Question

Explain mechanism of sex-determination in birds.

Answer 1

Hint: Chromosomes are of two types: Autosomes and allosome. Sex chromosomes or allosomes in birds are ‘Z’ and ‘W’. For male it is ‘ZZ’ chromosomes and for females it is ‘ZW’ chromosomes.

Complete answer:
In sexual reproduction, there are two different sexes which are involved. There are various factors which help in sex determination. in certain animals, its the temperature which has a role in sex determination. In humans, the sex of a child can be determined genetically.
In bird’s sex-determination is: little different than human, ‘ZZ’ male is homomorphic. Chomo s-same, morphe-form ‘ZW’ female is heteromorphic.
‘Z’ chromosome is a large chromosome and contains almost all the known sex linked genes.
‘W’ chromosome is a smaller one which contains a high proportion of repeat patterns of DNA.
‘W’ chromosomes have female determining properties.

In human beings male heterogametic and has XY sex chromosomes and the human female is homogametic with XX sex chromosomes. As males are heterogametic, they are the one responsible for the sex of the foetus and not females.
Additional information: Various particles have been developed to differentiate the sex of birds on the basis of sex-linked genes, the amount of DNA per cell and using DNA probes for sex linked sequences.

Note: The different kinds of sex determination in different animals are,
i) XO - XX type chromosomes are seen in insects like grasshopper, etc.
ii) XX - XY type sex chromsomes are seen in humans.
iii) Birds have sex chromsomes - ZZ- ZW type.