Recombination Frequency Over 50%?

HotSoup

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10 years ago

If map units are representative of 1% possibility in genetic recombination, what about genes that are farther than 50 maps units away from the gene of interest? Would that mean that there is a guarantee of crossing over in such for all gametes? (Or illogically, more than all gametes? (Over 100%))

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Doctor-2-B

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10 years ago

No. RF would be the frequency per gamete. RF>50% means that there is a greater chance of crossing over than the parental genotype. I know how you're thinking about this, but it's incorrect. The RF is per gamete, not for the set (4 in humans). It's universal to all species, and some species don't produce 4 gametes during 1 meiotic cycle.

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HotSoup Author

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10 years ago

So for a large linkage map with two genes with, say, 75 map units apart, does that mean 3/4 of the four gametes will display recombinant rather than parental traits? How is that even possible?

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Doctor-2-B

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10 years ago

Let's say the parentals are AaBb x aabb. Without linkage, you'd get:
25% AaBb - parental genotype
25% aabb - parental genotype
25% Aabb - recombinant
25% aaBb - recombinant

Let's say we have a 98% RF (98 mu). This implies that any recombinant will occur 98% of the time. Therefore, each recombinant will occur 98%/2: 49% of the time. This will generate the distribution:
1% AaBb - parental genotype
1% aabb - parental genotype
49% Aabb - recombinant
49% aaBb - recombinant

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HotSoup Author

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10 years ago

Okay, I see.

How about genes that are greater than 100 map units apart?

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Doctor-2-B

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10 years ago

Well, my explanation was merely anecdotal, because the parental genotypes MUST be 50% or greater.

If the distance is >50mu, the genes are assumed to assort independently (i.e. not linked). As a further consequence, recombinants will never outnumber parental genotypes.

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HotSoup Author

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10 years ago

Okay, that makes perfect sense.
Thank you.

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Doctor-2-B

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10 years ago

Thrilled to help

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