explains coupling and repulsion
  4. None of the above

Answer:  3. It explains coupling and repulsion

  • Coupling refers to the linkage of two dominant or two recessive alleles, whereas repulsion indicates that dominant alleles are linked with recessive alleles.
  • So, determination of linkage and percentage of crossing over between two linked genes is important because it explains coupling and repulsion.

Question 43. Which of the following is suitable for experiment on linkage?

  1. AaBB × aaBB
  2. AABB × aabb
  3. AaBb × AaBb
  4. AAbb × AaBB

Answer:  2.  AABB × aabb

AABB × aabb is suitable for experiment on linkage. Linkage is the tendency for certain genes to be inherited together, because they are on the same chromosome.

Thus, parental combinations of characters are found more frequently in offspring than non-parental characters..

Question 44. Which of the following statement is not true regarding linkage group?

  1. Group of physically linked genes
  2. Represent a haploid number of chromosomes
  3. Shown by linkage map
  4. Linkage groups are not correlated with each other

Answer:  4. Linkage groups are not correlated with each other

Statement in option (4) is not true and can be corrected as The number of linkage group can be
correlated as the number of homologous pairs. Rest statements are true regarding linkage group.

Question 45. The transference of genes from one chromosome to another during synapsis is termed as

  1. linkage
  2. dominance
  3. over
  4. Independent assortment

Answer:  3. C over

  • Crossing over is the reciprocal exchange of segments between non-sister chromatids of a pair of homologous chromosomes.
  • It results in recombination of genes. The non-sister chromatids in which exchange of segments take place, are known as crossovers or recombinants, while other chromatids not involved in exchange of segments are called non-crossovers or parental types.

Question 46.

Linked gene pair – Cross Value (COV)

T and U – 25

T and V – 5

V and U – 30

V and W – 10

In the table above, COV are mentioned for different linked gene pair. Find out the sequence of genes T, U, V, W on the chromosome.

VTWU

TVWU

BTWVU

VWTU

Answer:  1. VTWU

The genes which have higher COV (Cross Over Value) are placed farthest and genes which have lowest COV are placed close to each other. V and U have highest COV = 30, T and V have lowest COV = 5. After gathering the other COV, the sequence of genes will be VTWU. It can be understood by the linkage map given below.

NEET Biology Chromosomal Basis Of Inheritance Question 46

Question 47. The distance between the genes a, b, c, and d in mapping units are a-d = 3.5, b-c = 1, a-b = 6, c-d = 1.5, a-c = 5 Find out the sequence of arrangement of these genes.

  1. Acdb
  2. Abcd
  3. Acbd
  4. Abdc
  5. Adcb

Answer:  5. Adcb

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Chromosome mapping is based on the fact that genes are linearly arranged in the chromosome and frequency of crossing over is directly proportional to the distance between two genes. So, the sequence of arrangement of given genes is adcb as shown below

NEET Biology Chromosomal Basis Of Inheritance Question 47

Question 48. Two genes R and Y are located very close on the chromosomal linkage map of maize plant. When RRYY and rryy genotypes are hybridised, the F2 segregation will show

  1. Segregation in the expected 9 : 3 : 3: 1 ratio
  2. Segregation in 3:1 ratio
  3. Higher number of the parental types
  4. Higher number of the recombinant types

Answer:  3. Higher number of the parental types

  • The closely located gene show the tendency of linkage and they are transmitted together to the next generation.
  • If two closely located genes show linkage, they do not show crossing over and result in formation of higher number of the parental type.

Question 49. The total number of progeny obtained through dihybrid cross of Mendel is 1280 in F2-generation. How many of them are recombinants?

  1. 240
  2. 360
  3. 480
  4. 720

Answer:  3. 480

The total number of progeny obtained through dihybrid cross of Mendel is 1280 in F2-generation. Out of these, 480 will be recombinant. In a dihybrid cross, the ratio of pure to recombinant is 10: 6. So, when total progeny is 1280, 800 would be pure and rest are recombinant.

Pure =  \(\frac{10}{16}\)× 1280

=  800

Recombinant =  \(\frac{6}{16}\)× 1280

= 480

Question 50. How many linkage groups are present in man?

  1. 23 linkage groups
  2. 46 linkage groups
  3. 22 linkage groups
  4. 44 linkage groups

Answer:  1. 23 linkage groups

Number of linkage groups in a species corresponds to its haploid number of chromosomes. Therefore, 23 linkage groups are present in man.

