User101010
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Please help I don't understand:
Q:
a mutation in another gene at another locus gives rise to white-eyed flies. Red eye allele(R) is dominant to white eye allele(r). Student crossed a red eye with white eye and expected a F1 generation of red eyed flies, but results were:

Phenotype: Num offspring:
red eyed female. 27
red eyed male. 0
White eyed female. 0
white eyed male. 23

Student suggested reason for red eye and white eye was that red eye parent was heterozygous.
explain why this cannot be the correct explanation for the results.


The answers arefor 3 marks)
If red eye parent was heterozygous:
-there would be no differences between the sexes
-red eye makes and white eye females would occur
-1:1:1:1 ratio

Could someone please explain the answers for me please
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Lighfy
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(Original post by User101010)
Please help I don't understand:
Q:
a mutation in another gene at another locus gives rise to white-eyed flies. Red eye allele(R) is dominant to white eye allele(r). Student crossed a red eye with white eye and expected a F1 generation of red eyed flies, but results were:

Phenotype: Num offspring:
red eyed female. 27
red eyed male. 0
White eyed female. 0
white eyed male. 23

Student suggested reason for red eye and white eye was that red eye parent was heterozygous.
explain why this cannot be the correct explanation for the results.


The answers arefor 3 marks)
If red eye parent was heterozygous:
-there would be no differences between the sexes
-red eye makes and white eye females would occur
-1:1:1:1 ratio

Could someone please explain the answers for me please

Try drawing a Punnett square, assume that the female is heterozygous (Rr) and the male is homozygous recessive (rr). This is because there are no white-eyed females and no red-eyed males in the offspring.

Look at the different combinations, you can see that there is a 1 : 1 : 1 : 1 phenotypic ratio, and therefore red-eyed males and white-eyed females would be produced in the offspring.

If you need anything clarifying, please let me know (I'm quite bad at explaining things!)
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User101010
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(Original post by Lighfy)

Try drawing a Punnett square, assume that the female is heterozygous (Rr) and the male is homozygous recessive (rr). This is because there are no white-eyed females and no red-eyed males in the offspring.

Look at the different combinations, you can see that there is a 1 : 1 : 1 : 1 phenotypic ratio, and therefore red-eyed males and white-eyed females would be produced in the offspring.

If you need anything clarifying, please let me know (I'm quite bad at explaining things!)
Sorry I still don't understand, because if you were to cross Rr and rr, you'd end up with two Rr's and two rr's again so how is it it wrong or a 1:1:1:1 ratio. Also how can you tell between sex here 😭
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Lighfy
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(Original post by User101010)
Sorry I still don't understand, because if you were to cross Rr and rr, you'd end up with two Rr's and two rr's again so how is it it wrong or a 1:1:1:1 ratio. Also how can you tell between sex here ������
I understand what you mean by getting two Rr's and two rr's. Assume that the alleles are sex-linked. Therefore, the female (XX) is heterozygous. Try drawing a punnett square with the sex genes. You'll see it is a 1 : 1 : 1 : 1 ratio now. (The male is still homozygous recessive). If you still don't understand, I'll show you
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User101010
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(Original post by Lighfy)
I understand what you mean by getting two Rr's and two rr's. Assume that the alleles are sex-linked. Therefore, the female (XX) is heterozygous. Try drawing a punnett square with the sex genes. You'll see it is a 1 : 1 : 1 : 1 ratio now. (The male is still homozygous recessive). If you still don't understand, I'll show you
I don't mean to be so demanding, but would it be possible if you could show me please as I really am struggling to understand
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Lighfy
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(Original post by User101010)
I don't mean to be so demanding, but would it be possible if you could show me please as I really am struggling to understand
No problem, happy to help

This should hopefully explain things (sorry about the handwriting).

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User101010
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(Original post by Lighfy)
No problem, happy to help

This should hopefully explain things (sorry about the handwriting).

Image
Thankyou, you have been very helpful, the only part I now do not understand is: why does this mean there are no differences between the sexes
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Lighfy
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(Original post by User101010)
Thankyou, you have been very helpful, the only part I now do not understand is: why does this mean there are no differences between the sexes
I think it means that if the female was heterozygous, then both the males and the females could have either white or red eyes, instead of males just having white eyes, and females red eyes, like the table shows. (If that makes sense )
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User101010
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#9
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(Original post by Lighfy)
I think it means that if the female was heterozygous, then both the males and the females could have either white or red eyes, instead of males just having white eyes, and females red eyes, like the table shows. (If that makes sense )
Okay, Thankyou very much, I understand it now.
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