Genetics

[Arty]

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

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!

[mith]

I think the answer for problem 1 is in problem 2 . 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.

[Arty]

I think the answer for problem 1 is in problem 2 . 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... )
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!

[mith]

Sorry I did my math wrong on the ratios but how can a female be XLY???

[biostudent84]

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.

[mith]

Well I was thinking explanation 2, but the male has two X's and the female has one?!

[biostudent84]

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

[canalon]

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

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


Patrick[/i]

[Arty]

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!!!!

[Arty]

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 . Now, I hope you're claryfied!!!!