Biology Question

Hopefully there will be someone here who can explain this to me as I haven't been able to find a book that does.In reproduction the sperm and the egg cell join to form an embrio. Each gametes cell countained half the number of chromosomes thereby giving the emrio a full set as it were. Here is where my lack of knowedge comes in. During meiosis how is the chromosome split? Is it down the middle, kinda like each side of a zipper?If this is the case you should then be left with half (ie left or right for the lack of a better term) of a DNA strand. Lets say that the egg cell contained the following strand:ATGTGCATCAThe sperm contained this corresponding strand:ATTAGCATCANow, if I am correct so far and I am right in saying that adenine and thymine always bond together, and guanine and cytosine always bond together (i.e. your base pairs).I can't see how these combine, adenine won't bond with adenine etc. Also the second strand differs slightly from the first, a mutation if you will, how does this come into play when the two strands attempt to join.Could someone please explains this to me. I am fairly sure that I am missing or misunderstanding something here which is why I can't picture the joining of the egg and sperm cells once you move lower than the chromosome level.------------------
compmage

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[This message has been edited by compmage, 06-20-2002]

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Originally posted by mark24:

Put differently, you have two copies of chromosome 20, both are different. The splitting/copying of the chromosomes occurs in the parents, not during fertilisation.

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I was aware of this. I only just realized that the way the question was put made it sound as though I did not know that the splitting takes place in each parent.From your explanation I realise that my mistake came from thinking that the DNA itself split to form an egg or sperm cell, this was then causing me problems when I tried and join the egg and sperm cells in my mind and combine the half DNA strands. Thanks for the clarification.These things happen when you didn't take biology after std. 7 (grade 9) and even that was a decade ago. ------------------
compmage

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Originally posted by Quetzal:
compmage: the chromosome "splitting" (which is kind of a misnomer) takes place during the creation of the gametes - before fertilization. Here's a link to a pretty good, and relatively easy to understand, explanation. IOW, you don't have to worry about lining up base pairs - what gets separated are the two pairs of chromosomes. The chromatids aren't actually cut up. (See also "crossing over").

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[This message has been edited by Quetzal, 06-20-2002]

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Thanks. I do think 'splitting' is what put me on the wrong road here.------------------
compmage