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Meiosis - Altius 10 COVID - Question 48 BB section
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Josh_4080
#1 Posted : Thursday, July 30, 2020 7:07:50 PM
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For question 48, it states that this is an insect with 8 chromosomes. Should we have 8 chromosomes left after meiosis, not 4? For example, we have 23 chromosomes, and 23 pairs of chromosomes. At the start of meiosis we have tetrads (4n) and then result in dyads, and then result in just n. Right? So we start with 23 chromosomes and end with 23 chromosomes?

Thanks!
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INSTR_Katerina_102
#2 Posted : Tuesday, August 04, 2020 10:37:02 PM
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Hi Josh,

I've attached a worked solution to this particular problem here:

https://alumniubcca-my.s...t2GPirJ5ocD2L4g?e=Upos1Y

Please not that for the second meiotic division, I have not lined up my sister chromatids properly (they should be like those on answer A in the altius). I apologize for this error.

For humans, we do have 23 chromosomes. However we have 23 pairs of chromosomes, for a cellular count of 2n = 46 for a cell that has gone through S phase.

At the start of meiosis, we should have 2n = 46 chromosomes.

Following the first telophase, homologous chromosomes seperate, not sister chromatids, so you have n = 23 chromosomes, with sister chromatids attached.

Following this, you have the seperation of sister chromatids, and finally gametes are formed with half of the homologous chromosomes available.

So as a result, a fly with 8 chromosomes will have 4 chromosomes in each of its gametes following meiosis, and A shows this ongoing final mitoticdivision into 2 gametes.

Please let me know if this is unclear.

Katt
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