Question

How many chromosomes are found in human ovum?
a) 46
b) 64
c) 23
d) 32

Answer 1

Hint: Human ovum is the female gamete. Gametes are formed by gametogenesis. Spermatogenesis forms sperms and oogenesis forms ovum. The ovum fuses with the sperm and thuis zygote is formed that undergoes further development to form embryo and then foetus.

Complete answer:
Sperms are formed by spermatogenesis and ovum is formed by oogenesis. The stem cells are the major pre-requirements for these processes. The main difference between the two processes is that oogenesis is an unequal division.

>Oogonia are the mother cells that start the process. These cells are formed in yolk sac but migrate to the gonads. These are diploid cells (2n=46).
>These cells undergo Mitosis to form Primary oocytes. Mitosis is equational division. Thus primary oocytes are also diploid.The Primary oocytes then undergo Meiosis 1 and form one secondary oocyte and first polar body. Meiosis 1 is reductional division. Hence the daughter cells are haploid (n=23).
>The secondary oocyte undergoes Meiosis 2 to form ovum and second polar body. (This process takes place only when sperm enters the egg). Meiosis 2 is also equational division and thus the ovum is haploid (n=23).

Hence the correct answer is option ‘c’.

Note: Humans show 46 chromosomes ( 23 pairs). The gametes are always haploid so that during fertilisation when the gametes fuse, the zygote is diploid and thus the ploidy level is maintained.