I am totally new to biology and I have a very stupid question. In the typical representation of meiosis, haploid cells contain two different chromosomes, resulting from the crossing-over process. But diploid cells have two homologous copies of each chromosome, usually one from the mother and one from the father. So, since there are two identical copies of the same chromosome for each parent, it means that each haploid cell brought only one out of two chromosomes into the zygote. My question is: how is this chromosome selected? Is it a combination of the chromosomes contained into the haploid cell? Is it one of the original two, while the other one is discarded in the fertilisation process?

I'm sorry if my question is not clear. Thanks.

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    $\begingroup$ Have you looked at Meiosis II, the second part of the process? $\endgroup$
    – Bryan Krause
    Jul 14 '20 at 15:08
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    $\begingroup$ I am not sure about where is your confusion. Do you understand that homologous chromosomes are represented as having same size in the image? So the chromosomes in doughter niclei II are definitely not homologous? $\endgroup$
    – BagiM
    Jul 14 '20 at 16:28
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    $\begingroup$ Thank you guys. I think that my confusion about this representation arises from me thinking that the two same-color chromosomes in the first diploid cell were identical. I hadn't noticed the difference in size. So let us take the first haploid cell from above. The longer chromosome will be the homologous chromosome of the same-size one coming from the other gamete? (The same for the short one) $\endgroup$
    – Luigi
    Jul 14 '20 at 19:08
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    $\begingroup$ @Luigi Yes, I think that they usually include more than one non-homologous chromosome in the models to remind us that most (all?) organisms that do meiosis have >1 chromosome in their genome (e.g. humans have 23 chrs in the haploid state). So it's always super important to sort out homologous vs. non-homologous chromosomes before you do anything. $\endgroup$ Jul 14 '20 at 19:40
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    $\begingroup$ @Luigi Since you were also confused about the colors: The same colored chromosomes represent chromosomes coming from the same parent. So for example red chromosomes came originally from mother and gray from father. Thay do this to show that after crossover there are "mixed" chromosomes - patchwork from both parents. $\endgroup$
    – BagiM
    Jul 15 '20 at 4:24

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