Does Crossing over occur between sister or non-sister chromatids?

Question

Does Crossing over occur between sister or non-sister chromatids?

Answer 1

Non-sister chromatids. If they were sister chromatids crossing over, they'd be giving each other the same info. Two non-sister chromatids give each other different info, which makes sense in Meiosis.

Lamictalfan is wrong because in Meiosis, you need genetic combinations, i.e. variations.

Answer 2

Sister: these chromatids have the same genetic string of loci, just not necessarily the same alleles.

If you had non-sisters crossing over, you'd mess up the genome.  You get, for example, an allele coding for blue eyes when the locus should be governing the presence of absence of the rhesus protein on your erythrocytes.  Bad.

Answer 3

non sister chromatids!!!

Answer 4

Crossing-over occurs between non-sister chromatids, since (prior to crossing-over) sister chromatids are genetically identical (i.e. one is a duplication of the other).  Therefore, if sister chromatids underwent a cross-over, no genetic variation would occur.

See the link below, if you want an illustration.

Answer 5

Both. The belief that only non-sister chromatids are involved comes from confusing the physical act of crossing over and the genetic consequence of recombination. Crossing over between sister chromatids does not lead to new gene combinations,

http://www.answers.com/topic/chromosomal...