Question

Heterogametic sex determination based on the number of sex chromosomes among the following are
A) XX-XO and XX-XY methods
B) ZO-ZZ and ZW-ZZ methods
C) XX-XY and ZW-ZZ methods
D) XX-XO and ZO-ZZ methods

Answer 1

Heterogametic sex determination is defined as a sex that has sex chromosomes that differ in morphology. It produces different types of gametes. In mammals and most other animals the male is the heterogametic.

Complete answer:

In humans the male has X and Y chromosomes so it is referred as heterogametic sex.
The females have two X sex chromosomes so referred as homogametic sex.
The ZW sex determination system is a chromosomal system of sex determination in birds, some fish, some insects and reptiles.
In this system the females have a pair of dissimilar ZW chromosomes that are heterogametic.
The males have two similar ZZ chromosomes that are homogametic.
In the ZW system the ovum determines the sex of the offspring while in the XY sex determination system the sperm determines the sex.
The heterogametic can result in reduced or absent meiotic recombination.
The homogametic sex has sex chromosomes that match and produce the same gametes.

Hence the correct answer is XX-XY and ZW-ZZ methods.

Note: The males are not always heterogametic. The females are heterogametic in birds, moths and fish. The chromosomal sex is determined at the time of fertilization.The chromosomes are the thread-like structures which are found inside the nucleus of plant and animal cells. Humans have 23 pairs of chromosomes. The 22 pairs are autosomes while 1 pair is of sex chromosomes.