Sex linkage in fruit flies and huntingdons disease

Authors Avatar by zeynep_merve10hotmailcouk (student)

In fruit flies the eye colour trait is determined by the sex chromosome. There are two sex chromosomes, X and Y; XX indicates the individual is a female and the XY indicates being male. The sex chromosome include other genes that determine other traits. When these genes are positioned on a sex chromosome, they are named as sex-linked genes. The eye colour gene for fruit flies are solely found on the X chromosome because it is much bigger in size when compared to the Y chromosome; therefore, the genetic information found on the X chromosome is much more than the Y chromosome.

As female flies have a double copy of the eye colour gene, one on each of the X chromosome and male flies have one copy of the eye colour gene on the X chromosome, therefore that one copy gene will show up whichever allele he inherits from the mother flies. It is known that red eye colour (R) is dominant to white eye colour (r).

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In the P generation red eyed male flies (XRY-) were crossed with white eyed females (XrXr). The outcome of the F1 generation were half male white eyed (XrY-) and half female red eyed (XRXr). These results were obtained because the mothers’ genes determine the male offspring’s eye colour; as the mother has both recessive, white eye colour alleles, the male offspring’s are 100% white eyed (XrY-). Whereas the female offspring’s are all carriers (XRXr) and the red eye colour allele, which was inherited from the father, shows up in all of the female flies because it is dominant although ...

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