Biology/Genetics Question

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15+ Year Member
May 1, 2008
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The question asks what is the earliest point in meiosis at which a scientist can deduce with certainty the nucleotide sequence of the third chromosome of each gamete?

- prophase I
- metaphase I
- prophase II
- telophase II

Solution: prophase I, because the only change that can occur to the nt. sequence will be during crossing over. Crossing over occurs in prophase I.

The solution seems to lean towards a recombination based answer.

Is it possible to look at it genotypically? I was thinking that each chromosome in prophase I has its unique alleles, which between the two homologous chromosomes are likely to be quite different.

This would mean that the scientist is not able to deduce the nt. sequence of chromosome 3 in each of the gametes after prophase I.

The answer that I was leaning towards was prophase II, because then then the homologous chromosomes have already split so each individual gamete's nt. sequence can be determined with certainty.

This question may be a bit confusing because I guess the question is assuming that the homologous chr. are identical. I also guess that the gametes that are produced are considered unordered and ignoring the alleles and order... prophase I would be correct I guess.

Any comments?

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Awesomeness Incarnate
10+ Year Member
15+ Year Member
Dec 3, 2007
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prophase I makes sense because after prophase I no recombination takes place. since no recombination takes place, the nucleotide sequences are not going to change. so the scientist will be able to determine the nucleotide sequence. I think you were over-thinking the question.:D