(Solved) Th Morgan hypothesis Allele for the white color eye is only on the X chromosom?

namatullah

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10 years ago

Th Morgan hypothesis Allele for the white color eye is only on the X chromosom?

I am FSc student and i am confused while studying the topic of " Sex linked Inheritance in Drosophile"
I think alot but do not get the actual reason that why he (T.H Morgan) suppose that
1 " allele for the white eyed male and red eyed female were located on the x choromosome."
2 " the Y chromosome does not contain any allele for the red eye clour

I hope i would get good answers immediately from this forum.
Thanks i advace

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padre

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10 years ago

In Drosophila, white eyes is caused by a recessive allele (r) located on the X chromosome. The dominant allele (R) produces red eyes.

Suppose a white-eyed female mates with a red-eyed male. Knowing this, if the Rightwards Arrow

Male has 1 X and 1 Y chromosome, so if he has red eyes his genotype is RY
The female has 2 X chromosomes so if she has white eyes her genotype is rr
The cross is rr x RY. Males get their X from their mother and Y from their father so the F1 males will all be rY - white eyes.
Females get an X chromosome from each parent so their genotype will be rR, red eyes.
The next cross is Rr x rY. Males will be 50% rY and 50% RY, females 50% Rr and 50% rr.

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sci_expert

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10 years ago

The first evidence for sex linkage in a particular species was given by T.H. Morgan in 1910 in white-eyed mutant in Drosophila. When white-eyed male was mated with a red-eyed female the F1 flies were all red-eyed. F2 generation of it included 3: 1 ratio of red and white-eyed flies. But all white eyed flies of F2 generation were males only. When normal female of F1 is crossed with normal male 50% of males were white-eyed and 50% were red-eyed (Fig. 46.17). It shows that the recessive allele is expressed in male only.

Morgan explained it as the association of the gene on ‘X’ chromosome. Because male has only one X chromosome all characters present on it will be expressed. The mutant allele (white eye) of the male is transferred to the female (heterozygous). The hemizygous males obtain their X chromosome from their heterozygous mother only then they will be 50% red-eyed (w+) and 50% white eyed (w).

The female can be white-eyed (ww) only when both ‘X’ carry gene for it. When heterozygous female (w+) is crossed with white-eyed male (w) then white-eyed females can be obtained.

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namatullah Author

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10 years ago

hey guys, i mean to say that due to which reason he claimed that these alleles are located on the X chromosome instead of autosomal chromosome? Neutral Face

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Answer accepted by topic starter

duddy

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Th Morgan hypothesis Allele for the white color eye is only on the X chromosom?

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