Question 51. Two linked genes, a and b show 20% recombination. The individuals of a dihybrid cross between ++/ ++ ab/ab shall show gametes

  1. + + 80 : ab: 20
  2. + + 50 : ab: 50
  3. + + 40 : ab 40: + a 10 : + b: 10
  4. + + 30 : ab 30: + a 20: + b: 20

Answer:  3. + + 40 : ab 40: + a 10 : + b: 10

The combined linkage frequency between parental combination ++ and ab is 80%. The combined recombination frequency between recombinant combination + a and + b is 20%. The individual frequencies would be half of combined frequency, i.e. ++ 40: ab 40: + a 10: +b: 10.

Question 52. Which of the following statements is not true for two genes that show 50% recombination frequency?

  1. The genes are tightly linked
  2. The genes show independent assortment
  3. If genes present on same chromosome, they undergo many crossover in every meiotic division
  4. The genes may be on different chromosomes

Answer:  1. The genes are tightly linked

  • Statement in option (1) is not true for two genes that show 50% recombination frequency and can be corrected as Tightly linked genes show more linkage than crossing over.
  • The genes that show 50% recombination frequency would undergo crossing over. Rest statements are true.

Question 53. Which of the following is site specific recombination?

  1. Modification
  2. Transposition
  3. Holiday junction
  4. Retrotransposons

Answer:  2. Transposition

Transposition is the process of recombination, which allows one DNA sequence to inserted in another without taking care of sequence homology.

Question 54. Bateson and Punnett (1909) discovered linkage while working on

  1. Pisum sativum
  2. Lathyrus odoratus
  3. Drosophila melanogaster
  4. Lychmis alba

Answer:  2. Lathyrus odoratus

Linkage was 1st discovered by Bateson and Punnett while experimenting on sweet pea, Lathyrus odoratus.

Question 55. Which of the following is not a recombination system?

  1. RecBCD
  2. RecE
  3. RecF
  4. DnaF

Answer:  4. DnaF

Homologous recombination was first described in bacterial systems. The three different recombination systems are RecF, RecE, and RecBCD. So, DNA F is not a recombination system.

Question 56. Percentage of recombination between A and B is 9%, A and C is 17%, B and C is 26%. Then the arrangement of genes is

  1. ABC
  2. ACB
  3. BCA
  4. BAC

Answer:  4. BAC

By manipulating the three possibilities of gene arrangements A-B-C, A-C-B and B-A-C, it was found that the three genes must be arranged in the order B-A-C with the distance between B-A being 9 cm and A-C being 17 cm and the distance between B-C being 26 cm. Order of genes is shown below

NEET Biology Chromosomal Basis Of Inheritance Question 56

Thus, option (4) is correct.

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Question 57. Assertion (A) The percentage frequency with which a gene successfully manifests its phenotypic effect is called expressivity. Reason (R) The extent or intensity of phenotypic expressions of certain genes may vary in different individuals due to environmental influences.

  1. Both A and R are true and R is the correct explanation of A
  2. Both A and R are true, but R is not the correct explanation of A
  3. A is true, but R is false
  4. Both A and R are false

Answer:  2. Both A and R are true, but R is not the correct explanation of A

  • Both A and R are true, but R is not the correct explanation of A. Expressivity is a measure for describing the range of phenotypic expression.
  • It measures the extend to which a given phenotype is expressed at the phenotypic level. Different degrees of expression in different individual may be due to variation in the allelic constitution of the rest of the genome or due to environmental factors.

Question 58. If you cross a white eyed female, Drosophila with a red eyed male, Drosophila what will be the colour of eyes for their male and female offspring?

  1. Both red eyed
  2. Both white eyed
  3. Red eyed daughter and white eyed son
  4. Red eyed son and white eyed daughter

Answer:  3. Red eyed daughter and white eyed son

  • Eye colour is a sex-linked trait. In this case, the F1 male progeny was red eyed, as the father only gave the Y-chromosome and not X which determines eye colour.
  • Then similarly, the F2 sons would be white eyed by allele from their mother, female will be red eyed as they get both alleles.

Question 59. Fruitfly is excellent model for genetics because of

  1. Small life cycle (two weeks).
  2. Can be bred on simple synthetic medium.
  3. Single mating produces large number of progeny.
  4. Clear differentiation of sexes.
  5. Many heredity variations can be seen with low power microscopes.

Choose the correct option.

  1. 1, 2 and 3
  2. 3, 4 and 5
  3. 1, 4 and 5
  4. 1, 2, 3, 4 and 5

Answer:  4. 1, 2, 3, 4 and 5

All given statements are correct in describing fruitfly as an excellent model for the genetics. Thus, option (4) is correct.

