Annie.k
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Report Thread starter 8 months ago
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hi
im a bit confused with meiosis because :
in interphase homologous chromosomes replicate, so say the pink chromosome for hair colour replicates and the blue chromosome for hair replicates (i know its a gross oversimplification but just for this questions sake)
and then the homologous chromosomes for eye colour replicate, so lets say yellow and red
and now we have four chromosomes , two homologous for eye colour and two homologous for hair colour.
what i dont understand is when they are replicated and divide during meiosis one, obviously one of the homolous pairs ends up in one cell and the other in another. so for example the pink and red end up in one and the yellow and blue end up in another. if the cell is essentially meant to be identical at this point how does this work? because you've lost one of the chromosomes
im not sure if im just misunderstanding
thank you for anyone who replies
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OxFossil
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Report 8 months ago
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(Original post by Annie.k)
hi
im a bit confused with meiosis because :
in interphase homologous chromosomes replicate, so say the pink chromosome for hair colour replicates and the blue chromosome for hair replicates (i know its a gross oversimplification but just for this questions sake)
and then the homologous chromosomes for eye colour replicate, so lets say yellow and red
and now we have four chromosomes , two homologous for eye colour and two homologous for hair colour.
what i dont understand is when they are replicated and divide during meiosis one, obviously one of the homolous pairs ends up in one cell and the other in another. so for example the pink and red end up in one and the yellow and blue end up in another. if the cell is essentially meant to be identical at this point how does this work? because you've lost one of the chromosomes
im not sure if im just misunderstanding
thank you for anyone who replies
I'll try , but tbh your pink and red and blue stuff really confuses me, so I'll avoid that!

Prior to DNA replication, you have one paternal chromosome and one maternal chromosome, which are homologues ie they carry the same genes (but not necessarily the same alleles for those genes) in the cell. Total DNA complement in each cell is 2n

Replication occurs in prophase 1, doubling each chromosome into 2 identical chromatids., and doubling the amount of DNA in the cell to 4n

The doubled paternal and doubled maternal chromosomes align so that similar DNA sequences from the paired chromosomes line up and can cross over one another (recombination). This produces 4 'new' chromatids, each with a mixture of alleles from the maternal and paternal chromosomes. But wWe still have a cell with 4n amount of DNA.

In anaphase 1, the 2 'new' homologous chromosomes (each one made up of 2 recombinant chromatids) are pulled to opposite poles of the cell. ie 1 of the 'new' doublets goes to one pole and the other goes to the other pole.

The cellular machinery always 'knows' these are homologous chromosomes and that one must go to one pole and the other must go to the opposite pole. This is true for each chromosome pair, so that means each daughter cell will have a full complement of chromosomes, and 2n of DNA in total.

When the second round of division happens, the chromatids are split so that each gamete cell has 1 chromatid from each chromosome (1n) - but they still have the full range of chromosomes. On fertilisation, the zygote gets 1 chromatid from the father and 1 from the mother, so you are back to a 2n cell.

Hope that helps
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Annie.k
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Report Thread starter 8 months ago
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(Original post by OxFossil)
I'll try , but tbh your pink and red and blue stuff really confuses me, so I'll avoid that!

Prior to DNA replication, you have one paternal chromosome and one maternal chromosome, which are homologues ie they carry the same genes (but not necessarily the same alleles for those genes) in the cell. Total DNA complement in each cell is 2n

Replication occurs in prophase 1, doubling each chromosome into 2 identical chromatids., and doubling the amount of DNA in the cell to 4n

The doubled paternal and doubled maternal chromosomes align so that similar DNA sequences from the paired chromosomes line up and can cross over one another (recombination). This produces 4 'new' chromatids, each with a mixture of alleles from the maternal and paternal chromosomes. But wWe still have a cell with 4n amount of DNA.

In anaphase 1, the 2 'new' homologous chromosomes (each one made up of 2 recombinant chromatids) are pulled to opposite poles of the cell. ie 1 of the 'new' doublets goes to one pole and the other goes to the other pole.

The cellular machinery always 'knows' these are homologous chromosomes and that one must go to one pole and the other must go to the opposite pole. This is true for each chromosome pair, so that means each daughter cell will have a full complement of chromosomes, and 2n of DNA in total.

When the second round of division happens, the chromatids are split so that each gamete cell has 1 chromatid from each chromosome (1n) - but they still have the full range of chromosomes. On fertilisation, the zygote gets 1 chromatid from the father and 1 from the mother, so you are back to a 2n cell.

Hope that helps
That cleared it up ! Thank you so much !
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