Gamete Formation :
- Both gametes i.e. sperm and ovum are formed by meiosis.
- Sperms are produced in testes of men from beginning of maturation (puberty) till death.
- However, in case of women, at the time of birth, there are 2 – 4 million immature oocytes in the ovaries of female foetus.
- An oocyte matures and is released from ovary every month from the beginning of maturity up to the age of menopause (approximately 45 years of age).
- Menopause is the stoppage of functioning of female reproductive system.
- At the age of about 45 – 50 years, secretion of hormones controlling the functions of female reproductive system either stops or becomes irregular. This causes the menopause.
Fertilization:
- Formation of zygote by union of sperm and ovum is called as fertilization.
- Fertilization is internal in humans.
- Semen is ejaculated in vagina during copulation.
- Sperms, in the numbers of few millions start their journey by the route of vagina – uterus – oviduct.
- One of those few million sperms fertilize the only ovum present in the oviduct.
- From the age of puberty up the menopause (from 10 – 17 years of age up to 45 – 50 years), an ovum is released every month from the ovary.
- Out of 2 – 4 million oocytes, approximately only 400 oocytes are released up to the age of menopause.
- Remaining oocytes undergo degeneration.
- Oocytes released from ovaries during last few months nearing the age of menopause are 40 – 50 years old.
- Their ability of division has been diminished till now.
- Due to this, they cannot complete meiotic division properly.
- If such oocytes are fertilized, the new-borns produced from them may be with some abnormalities like Down’s syndrome.
+ Point:
- The chromosome number in germ cells producing the gametes are diploid i.e. 2n.
- It includes 22 pairs of autosomes and 1 pair of sex-chromosomes i.e. (44 + XX or 44 + XY)
- Due to this, gametes contain only haploid (n) number of chromosomes i.e. (22 + X or 22 + Y).
- Two types of sperms - (22 + X) or (22 + Y).
- Oocytes are produced of only one type - (22 + X).
- Both, sperms and oocytes are produced by meiosis.
- In case of sperms, process of meiotic division is completed before the sperms leave male reproductive tract.
- However, in case of oocytes, process of meiotic division completes after ovulation; during fertilization in oviduct.