Homework Help: Genetics recombination questions

sonyab523 · Mar 17, 2010

Confused on 2 questions here

If a recombination frequency between two genes is 1.5%, what is the distance between the genes in map units on the linkage map?

a. Impossible to determine, because the interference is not known.
b. 1.5
c. 3
d. 0.75

Recombination frequencies

a. arise from completely random genetic exchange.
b. are the same for all genes.
c. decrease with distance.
d. are the same for cis and trans heterozygotes.

I thought it was b for the first part a for the second part and but I'm wrong. Can someone explain?

sonyab523 · Mar 17, 2010

Sorry forgot to add my explanation

b. Each % frequency of recombination equals one map unit between the genes. So 1.5% recombination frequency = 1.5 map units apart will result in 1.5% recombination

a. It can't be (b), because genes are all distances apart; it can't be (c), because frequencies increase with increasing distance; it can't be (d), because the distance between genes is the same whether the alleles are cis or trans loci. So I thought it was a.

sonyab523 · Mar 18, 2010

Help help please.

nobahar · Mar 18, 2010

I'm not absolutely sure, but I'd probably agree with your answers.

sonyab523 · Mar 18, 2010

nobahar said: ↑

I'm not absolutely sure, but I'd probably agree with your answers.

I thought I was right but when I entered it into the system I was wrong. I'm sure the first part is right and I thought the second part was right but I guess not.

epenguin · Mar 18, 2010

I would probably agree too. It is a strange way of examining to ask which of four statements is correct. It seems to me though I am a bit rusty, that you have to a little bit psych what some of the questions mean, if it's any consolation.

sonyab523 · Mar 19, 2010

Well that can't be right since it's marked wrong. Anyone think it's c for the second part?

nobahar · Mar 19, 2010

I don't think it's C.
I did think it may be D is the recombination frequency was being dtermined by phenotype. But, this seems less likely when I came across the following: http://books.google.co.uk/books?id=...e&q=recombination frequency cis trans&f=false
(Page 114)

chemisttree · Mar 19, 2010

I was thinking D and C. D because as the loci become further apart (low recombination values) the probability of a second crossover increases and the recombination value is overestimated. The only value less than 1.5 is 0.75 (D). I don't know what is meant by "interference" in answer A but that could be correct as well.

Edit. you are right C can't be correct

sonyab523 · Mar 19, 2010

I finally found some material that helped. I got it right and the answer was D. Thanks guys for your help I really appreciate it.

nobahar · Mar 20, 2010

I've been talking about question 2.
For which one is the answer D? What did you arrive at for number 2?
The link I recommended explicitly states that trans and cis heterozygotes exhibit equal recombination frequencies.

sonyab523 · Mar 23, 2010

nobahar said: ↑

I've been talking about question 2.
For which one is the answer D? What did you arrive at for number 2?
The link I recommended explicitly states that trans and cis heterozygotes exhibit equal recombination frequencies.

D is the answer for the second question. So you were right.

nobahar · Mar 24, 2010

sonyab523 said: ↑

D is the answer for the second question. So you were right.

My apologies, I lost track of the question! Technically I wasn't right, the textbook was...:grumpy: