recombination frequency

[zinjanthropus]

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can somebody remind me how to calculate linkage and recombination frequency?

i know it has something to do with counting the progeny that do not resemble either of the parental generation, but i can't quite remember what to do after that....

thanks for any help

 

[PreMedAdAG]

recombinations frequency = # of recombinants (ones that don't look like parents or weird numbers) divided by # of total progeny

so. 400 progency
100 recombinants

Recombination frequency = 100/400

25% (that' really high, but whatever you get the idea)

25 also equals the number of map units that the two alleles are apart from eac other on the same gene.

 

[zinjanthropus]

thanks for the response...

that makes sense but i guess my problem is actually identifying the recombinants

for example if i were looking at 2 genes and i crossed two individuals that were heterozygous for those genes
then AaBb X AaBb should give me a 9:3:3:1 ratio of A-B-, aaB-, A-bb, and aabb......right?

so are the recombinants all of those progeny that are not AaBb?

 

[Deepak_nc]

all recombinants = everything minus parental types...( the 2 plants that you cross)

 

[PreMedAdAG]

If it's a 9:3:3:1, then it's typical Mendelian ratio... but here's the thing:

If you got something like 11: 9: 1:1 then you would see that the 1's would be the recombinants. Usually those mendelian ratios means that the two traits are inherited together, but that they aren't linked. So in other words..

Tall = T
Short = t
Yellow = Y
white = y

when you do the cross, you should get a 9:3:3:1, unless they are linked. If linked, you won't get this clean ratio.

Here's another way to think about it.
For a linked trait:
Draw out two vertical lines ---A------Y---- Parent 1 (AAYY)
---a------y---- Parent 2 (aayy)
if the kids end up with like:
------a----Y-----
or
-----A-----y-----
Then those are the recombinants because they don't like look either of the parental combinations.. so in other words.. if the progeny look like a parental cross, then probably not linked, but if they look like something else other than that, then the genes may be linked. If all else fails, just look for weird ass numbers.. that usually works.. sorry that was so confusing, kind of hard to draw on SDN

 

[zinjanthropus]

okay, i think i've got it now....thanks!

 

[amy73]

HI

The way that works the best for me... is to see which ones are the most in number.. those are parents.. everything else is recombinant.. the least frequent are the ones with more recombinance..

Most of the time u will be given the genotypes of the parental alleles.. so if u can identify the singel and double cross over recombinants.. then u can easily calculate the sequence of the genes.. and map distance and so on..

Good luck

Amy

 

[Childe]

I doubt the mcat would require this knowlege without a passage.

 

[Persistence101]

Originally posted by Childe
I doubt the mcat would require this knowlege without a passage.

thank goodness!





Anyhoo, what is the significance of a double crossover? Can someone please explain this? Thanks.