What are chromosomes?
Sperms and Ovas are sex cells.
We know that every cell contains nucleus.
Nucleus of cell contains thread like structures called chromosomes
These chromosomes carry genes and help in transfer of characters from parents to children
What are Sex Chromosomes?
We know that when Male sperm meets female ova, fertilized cell is produced
This cell has 23 pairs of chromosomes in its nuclei
Out of these chromosomes, two chromosomes X and Y are called sex chromosomes
They help to determine whether new born child will be a boy or girl
How is sex of baby determined?
Sex of an unborn baby is determined when the egg cells of the women gets fertilized by the sperm cells of man and pregnancy takes place.
Sex chromosomes are present in the nuclei of each cell
Male sperm has 2 chromosomes X and Y
Female egg has 2 chromosomes X and X
When both fertilize,
X Chromosome of Male + X Chromosome of Female → XX Chromosome of Zygote ( Female )
Y Chromosome of Male + X Chromosome of Female → XY Chromosome of Zygote ( Male )
So sex of child is dependent upon father not mother (as father has both X and Y chromosome, but mother only has X chromosome)
NCERT Question 8 (c) - Sex determination in the unborn baby.