I want to be very clear, I am not saying that there is anything wrong with people with Down syndrome having or raising children. I am confused because I learn in high school biology that animals like mules cannot reproduce because of their odd number of chromosomes so why is this not true for humans with an odd number of chromosomes?
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This is a misconception. Animals with mismatched chromosome numbers can reproduce and have fertile offspring. Here’s a great comment explaining it:
>Just to be clear about this since it’s widely misunderstood: chromosome count has absolutely zero to do with whether two organisms are able to produce offspring together.
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>Homologous chromosomes never pair during fertilization or embryonic development, so the number is completely unimportant. What matters for producing offspring is molecular recognition between the gametes that allows for fertilization and gene regulatory interactions between the parent genomes in the zygote/embryo during development. These things are based on the *nucleotide sequences* in the genome, not how many chromosomes it’s made up of.
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>Chromosome pairing doesn’t come into play until meiosis, so it can affect the fertility of offspring, but not whether they’re produced in the first place. Those are two completely different things. The chromosome count alone still doesn’t determine anything, though, because more than two chromosomes can line up, forming a trivalent instead of a bivalent, and functional gametes can still produced even if chromsome numbers inherited from the parents don’t match. This only fails when the *nucleotide sequences* along the chromosomes are too different from one another, so it’s again about the sequence, not the number.
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>Even the sterility is not determined by chromosome count. The hybrid cross between a Przewalski’s horse and a domestic horse, which also have different numbers of chromosomes (66 vs. 64), are **not** sterile, for example. Meanwhile, the hybrid offspring of a Muscovy duck and mallard duck are healthy, but sterile even though the parent species have the same number of chromosomes. And of course a human and a Reeve’s muntjac can’t produce offspring together at all, sterile or otherwise, even though we both have the same number of chromosomes.
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>I think the example of mules is the main source of this misunderstanding, precisely because they’re so well known. It makes people think chromosome count is important, but it’s really not.
Full credit to u/yerfukkinbaws
[https://www.reddit.com/r/biology/comments/tfqvcj/ive_recently_come_across_macroevolutionnet_and_im/i0y3smm?utm_medium=android_app&utm_source=share&context=3](https://www.reddit.com/r/biology/comments/tfqvcj/ive_recently_come_across_macroevolutionnet_and_im/i0y3smm?utm_medium=android_app&utm_source=share&context=3)
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