Genetics Question

Chucky

Hey

I have an answer to this question but am not confidant with my answer so I want to know what other people get. Here it is:

"In Drosophila melanogaster, straight wings (S) are dominant over curled wings (s) and long bristles (L) anre dominant over shaven bristles (l). Both traits are autosomal and segregate independently.

If flies of the genotypes (SsLl) and (ssLl) were to mate, what kinds of offspring would they produce and in what ratio?"


Now, I have written the parents' genotypes as SL/sl X sL/sl. is that correct? ...and will recombinations occur?


Thanks

Chucky

I think I have it now. Here is what I got:

Straight Winged & Long Bristles - 9
Straight Winged & Short Bristles - 1
Curled Wing & Long Bristles - 6
Curled Wing & Short Bristles - 4


Therefore a 9:6:4:1 ratio. To arrive at this I used the idea that recombinations among genes occures in 20% of the gametes.

Vangelis

How did you find that out?

DrIndy

Correct my genetics which I have not done in depth for a few years, but I come up with 6 StraightLong, 2StraightShort, 6CurledLong, 2CurledShort.

The question does not mention recombination - and the two genes are autosomal dominant/recessive segregate independently.

Chucky

...I'll try to get back to ye with the correct answer when I find out tomorrow.

GuanYin

Dr Indy has it right.

---

sL

---

sl

---

sL

---

sl
SL--SsLL---SsLl---SsLL---SsLl
Sl--SsLl---Ssll---SsLl---Ssll
sL--ssLL---ssLl---ssLL---ssLl
sl---ssLl---ssll---ssLl---ssll

6:Straight Winged & Long Bristles
6:Curled Wing & Long Bristles
2:Straight Winged & Short Bristles
2:Curled Wing & Short Bristles

Vangelis

How do you find the probability of getting any of them?
That's a stupid question, but it would really help me as I'm preparing for a biology exam.

Is it 6,25%?

GuanYin

Vangelis wrote:

How do you find the probability of getting any of them?
That's a stupid question, but it would really help me as I'm preparing for a biology exam.

Is it 6,25%?

Avoiding genetic terminology.......

SsLl and ssLl are the parents

SL, sL, sL and sl are the possible contributions from parent 1

sL, sL, sl and sl are the possible contributions from parent 2

(crossing the two genotypes)

create a table cross thing the 4 contributions from each as above.

Work out the ratios of phenotype.

Vangelis

psi wrote:

Avoiding genetic terminology.......

You can use genetic terminology.

SsLl and ssLl are the parents

SL, sL, sL and sl are the possible contributions from parent 1

sL, sL, sl and sl are the possible contributions from parent 2

(crossing the two genotypes)

create a table cross thing the 4 contributions from each as above.

Work out the ratios of phenotype.

Thanks.

Chucky

Psi, that is actually incorrect. The correct gametes produced will be:

SsLl -> SL, Sl, sL, sl

ssLl -> sL, sl

The correct answer to the question is here:

http://www.geocities.com/kev_blighe/Genetics.jpg

Really, I don't know why I couldn't do the question in the first place. It's just a straightforward cross. The wording of the question fooled me.

Vangelis

Is this dihybrid?

GuanYin

Chucky wrote:

Psi, that is actually incorrect. The correct gametes produced will be:.

Ermm I typo'd in my answer to vangelis but the workthough before hand is correct.

The rations 3:1:3:1 are the same as 6:2:6:2 and you would have gotten the same marks had you done it either way.

Chucky

Vangelis wrote:

Is this dihybrid?

Yeh simple di-hybrid cross.