Crossing Over

[Edher]

Saludos,

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?

Thank You,
Edher

[Poison]

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.

[lohita]

crossing over occurs during miosis in metaphase when chromosomes line up in the equitorial area.

[Edher]

crossing over occurs during miosis in metaphase when chromosomes line up in the equitorial area.

Saludos Lohita,

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.

Edher

[MrMistery]

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?

[Edher]

Never Mind

[biostudent84]

Crossing over occurs during Meosis I. During this time, the cells still are Diploids.

[Edher]

You're right, I forgot about Meiosis I. Let me correct it.

Edher

[Diana R]

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.
Thank you.