How are chromosomes paired? Shape of Y chromosome?

[cliverlong]

Hi

Can someone clarify the following for me?

The human has 23 pairs of chromosomes in the somatic cells. What characteristic of the chromosomes result in them being paired? Do the same genes (but potentially different alleles of those genes) occupy the same position on the two pairs?

The human male has 22 pairs and an XY “pair”. What is the shape of the Y-chromosome? (don't say Y). I'm thinking that in the early stages of mitosis and meiosis (early prophase?) the chromosome replicates its DNA and both strands are linked by the centromere. If this is true, then surely every chromosome before it replicates is a single strand neither X nor Y shaped and when it starts to replicate, every chromosome is X-shaped. Is it that the X-Y pair actually are completely different sizes and that the centromere of the Y chromosome is so near one end of the chromosome that is appears X-shaped where it is actually X-shaped?

Thanks

Clive

[JackBean]

actually, it is kind of Y
http://www.in-gender.com/cs/blogs/gende ... mosome.jpg

[Darby]

Since chromosomes are only light-microscope-visible in their connected-duplicate form during cell division, that's when shape names are given. Otherwise they're spun out quite a bit and have all sorts of somewhat linear shapes.

[MrMistery]

what you said in your final paragraph is 100% correct, except at the end it should be "it appears Y-shaped where it is actually X-shaped" - which i suspect is what you meant, and you only made a typo