Homologous Chromosomes? Down rabbit hole?

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Homologous Chromosomes? Down rabbit hole?

Post by PoincareConjecture » Sat Sep 23, 2017 10:59 pm

Sir Andrew- chromosomes? again---so to me it appears to me that Somatic Cells are organized into pairs of homologous chromosomes, that is 23 pairs in total for a grand sum of 46 chromosomes per cell---and the gamete cells on the other hand are not organized into pairs of homologous chromosomes, the pairing happens only after fertilization takes place and the Zygote's DNA can then be described as having homologous pairs of chromosomes----So quick Summary x2 "key" cells in the body Somatic cells and Gamete cells---Going back to the somatic cells for a second the 23rd pair is the sex chromosome ---- is this the chromosomes that will carry specific male and female traits in to be expressed phenotypically and by gender e.g after puberty hair on the chest for males and other changes that take place, these changes are derived from the 23rd chromosome on the Somatic cell right?---The gamete cell to me then appears like a clever way of carrying one set of chromosomes destined for the next "hybrid" somatic cells in the Offspring that arises following fertilization....do i have my ducks in row here?
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Re: Homologous Chromosomes? Down rabbit hole?

Post by NS_Tutor_Andrew » Mon Sep 25, 2017 7:36 pm

Hi PoincareConjecture,

That sounds about 98% right -- the only substantive thing that I would add is that the X chromosome actually contains many genes that are not involved in sexual differentiation/the expression of sexual dimorphism. In contrast, the Y chromosome is much smaller and is specialized in genes necessary for the differentiation of males. This is why you can have no Y chromosome (as is the case for roughly 50% of the population), but you have to have an X chromosome -- so called "monosomy Y" (where a zygote has a Y chromosome but no X chromosome) is a lethal nondisjunction.

Good luck and feel free to follow-up with more questions!
Andrew D.
Content Manager, Next Step Test Prep.
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