Explain sex determination in human beings.
How is sex determined in human beings?
Explain the mechanism of sex determination in human being
Sex determination in human beings:-
- In human beings, the chromosomal mechanism of sex determination is of the XX-XY type.
- In humans, the nucleus of each cell contains 46 chromosomes or 23 pairs of chromosomes. Of these, 22 pairs are of autosomes and 1 pair is of sex chromosomes.
- Females possess two homomorphic sex chromosomes, XX.
- Males contain two heteromorphic sex chromosomes, XY.
- Females are homogametic and produce only one type of egg, (22+X).
- Males are heterogametic and produce two types of sperms, (22+X) and (22+Y).
- During fertilisation, if the sperm containing X chromosome fertilises the egg having X chromosome, then the resulting offspring would be a female (XX).
- If the sperm containing Y chromosome fertilises the egg having X chromosome, then the resulting offspring would be a male (XY).
- The sex ratio produced in the progeny is 1:1.
- This chromosomal mechanism of sex determination is called heterogamesis. It may be male heterogamety or female heterogamety.
Sex Determination in human being:
a. Human diploid cell has 46 chromosomes, i.e. 23 pairs in each cell.
Out of these, 22 pairs of chromosomes are called autosomes and one pair of chromosome is called sex chromosomes.
They are X and Y chromosomes.
b. Every individual gets one set of chromosomes from his mother and one from his father.
A human male thus has 44 +XY chromosomes, whereas a female has 44 + XX chromosomes.
c. During gamete formation; meiosis or reductional division takes place and a gamete gets only one set of chromosomes and thus it is haploid.
e.g. Female gamete (ovum) 22 + X, Male gamete (sperm) 22 + X or 22 + Y.
When the male and female gametes unite to form a zygote, the chromosomes again become diploid.
d. Thus, the offspring gets the same number of chromosomes as his parents. Sex of the baby is determined by the nature of sperm (X or Y) that fertilizes the ovum. Thus, in human being, it is the male which determines the sex of the baby.
Determination of sex in human beings:
- In human beings, the male possess 44 autosomes and a pair of heteromorphic sex chromosomes, XY, while the female possess 44 autosomes and a pair of homomorphic sex chromosomes, XX.
- At the time of gamete formation, meiosis occurs.
- The male parent produces X-bearing and Y-bearing gametes or sperms. The female parent produces only X-bearing gametes or eggs.
- During reproduction, the combination of one X-bearing gamete from the male with one X-bearing gamete from the female results in offspring with the genetic constitution XX. The child produced is a female or a daughter.
- The combination of a Y chromosome from the male with one X chromosome from the female results in an offspring with genetic constitution XY. The child produced is a male or a son.
- The offspring produced are always in equal proportion, and hence, the chance of having a daughter or a son is 50%.