Biology MCQ For NEET With Answers

Question 60. Walter Sutton is famous for his contribution to

  1. Genetic engineering
  2. Totipotency
  3. Quantitative genetics
  4. Chromosomal theory of inheritance

Answer:  4. Chromosomal theory of inheritance

Chromosomal theory of inheritance was given by Walter Sutton. He worked with grasshopper chromosomes and showed that chromosomes occur in distinct pairs which segregate during meiosis.

Question 61. Out of 8 ascospores formed in Neurospora the arrangement is 2a: 4a: 2a showing

  1. No crossing over
  2. Some meiosis
  3. Second generation division
  4. First generation division

Answer:  3. Second generation division

In Neurospora, after crossing over between the gene and centromere, the paired arrangement of ascospores is AAaaaaAA or 2a: 4a: 2a. This is called second division segregation.

Question 62. Depending upon the distance between any two genes which is inversely proportional to the strength of linkage, crossovers will vary from

  1. 50-100%
  2. 0-50%
  3. 75-100%
  4. 100-150%

Answer:  2. 0-50%

  • Depending upon the distance between any two genes which is inversely proportional to strength of linkage, non-crossover will vary from 50-100%.
  • 100% non- crossover is a state where no crossing over takes place as in male Drosophila. The crossover will similarly vary from 0-50% and will never exceed 50 %.

Question 63. Which of the following shows linkage group in coupling phase?

NEET Biology Chromosomal Basis Of Inheritance Coupling Phase

Answer:  Diagram in option (1) shows linkage group in coupling phase. The two alleles A and B are located on same gene and are inherit together. In other three diagrams, the alleles A and B are located on different genes.

Biology MCQ For NEET With Answers

Question 64. Fusion of homologous chromosomes from the same parent is known as

  1. Auxesis
  2. Autosyndesis
  3. Wading
  4. None of the above

Answer:  2. Autosyndesis

Autosyndesis is the fusion of pair of homologous chromosomes from the same parent during meiosis in polyploids.

Question 65. Which of the following is true about linkage?

  1. It is phenomenon in which more recombinants are produced in F2 -generation.
  2. More parental combinations are produced in F1 -generation.
  3. Genotypes which are present in F1 hybrid reappear in high frequency in F2-generation.
  4. It is a phenomenon in which two chromosomes are linked.

Choose the correct option.

  1. Only 1
  2. Only 2
  3. 1 and 3
  4. 3 and 4

Answer:  2. Only 2

Only statement II is correct, while other three are incorrect. In linkage, two alleles of a gene are linked. So that the number of recombinants produced in F2-generation are very less or negligible.

inheritance and variation mcq

Question 66. The frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes was explained by

  1. TH Morgan
  2. Gregor J Mendel
  3. Alfred Sturtevant
  4. Sutton Boveri

Answer:  3. Alfred Sturtevant

Alfred Sturtevant explained chromosomal mapping on the basis of recombination frequency which is directly proportional to distance between two genes on same chromosome.

Question 67. Incomplete linkage is …A… whereas complete linkage is …B… . Choose correct option for A and B.

  1. A-common, B-rare
  2. A-rare, B-common
  3. A-impractical, B-practical
  4. A-practical, B-impractical

Answer:  1.  A-common, B-rare

Question 68. Study the given test cross and choose the correct option for F2-generation.

NEET Biology Chromosomal Basis Of Inheritance F2 Generation

  1. Hybrid cross (9:3:3:1)
  2. Hybrid cross (3:1)
  3. Dihybrid cross (12:4)
  4. Dihybrid linked gene cross (3:1)

Answer:  4. Dihybrid linked gene cross (3:1)

Option (4) is correct for F2 -generation. The linked genes do not show independent assortment but remain together and are inherited enblock producing only parental type of progeny. They give a dihybrid ratio of 3: 1 and a test cross ratio of 1: 1.

Question 69. Cytological basis of crossing over was first established by

  1. TH Morgan Chandigarh
  2. Correns
  3. Castle and Mendel
  4. CB Bridges

Answer:  1. TH Morgan Chandigarh

Cytological basis of crossing over was described in theory by Thomas Hunt Morgan. The physical basis of crossing over was first demonstrated by Harriet Creighton and Barbara McClintock in 1931.

Biology MCQ For NEET With Answers

Question 70. When the number of recombinant progeny is usually less than the number expected in independent assortment it is called

  1. Complete linkage
  2. Incomplete linkage
  3. Complete recombination
  4. Complete independent assortment

Answer:  2. Incomplete linkage

In incomplete linkage, some recombinant progenies are produced, but their percentage is very less as expected in independent assortment.

