Genetics as it applies to evolution, molecular biology, and medical aspects.
Does crossing over always occur to a pair of nonsister chromatids of a homologous pair of chromosomes (tetrad) in the prophase of meiosis I? In other words, does crossing over always occur when a homologous pair gather during prophase of meiosis 1 or could they simply go on with meiosis without having to exchange sections of chromatids inbetween nonsister chromatids?
As much as I know, as long as tetrad formation occurs, (it always occurs in meiosis) going on meiosis without exchanging sections doesn't seem likely to happen.
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Actually, crossing over occurs during Prophase I of Meiosis when tetrads are form by pairing up homologues. Furthermore, I don't believe that was the original question.
What about the XY pair? I heard that crossing-over happens there, but it's really rare. However, i am not sure. Anybody got any info on that one?
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
Maybe you can help me with this problem:
You discover a Drosophila male that is heterozygous for a reciprocal translocation between chromosomes 2 and 3. Each chromosomal breakpoint is near the centromere, which is near the center of each of these metacentric chromosomes.
Draw a diagram showing how these chromosomes would synapse at meiosis.
I can not clearly imagine what is going on with crossover in this case.
I have a prof that says that crossing over in meiosis happens during metaphase 1. I asked her about this, pointing out the evidence that I had that said that crossing over happens during prophase 1. She says that the line between prophase and metaphase are obscure and that the actual event happens during metaphase. What does anyone have to say about this?
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