Principles of Inheritance and Variation — Page 11 | NEET Biology

Q101

Which one of the following is a wrong statement regarding mutations?

A Deletion and insertion of base pairs cause frame-shift mutations

B Cancer cells commonly show chromosomal aberrations

C UV and Gamma rays are mutagens

D Change in a single base pair of DNA does not cause mutation

Correct Answer

Option D

Solution

(d) Point mutation = change in a single base pair; it does cause mutation (e.g., sickle cell anaemia).

Q102

Down syndrome in humans is due to

A Two Y chromosomes

B Three X chromosomes

C Three copies of chromosome 21

D Monosomy

Correct Answer

Option C

Solution

(c) Down syndrome = trisomy 21 (47 chromosomes).

Q103

The incorrect statement with regard to Haemophilia is

A It is a recessive disease

B It is a dominant disease

C A single protein involved in blood clotting is affected

D It is a sex-linked disease

Correct Answer

Option B

Solution

(b) Haemophilia is X-linked recessive, not dominant.

Q104

If both parents are carriers for thalassemia (autosomal recessive), chances of an affected child are

A 50%

B 25%

C 100%

D no chance

Correct Answer

Option B

Solution

(b) Carrier × Carrier (Aa × Aa): 25% affected (aa).

Q105

A man whose father was colour blind marries a woman who had a colour blind mother and normal father. Percentage of male children who will be colour blind is

A 25%

B 0%

C 50%

D 75%

Correct Answer

Option C

Solution

(c) Man is colour blind (X^c Y); woman is carrier (X^c X). Sons: 50% colour blind.

Q106

A pleiotropic gene controls

A a gene evolved during Pliocene

B a trait only in combination with another gene

C multiple traits in an individual

D is expressed only in primitive plants

Correct Answer

Option C

Solution

(c) A pleiotropic gene has multiple phenotypic effects, e.g., sickle cell gene affects RBC shape, oxygen carrying, malaria resistance.

Q107

An abnormal human baby with XXX sex chromosomes was born due to

A formation of abnormal ova in the mother

B fusion of two ova and one sperm

C fusion of two sperms and one ovum

D formation of abnormal sperms in the father

Correct Answer

Option A

Solution

(a) XXX results from non-disjunction of X chromosomes in the mother producing an XX ovum.

Q108

A colour blind man marries a woman with normal sight who has no history of colour blindness. The probability of their grandson being colour blind is

A 1

B Nil

C 0.25

D 0.5

Correct Answer

Option C

Solution

(c) Daughters are all carriers; if a carrier daughter marries normal man, 25% of their sons will be colour blind.

Q109

Which of the following most appropriately describes haemophilia?

A Recessive gene disorder

B X-linked recessive gene disorder

C Chromosomal disorder

D Dominant gene disorder

Correct Answer

Option B

Solution

(b) Haemophilia A and B are X-linked recessive disorders affecting blood clotting.

Q110

A disease caused by autosomal primary non-disjunction is

A Klinefelter syndrome

B Turner syndrome

C Sickle Cell Anemia

D Down Syndrome

Correct Answer

Option D

Solution

(d) Down syndrome is caused by trisomy of chromosome 21 due to non-disjunction.