Question 71. Mendel conducted a number of crosses and studies but could never discover linkage. What could be the reason for this?

  1. Some genes are linked but they are too far apart for crossing over to be distinguished from
    independent assortment.
  2. Linked genes were never tested for the same time in same cross.
  3. The seven genes were present on the 7 chromosomes.
  4. The genes underwent mutations during subsequent crossings.

Choose the correct option.

  1. 1 and 2
  2. 2 and 3
  3. and 4
  4. Only 4

Answer:  1. 1 and 2

  • Statement 1 and 2 are correct while 3 and 4 are incorrect. Mendel could not find out linkage because all of his experimental characters of pea were not linked.
  • They were present far apart from each other on four different chromosomes. Thus, option (a) is correct.

Question 72. Mendel did not observe linkage due to

  1. Mutation
  2. Synapsis
  3. Crossing over
  4. Independent assortment

Answer:  4. Independent assortment

Principle of law of independent assortment is applicable to only those factors or genes which are present on different chromosomes. Mendel did not observe linkage due to independent assortment of alleles.

Question 73. The linkage map of X chromosomes of fruitfly has 66 units, with yellow body gene (y) at one end and bobbed hair (b) gene at other end. The recombination progeny between these two genes (y and b) should be

  1. <50%
  2. 100%
  3. 66%
  4. >50%

Answer: 1. <50%

  • X -chromosome has 66 crossover units with yellow and bobbed genes at two extreme ends of the map.
  • Recombination frequency never exceeds 50% (< 50%) between any two loci, but these 66 units will actually be obtained by making use of a mapping function.

Question 74. If the genes are located in a chromosome as A—B—C—D—E— O—-T. Which of the gene pairs will have least probability of being inherited together?

  1. C and D
  2. A and T
  3. A and B
  4. O and T

Answer:  2. A and T

Longer is the distance, lesser will be the probability of the two genes being inherited together as there will be a greater chance of recombination. Thus, A and T would not inherit together.

Question 75. Bateson used the term coupling and repulsion for linkage and crossing over. Choose the correct coupling and repulsion combination. Coupling Repulsion

  1. AABB, aabb AAbb, aaBB
  2. AABB, aabb AABB, AAbb
  3. AAbb, aaBB AaBb, aabb
  4. aaBB, aabb AABB, aabb

Answer: 1. AABB, aabb AAbb, aaBB

  • Bateson gave the coupling and repulsion hypothesis for linkage and crossing over. Similar genes remain together and do not undergo crossing over.
  • Bateson called them coupling genes. While on the other hand, dissimilar genes segregate and crossing over takes place. Bateson called them repulsion parent’s gene. The correct coupling and repulsing combination is AABB, aabb and AAbb aaBB, respectively.

Question 76. Number of linkage groups in Drosophila are

  1. 4
  2. 8
  3. 6
  4. 10

Answer:  1. 4

The number of linkage groups present in an individual corresponds to the number of chromosomes in its haploid genome. Fruitfly, Drosophila melanogaster has four linkage groups (4 pairs of chromosomes).

Question 77. The jumping gene in maize was discovered by

  1. HG Khorana
  2. Barbara McClintock
  3. Beadle and Tatum
  4. TH Morgan

Answer:  2. Barbara McClintock

Transposons or jumping genes was discovered by Barbara McClintock (1951) in maize.

Question 78. A diagram of the chromosomes of a fruitfly is given below. Labels A, B, C and D are marked to various chromosomes. Choose the correct option that indicates an autosome labelled.

NEET Biology Chromosomal Basis Of Inheritance Autosome Labelled

  1. C
  2. A
  3. B
  4. D

Answer:  3. B

Drosophila have 3 pairs of autosome and one pair sex chromosome. Sex-determination in Drosophila is exactly similar to the human beings, i.e. female is homogametic and male is heterogametic.

In the given diagrams, first diagram belongs to the female Drosophila and second diagram belongs to the male Drosophila.

  • Indicates X-chromosomes in female, Drosophila.
  • Indicates Autosome
  • Indicates X-chromosome in male, Drosophila.
  • Indicates Y-chromosome in male, Drosophila.

Thus, option (3) is correct.

Question 79. Maize has ten pairs of chromosomes. How many linkage groups will be present, if all the genes are mapped?

  1. 20
  2. 5
  3. 40
  4. 10

Answer:  4. 10

The number of linkage groups present in an individual corresponds to number of chromosomes in its haploid genome (all the chromosomes, if haploid or homologous pairs, if diploid). Maize has 10 linkage groups, as it has 10 pairs of chromosomes (haploid set is 10).

