Describe the chromosomal basic of sex determination in human,honey bee and birds.

Explanation

Chromosomal basis of sex-determination in human, honeybee and birds is as follows
(i) Sex-Determination in Humans
In males (XY), 50% of sperms carry
X-chromosomes and the remaining 50% carry
Y-chromosomes. In females (XX), all ova carry
X-chromosomes. The sex of an individual is determined by the type of sperms which fertilised by
Y-chromosome, the zygote (XY) develops into a male and if the ovum is fertilised by
X-chromosome, zygote (XX) develops into a female.

(ii) In Honeybee
Haploid-diploid method In this method, the unfertilised egg develops into male
(Arrhenotoky) while fertilised egg develops into female. This type of sex-determination is the characteristic feature of insects like honeybees, ants, etc.
(iii) In Birds
It is the ZZ-ZW type of sex-determination method commonly seen in birds, fowls and fishes. In this type, females carry one Z and one W-chromosome along with autosomes, whereas males have a pair of Z-chromosome.

Thus, the sex of an organism is determined by the type of ovum that is fertilised to produce offspring. In this type of sex-determination, total number of chromosomes is same in both males and females. But females produce two different types of gametes adn are thus known as heterogametes.