Chromosome questions. Including explaining crossing over and why they come in pairs. Explain.?

Question

is there a reason humans have 23 pairs of chromosomes?

what is the point if these pairs are exactly identical (not including the s*x chromosomes)?

when the chromosomes look like Xs and are composed of sister chromatids, is that when they are actually called chromosomes, and the actual chromatids are never called chromosomes unless they are with their sister chromatid?

if there are 46 chromosomes are there 92 chromatids?

whats the difference between a centromere and a kineticore?

During crossing over, if the chromosomes cross over with thir homologous chromosome, dont they cross over with the same exact duplicate making crossing over pointless?

does cytokinesis occur in meiosis?

Thank you very much to some one who can answer these

Answer 1

We have 23 pairs of chromosomes because that is what is needed to carry all of our information.  It may seem redundant to have pairs, since each chromosome in a pair has the same information (minus the s*x chromosomes), but it helps give greater variability, and there are disorders when one of a pair is missing (like Turner's Syndrome where females are missing one of their X chromosomes), so it seems that sometimes two copies of a gene is needed to perform correctly.

The pairs are not identical, they carrier similar information.  Identical chromosomes will carry the same traits in the same locations, but the allele may be different.  That is why someone can be a carrier or have both the dominant and recessive form of a trait.

Okay, chromosomes and chromatids can get confusing.  When a chromosome has replicated and is still attached, it is composed of two sister chromatids, but once they separate each individual chromatid is then referred to as a chromosome. So chromatids are only present when a chromosome is copied and attached.

You could refer to it has having 92 chromatids, but only before they separate.  I have never heard it said that way, and if it is easier for you to think of it that way go for it, but I wouldn't make it a habit to refer to them like that.

The centromere is where the two sister chromatids are attached, and the kineticore is where the microtubles attach and pull them apart.

So with crossing over, the chromosomes are not identical, but carry that same trait information, so crossing over leads to greater genetic variability while still keeping all the information present.

Cytokinesis is the actual process of the cell splitting, so yes, it does occur in meiosis.

I hope this helps!