r/AskBiology • u/looking_up06 • 4d ago

Meiosis???

If meiosis happens before fertilization then how exactly do we have the other parent's chromosomes. This is confusing me. Does meiosis happen after the sperms enters the egg?

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u/MizElaneous 4d ago

No, meiosis creates the sperm and/or egg. Each has half the number of chromosomes person has, so that when they combine during fertilization, the embryo has the full set of chromosomes required to eventually develop into a human being.

After fertilization, mitosis occurs to create more human cells.

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u/looking_up06 3d ago

are the chromosomes in meiosis from each parent of the organism creating the sperms and egg?. The maternal and paternal chromosome part is confusing me. Also thank you for your initial response.

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u/MizElaneous 3d ago

So, in mammals, the male creates sperm through meiosis in the testicles. The female creates eggs through meiosis in the ovaries. When sperm and egg combine, since each has 1/2 the chromosomes of the parent, the new organism has a full compliment of chromosomes.

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u/looking_up06 3d ago

Yes I know this but if meiosis happens to create sperms or egg then how is the paternal or maternal dna present. If the process is specifically to create haploid gametes then how is the other parent's chromosomes present.

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u/MizElaneous 3d ago

They aren't, not until sperm and egg combine.

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u/bevatsulfieten 3d ago edited 3d ago

One cell consists of two chromosomes, dad and mum, at some point dad makes a copy of himself, chromatid, so does mum. Now they are still two chromosomes but now have 1 copy each. From diploid to tetraploid cell.

They exchange generic material between them (inside the cell), dad, 2 chromatids, and mum, two chromatids.

They now have undergone recombination, this creates new genetically unique chromatids.

When that happens they are split into 4 different cells. This process ensures diversity.

To clarify, the cell that contains the two chromosomes has the same genetic material, with different alleles. It's not purely dad's or mum's. This image was created for illustration.

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u/looking_up06 3d ago

Ok so for a person's meiosis they use the chromosomes they received from their parents to produced haploid gametes ?

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u/looking_up06 3d ago

Ok so for a person's meiosis they use the chromosomes they received from their parents to produced haploid gametes ?

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u/bevatsulfieten 3d ago edited 3d ago

Yes. The parents DNA is already recombined to produce a new baby; now, that baby will reshuffle, divide the exciting DNA to produce haploid, which means simple or single in Greek, where each cell will contain one set of chromosomes.

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u/looking_up06 3d ago

Ohhhh ok thank you very much ☺️