Linkage

[sigle]

---

Members don't see this ad.

Hi can someone help me with this question.
Basically what I understand is this; two genes are said to be linked if the probability of inheriting them together is greater than 50%. We assume that recombination occurs randomly therefore genes that are closer together will be less likely to be separated during meiosis.

So here is the question.
A tall plan with curly leaves (TT/CC) was crossed with a dwarf plant with straight leaves (tt/cc). F1 were crossed with eachother to produce F2 with the following:
34 tall plants with curly leaves
4 dwarf plants with straight leaves
11 tall plants with straight leaves
12 dwarf plants with curly leaves
Based on these results, are the genes linked for plant height and leaf shape?
A. No, since recombination occurred
B. No, since the phenotype ratio is close to the expected ratio for this cross
C. Yes, since recombination frequency is less than 50%
D. Yes, since there are considerably fewer recombinant plants than expected.

Okay so when genes are unlinked the phenotypic ratio is 9:3:3:1 therefore its B. 34:12:11:4 is pretty much 9:3:3:1 but how much of a deviation would there be for it to be considered not 'unlinked' if that made any sense. I get that, but I dont know how I can cancel out the rest of the answers. Especially with regards to D. How can I find out recombinant number?

Help please .

 

[sigle]

I guess to add. I thought that the RF when less than 50% signaled that perhaps these genes were linked. I just figured out how to get the RF as 11+12/61=37% which is less than 50% so wouldn't that reveal it is indeed linked?

What am I missing here. 😕

 

[Phantastic]

This is an MCAT question?

 

[sigle]

Lol! Yes. Its probably more simple than I'm making it out to be so I do apologize if this has caused some raised eyebrows.

TPR exam.

 

[sigle]

Bump. Any takers? I'm worried about this question because I remember vaguely covering it in my MCAT book(s)

 

[Phantastic]

Okay so when genes are unlinked the phenotypic ratio is 9:3:3:1...

3+3=6

6/(9+3+3+1) = 37.5%, which is less than RF 50%, so your example must contradict itself since it's indeed linked, right?

But wait, 9:3:3:1 is what we expect from independent assortment...


I was an instructor for TPR for chem and o-chem. Sometimes they reference material outside the scope of what you really need to know in order to prepare you for a passage. I think you could figure this out with intuition based on how close it is to the expected frequency of unlinked traits.