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Genetics

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Genetics

Postby Arty » Tue Apr 12, 2005 1:46 pm

Can you solve the following problems(I'm sorry if I haven't found the right terms,hope you understand me :wink: )

Problem 1
From the cross-breeding of a pair of vinegar flies (Drosophila melanogaster) there are obtained 420 offspring, from which only 141 are male. How can you explain such a fact?

Problem 2
At hens does exist a lethal gene recessive on the L sexual chromosome. Which would be the ratio of sexes in the offspring derived from the cross-breeding of a cock heterozygote for this trait with a normal hen?

Regards

PS: Need the answers before Thursday!! Thanks for the understanding!
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Postby mith » Wed Apr 13, 2005 8:59 pm

I think the answer for problem 1 is in problem 2 :D. Since the males are around 1/4, I'm guessing there's a lethal sex-linked gene.

On question 2, I don't think males can be heterozygote for sex-linked traits. They either have the trait or they don't.
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Postby Arty » Thu Apr 14, 2005 1:07 pm

mithrilhack wrote:I think the answer for problem 1 is in problem 2 :D. Since the males are around 1/4, I'm guessing there's a lethal sex-linked gene.

On question 2, I don't think males can be heterozygote for sex-linked traits. They either have the trait or they don't.


That's all you can do?What a pity!(...I'm joking... :lol: )
Hey listen here, guy:
Problem 1
We have 141 males and 279 females.So the phenotypic ratio is 1:2.In fact we expected to get the ratio 2:2.
Reasoning and doing the Punnett net we get XAXA, XAXa, XAY, XaY.Males with the last genotype do not live.So there must be a lethal gene a in the chromosome X of the males.That's the explanation!!

Problem 2
Doing the cross-breeding of a male( XLXl) with a female (XLY) we get the ratio 2(males):1(female).

Ciao!
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Postby mith » Thu Apr 14, 2005 8:17 pm

Sorry I did my math wrong on the ratios but how can a female be XLY???
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Postby biostudent84 » Thu Apr 14, 2005 8:19 pm

Reading back on the post, I think he meant one of two things...

1. There is a third sex chromosome called "L" and I don't know about it ;)

or

2. He meant X^L as a gene on the X chromosome.
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Postby mith » Thu Apr 14, 2005 8:25 pm

Well I was thinking explanation 2, but the male has two X's and the female has one?!
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Postby biostudent84 » Thu Apr 14, 2005 9:24 pm

Arty wrote:Doing the cross-breeding of a male( XLXl) with a female (XLY) we get the ratio 2(males):1(female).


He shows the male as having two X's, and the female having an X and a Y...looks like it might be a mistake...I've made worse ;)

But only he can clarify
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Postby canalon » Fri Apr 15, 2005 1:20 pm

biostudent84 wrote:
Arty wrote:Doing the cross-breeding of a male( XLXl) with a female (XLY) we get the ratio 2(males):1(female).


He shows the male as having two X's, and the female having an X and a Y...looks like it might be a mistake...I've made worse ;)

But only he can clarify


:idea: I just checked google to clear up a few older memories on sex determination in birds, and as I thought Arty is not making a mistake.
In fact sexual chromosomes in birds are called Z and W and the malle is ZZ and the female ZW.
Hence male heterozygote should be written Z^L/Z^l (l for the male lethal form, L for the normal form of the gene) and the female Z^L/W

Good luck with the squares, I've got to take care of my E. coli
8)

Patrick[/i]
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Postby Arty » Sun Apr 17, 2005 5:02 pm

Canalon wrote: I just checked google to clear up a few older memories on sex determination in birds, and as I thought Arty is not making a mistake.
Patrick[/i]


Finally one who knows what we are talking about!!!! 8)
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Postby Arty » Sun Apr 17, 2005 5:05 pm

biostudent84 wrote:He shows the male as having two X's, and the female having an X and a Y...looks like it might be a mistake...I've made worse ;)

But only he can clarify


Hmmm I was absent these days, so I couldn't guess what great ideas you were posting . :lol: Now, I hope you're claryfied!!!! 8)
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