Why are gametes haploid and not diploid?

Do gametes need to be haploid or diploid?  Why?

Gametes are always haploid. Gametes should be haploid for maintaining the chromosome number of the species.This is achieved by meiosis the reduction division in germ cells.

Meiosis is reduction division that occurs only in germ cells where gametes are produced with half the chromosome number to that of the parent cell.

In humans, the production of male gamete takes place in the testes. In the testis, a diploid  spermatogonium (2n chromosome number=46) undergo meiosis, producing 4 haploid sperm cells (1n chromosome number=23).

In females, the production of gametes takes place in the ovary. Here, a diploid  oogonium (2n chromosome number=46) undergoes meiosis to produce a single large ovum or egg and 3 smaller polar bodies that normally disintegrates.

Human life cycle

Let us take the example of ours
  • Chromosome number=46 (diploid)

As a result of meiosis in germ cells:
  • Egg 23 chromosome (haploid) + Sperm 23 chromosome (haploid) = Zygote 46 chromosomes (diploid)

In egg and sperm, there is only one copy of a gene. That is why it is haploid.
  • The resultant zygote 23 + 23 = 46 chromosomes (diploid) 23 from the father's sperm and 23 from the mother's egg.

Each chromosome is represented twice that is why we call its as diploid.

If chromosome number is not reduced by meiotic division. Then
  • Egg 46 chromosome (haploid) + sperm 46 chromosome (haploid) = Zygote 92 chromosomes (tetraploid)
Chromosome number changed in a species and can be disastrous.


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