Really confused. How many chromosomes pairs do humans have in their sex cells? How many single chromosomes do humans have in their sex cells?

  • 1
    $\begingroup$ Human sex cells, or gametes, have 23 chromosomes - they are haploid. Somatic cells are diploid - they have 23 pairs of chromosomes, for a total of 46. $\endgroup$
    – MattDMo
    May 5 '16 at 13:16
  • $\begingroup$ To add on @MattDMo's comment, each chromosome can be made of a single or two chromatids depending on the phase of the cell cycle you are in. $\endgroup$
    – Remi.b
    May 5 '16 at 22:11

Terminology is what is holding you back. What chromosome implies depends on context, i.e. is it replicated or not.

In Meiosis. Gametes arise from Germline cells that have 23 PAIRS of chromosomes. That means, that while there are 23 different chromosomes they come in doubles/pairs. This is the typical X like shape we think about when we hear chromosomes.
Another way, chromosome can means either 1X or 2 single chromatid

MEIOSIS I -- 23X chromosome pairs are duplicate and end up as 46X chromosome pairs (46 pairs of X OR, 92 separate chromatid)

These 46X are divided equally among two daughter cells just like in mitosis. Where now each daughter cell receives 23X = 23 pairs.

MEIOSIS II. The daughter cells in end of Meiosis I divide without DNA replication and the 23 pairs are split among 2 new cells. So now each new daughter cell (in total 4) has 23 individual chromatid (individual chromosomes) and these are the gametes.

When the gametes fertilize to form a zygote, the zugote product ends up 24X each.

Each X contains, 1 chromatid (|) from the father and 1 chromatid {|} from the mother.

Haploid means once copy of each chromosome. 23 Diploid means two copies chromosomes or 23X

Ref - Allison Q.N,.(2015), Freeman Biological Science.

  • 1
    $\begingroup$ Gametes have 23 PAIRS of chromosomes. No. Gametes have 23 chromosomes - they are haploid. Somatic cells are diploid - they have 23 pairs. $\endgroup$
    – MattDMo
    May 5 '16 at 13:13
  • $\begingroup$ Cheers MattDMo cleared it up. $\endgroup$
    – SciEnt
    May 5 '16 at 17:24

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