Principles of Inheritance and Variation — Page 2 | NEET Biology

Q11

In a certain plant, red fruit (R) is dominant over yellow (r) and tallness (T) over shortness (t). A plant with RRTt is crossed with rrtt. The percentage of tall plants with red fruits in progeny is

A 50%

B 100%

C 75%

D 25%

Correct Answer

Option A

Solution

(a) RRTt x rrtt: all red (Rr); Tt x tt gives 50% tall. So 50% are tall red.

Q12

What map unit (Centimorgan) is adopted in the construction of genetic maps?

A A unit representing 10% crossover

B A unit representing 100% crossover

C A unit representing 1% crossover

D A unit representing 50% crossover

Correct Answer

Option C

Solution

(c) 1 centimorgan (cM) = 1% recombination frequency.

Q13

A self-fertilizing trihybrid plant forms how many different gametes?

A 8 different gametes and 64 different zygotes

B 4 different gametes and 4 different zygotes

C 8 different gametes and 8 different zygotes

D 16 different gametes and 64 different zygotes

Correct Answer

Option A

Solution

(a) Trihybrid (AaBbCc) forms 2^3 = 8 gamete types and 4^3 = 64 zygote types.

Q14

A male human is heterozygous for autosomal genes A and B and hemizygous for hemophilic gene h. What proportion of his sperms will be abh?

A 1/8

B 1/32

C 1/16

D 1/4

Correct Answer

Option A

Solution

(a) P(a) = 1/2, P(b) = 1/2, P(h) = 1/2; P(abh) = 1/8.

Q15

The recessive genes located on X-chromosome in humans are always

A lethal

B sub-lethal

C expressed in males

D expressed in females

Correct Answer

Option C

Solution

(c) Males are hemizygous for X-linked genes, so all X-linked alleles are expressed.

Q16

Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to

A repulsion

B recombination

C linkage

D crossing over

Correct Answer

Option C

Solution

(c) Linkage (genes on same chromosome) prevents independent assortment.

Q17

A woman with normal vision but whose father was colour blind marries a colour blind man. Their fourth child is a boy. This boy

A may be colour blind or may be of normal vision

B must be colour blind

C must have normal colour vision

D will be partially colour blind

Correct Answer

Option A

Solution

(a) Woman is carrier (X^C X); man is colour blind (X^c Y). Sons can be normal or colour blind (50:50).

Q18

The salivary gland chromosomes in dipteran larvae are useful in gene mapping because

A these are fused

B these are much longer in size

C these are easy to stain

D They have endoreduplicated chromosomes

Correct Answer

Option D

Solution

(d) Polytene chromosomes are giant chromosomes formed by endoreduplication.

Q19

At a particular locus, frequency of A allele is 0.6 and a is 0.4. The frequency of heterozygotes in a random mating population at equilibrium is

A 0.36

B 0.16

C 0.24

D 0.48

Correct Answer

Option D

Solution

(d) Frequency of heterozygotes = 2pq = 2 x 0.6 x 0.4 = 0.48.

Q20

In order to find out the different types of gametes produced by a pea plant with genotype AaBb, it should be crossed to

A AABB

B AaBb

C aabb

D aaBB

Correct Answer

Option C

Solution

(c) Test cross with aabb reveals all gamete types of AaBb.