Question

Which of the following symbols are used for representing sex chromsosmes of birds?
A. ZZ- ZW
B. XX - XY
C. XO - XX
D. ZZ - WW

Answer 1

Hint: Chromosomes are threadlike structures which are present in the nucleus and they carry genetic information from one generation to another generation. In eukaryotes, they are present in the nucleus of the cell. There are two types of chromosomes - sex chromsomes and autsomes.

Complete answer:
The word chromosomes mean ‘coloured body.’ In humans, there are 23 pairs of chromosomes, out of which 22 pairs are autosomes and 1 pair is sex chromosomes.

Option A: Birds have sex chromsomes - ZZ- ZW type. In this system, males have two similar chromosomes ZZ and the females have dissimilar ZW chromosomes. Thus, the females are heterozygotic and the males are monozygotic. It is also to be noted that the Z chromosome is larger and has a higher number of genes.

Option B: XX - XY type sex chromsomes are seen in humans and not birds. In this type, the females are monozygotic (XX) and males are heterozygotic (XY) and the X chromosome is larger than Y and has more genes.

Option C: XO - XX type chromosomes are seen in insects like grasshopper, etc. The female is homozygous (XX) and the male is hetergametic sex as it has only one sex chromsome (XO). The male has the ability to produce gametes X or without O sex chromosome.

Option D: ZZ - WW is an incorrect sex chromsome type, as the correct type is ZZ - ZW. ZZ is found in males and ZW is found in females.

Thus, the correct option is A) ZZ - ZW.

Note: The function of chromosomes are,
- They have an important role in the process of growth,reproduction, regeneration and repair process.
- Their major function is to carry genetic materials from one generation to another.
- Every chromosome is made up of thousands of genes which code for multiple proteins in the body.
- The sex chrosmomes helps in sex determination.