Principles of Inheritance and Variation — Page 14 | NEET Biology

Q131

Mental retardation in man associated with sex chromosomal abnormality is usually due to

A increase in X complement

B moderate increase in Y complement

C large increase in Y complement

D reduction in X complement

Correct Answer

Option A

Solution

(a) Extra X chromosomes (e.g., XXY, XXX, XXXX) are associated with mental retardation.

Q132

Red-green colour blindness: a normal woman whose father was colour blind marries a colour blind man. Proportion of daughters expected to be colour blind is

A 3/4

B 1/2

C 1/4

D All

Correct Answer

Option B

Solution

(b) Woman is X^c X (carrier); man is X^c Y. Daughters: 1/2 X^c X^c (colour blind) and 1/2 X^c X (carrier).

Q133

One child is haemophilic while its fraternal twin brother is normal. The most appropriate information is

A The mother must have been heterozygous

B The child is a monozygotic twin

C The other child is a female and father is haemophilic

D The haemophilic child is a male

Correct Answer

Option A

Solution

(a) Mother is X^H X^h (carrier); one son received X^h (haemophilic) and the other received X^H (normal).

Q134

Sickle cell anaemia is induced by change of amino acid in

A a-chain of haemoglobin

B b-chain of haemoglobin

C both a- and b-chain

D either a- or b-chain

Correct Answer

Option B

Solution

(b) Glutamic acid is replaced by valine in the 6th position of the beta-globin chain.

Q135

In humans, male XXY and female XXXX occur due to

A aneuploidy

B euploidy

C autosomal syndrome

D none of these

Correct Answer

Option A

Solution

(a) Aneuploidy = abnormal number of individual chromosomes (gain or loss of one or a few).

Q136

Which of the following is an example of pleiotropic effect?

A Haemophilia

B Thalassemia

C Sickle cell anaemia

D Colour blindness

Correct Answer

Option C

Solution

(c) Sickle cell anaemia gene shows pleiotropy: affects RBC shape, oxygen transport, and provides malaria resistance.

Q137

Which of the following is an example of sex linked disease?

A AIDS

B Colour blindness

C Syphilis

D Gonorrhoea

Correct Answer

Option B

Solution

(b) Colour blindness is an X-linked recessive disorder.

Q138

Correct match: Down syndrome - chromosome 21

A Down syndrome - 21st chromosome

B Sickle cell anaemia - X-chromosome

C Haemophilia - Y-chromosome

D Parkinson disease - X & Y chromosome

Correct Answer

Option A

Solution

(a) Down syndrome is caused by trisomy of chromosome 21.

Q139

Down syndrome is caused by extra copy of chromosome 21. Percentage of offspring from an affected mother and normal father that would be affected is

A 25%

B 100%

C 75%

D 50%

Correct Answer

Option D

Solution

(d) Affected mother produces 50% normal (n) and 50% trisomic (n+1) ova; 50% of offspring affected.

Q140

Christmas disease is another name for

A sleeping sickness

B haemophilia B

C hepatitis B

D Down syndrome

Correct Answer

Option B

Solution

(b) Christmas disease = haemophilia B (factor IX deficiency), named after Stephen Christmas.