Question

The sex chromosomes of both male and female are respectively
a) YY, XX
b) YX, XY
c) XY, XX
d) All of the above

Answer 1

In human beings, sex determination is of XX-XY type. The females are homogametic whereas the males are heterogametic.

Complete answer:
In human beings, the nucleus of each cell contains 46 chromosomes or 23 pairs of chromosomes.
Out of these, 22 pairs are autosomes. Autosomes are responsible for the determination of body characters.
The remaining pair is of sex chromosomes. Sex chromosomes are responsible for the determination of sex.
In females, two homomorphic sex chromosomes are XX and in males the two heteromorphic chromosomes are XY.
Thus, the genotypes of human female and male are
Female: 46 chromosomes = 44 autosomes + XX sex chromosomes.
Male: 46 chromosomes = 44 autosomes + XY sex chromosomes.

Additional information:
Mechanism of sex determination:
During gamete formation, the diploid germ cells in the testes and ovaries undergo meiosis to produce haploid gametes (sperms and eggs). The homologous chromosomes separate and enter into different gametes.
The human male is heterogametic and produces two different types of sperms - one type of sperm which contains 22 autosomes and one X chromosome and one type of sperm which contains 22 autosomes and one Y chromosome.
The human female is homogametic and produces only one type of eggs containing 22 autosomes and one X chromosome
During fertilization, if X containing sperm fertilizes the egg having X chromosome, then the resulting offspring with XX chromosome is a female.
If Y containing sperm fertilizes the egg having X chromosome then the resulting offspring with XY chromosome is a male.

So, the correct answer is c. XY, XX.

Note:
The same type of sex determination is seen in Drosophila melanogaster, where the female has a pair of XX chromosome and the male has a pair of XY chromosome.