(a) In humans, males are heterogametic and females are homogametic, Explain. Are there any examples where males are homogametric and females are heterogametic ? (b) Also describe as to, who determines the sex of an unborn child ? Mension whether temperature has a role in sex determination.

Explanation

(a) (i) The term homogametic and heterogamete refer to the organism depending upon whether all the gametes contain one type of sex chromosome (Homo = same) or two different types of sex chromosomes (Hetero = different) Humans show XXXY type of determination i.e. Females contain 2 copies of X chromosome and males contain 1 X & 1 Y chromosome. Therefore, ova produced by females contain the same sex chromosome i.e. X. On the other hand the sperms contain 2 different types of chromosomes i.e. 50% sperms have X and 50% have Y chromosome open from half the autosome (Meiosis). Therefore, the sperms are different with respect to the composition of sex chromosome. In case of humans, females are considered to be homogametic while males are heterogametic.
(ii) Yes, there are examples where males are homogametic and females are heterogametic. In some birds the mode of sex determination is denoted by ZZ (males) and ZW (females).
(b) As a rule the heterogametic organism determines the sex of the unborn child. In case of humans, since males are heterogametic it is the father and not the mother who decides the sex of child. In some animals like crocodiles, lower temperature favour hatching of female offsprings and higher temperatures lead to hatching to male offsprings.