Question

Which of the following statements are correct?

1. X chromosome has large amount of euchromatin.
2. heterochromatin is genetically inert. 
3. Both X and Y chromosomes are homologous.
4. Crossing over does not take place in sex chromosomes in female.

Choose the correct option.

Options

• i and ii only

• ii and iii only

• i, ii and iii only

• iii and iv only

Answer 1

i and ii only

Explanation:

The X chromosome is rich in transcriptionally active euchromatin (i), while heterochromatin is densely packed and genetically inactive (ii). Statement (iii) is incorrect because X and Y are largely non-homologous, and (iv) is false as crossing over does occur between the two X chromosomes in females.