Question 80. A and B genes are linked. What shall be genotype of progeny in a cross between AB/ab and ab/ab?

  1. AAbb and aabb
  2. AaBb and aabb
  3. AABB and aabb
  4. None of the above

Answer:  2. AaBb and aabb

  • The tendency of potential combinations to remain together, which is expressed in terms of low frequency of recombinations (new combinations) is called linkage.
  • Genes present on same chromosomes show linkage. These genes are called linked genes. Since, A and B genes are linked they will be passed on together in the progeny. Thus, the genotype of progeny would be AaBb and aabb.

Question 81. Which one of the following information is essential to determine the genetic map distance between two genes located on the same chromosome?

  1. Length of the particular chromosome
  2. Number of genes present in the particular chromosome
  3. Number of nucleotides in the particular chromosome
  4. Percentage of crossing over or recombinant frequency between the two genes

Answer:  4. Percentage of crossing over or recombinant frequency between the two genes

A genetic map is a linear, graphic representation of the sequence and relative distances of various genes present in a chromosome. The distance between two genes located on the same chromosome is directly proportional to percentage of crossing over or recombination frequency between the two genes.

Question 82. Two dominant non-allelic genes are 50 map units apart. The linkage is

  1. Cis type
  2. Trans type
  3. Complete
  4. Absent/ incomplete

Answer:  4. Absent/ incomplete

When two dominant non-allelic genes are 50 map units apart, the linkage is absent or incomplete. At or above this distance, crossing over and formation of recombinants is favoured.

Question 83. In sex linkage, the speciality is

  1. Atavism
  2. Criss-cross inheritance
  3. Reversion
  4. Gene flow

Answer:  2. Criss-cross inheritance

  • Sex linkage or sex-linked gene (X-linked gene) has a characteristic inheritance pattern which is called ‘criss -cross inheritance’. In this case, the X-linked gene is transmitted from father to grandsons through its carrier daughters.
  • It was first studied by Morgan (1910) in case of eye colour in Drosophila. This type of inheritance is applicable to most sex-linked disorders in humans, e.g. colour blindness, haemophilia, etc.

Question 84. If 5% is the strength of linkage between two genes, then they are 5 map units apart on same chromosome. This statement is

  1. False
  2. Controversial
  3. True
  4. Either 1 or 3

Answer:  2. Controversial

Given statement is controversial. One Linkage Map Unit (LMU) is 1% recombination. Thus, the linkage map distance between two genes is the percentage of recombination (crossover) between these genes. Thus, percentage of strength of linkage does not express as map unit.

Question 85. Crossing over that results in genetic recombination in higher organisms occurs between

  1. Two different bivalents
  2. Sister chromatids of bivalent
  3. Non-sister chromatids of bivalent
  4. Two different nuclei

Answer:  3. Non-sister chromatids of bivalent

Crossing over takes place between non-sister chromatids of bivalent.In sisters chromatids, the crossing over does not take place.

Question 86. What map unit (centiMorgan) is adopted in the construction of genetic maps?

  1. A unit of distance between two expressed genes representing 10% cross over
  2. A unit of distance between two expressed genes representing 100% crossover
  3. A unit of distance between genes on chromosomes, representing 1% crossover
  4. A unit of distance between genes on chromosomes, representing 50% crossover

Answer:  3. A unit of distance between genes on chromosomes, representing 1% crossover

1 map unit represents 1% crossover. Map unit is used to measure genetic distance. This genetic distance is based on average number of cross over frequency. Thus, option (c) is correct.

Question 87. There are three genes a, b, c. Percentage of crossing over between a and b is 20%, b and c is 28% and a and c is 8%. What is the sequence of genes on chromosome?

  1. b, a, c
  2. a, b, c
  3. a, c, b
  4. None of these

Answer:  1. b, a, c

inheritance and variation mcq

Percentage of crossing over between a and b is 20%, so they are 20 map distance apart, b and c are 28 map distance apart and a and c are 8 map distance apart.

NEET Biology Chromosomal Basis Of Inheritance Percentage Of Crossing

So, that the correct sequence of genes on chromosomes will be b, a, c.

Question 88. In sex linkage, reciprocal cross yields

  1. Cross results
  2. Identical results
  3. Distinct results
  4. None of the above

Answer: 1. Cross results

In the case of sex linkage, reciprocal cross does not yield identical results, but it shows a criss-cross inheritance pattern, i.e. male transmits its sex-linked genes to all daughters, who in turn transmit them to half of their male progeny.

 

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