Human chromosomes

[active]

Hi!
I was reading an article about human cell structure and I got curious about one thing.
Why do we (humans) have 2 chromosomes of the same kind. I mean 23 pairs. Why we don't have 46 different chromosomes?

[JackBean]

There's difference between having 23 chromosomes/pairs of chromosomes and have 46 chromosomes. So the question is, why do we have 46 chromosomes (23 pairs) instead of having only 23.
Also, this question applies only to somatic cells (the cells of your body) and not to germ cells (eggs and sperms).

[active]

Thanks, but I was wondering why do we have 2 of the same kind? Also, then what is the difference between having paired chromosomes and not?

[mith]

they're not the same. as jack was alluding to previously, you should investigate sperm and eggs.

[plasmodesmata11]

because if you had one copy of each chromosome, how could you have sex cells???

[jwalin]

basically for reproduction

[active]

Thank you all! Now I know my mistake, sorry about that! Maybe now I can rephrase my question:
Then why do our chromosomes are paired? As I know now, they are different , but why 1st chromosome pair contains of 2 chromosomes (I know, because it is a pair ) and not for example 3 or 4?

[JackBean]

because if you had one copy of each chromosome, how could you have sex cells???

active: also, how would you get 3 or 4 chromosomes from 2 parents?

[JackBean]

also, our genome has size of ~3 Gbp, that is, you use ~3giga ATP-equivalents only in the body of DNA (not mentioning the process of building), so have more DNA would be quite energetically demanding

[mikemd]

are the X and Y chromosome homologous like the autosomes?

[Swede]

No.

One main reason to why we have chromosome pairs is that they compensate for inadequate qualities of one. That's why persones with very alike genome (like siblings) often produce children with diseases due to a short variation of genes. Some genes are also transcripted from both alleles on both chromosomes in one pair, giving a variety which in many cases gives the individual advantages.

[jwalin]

i thought that x and y are homologous
atleast in a karyotype we see so
and another thing for proper reproduction they should be homologous