Sex linkage in fruit flies and huntingdons disease

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 they receive a white eye allele from the mother.

Following from the F1 generation, according to the Punnett square findings 25% of the male offsprings, in the F2 generation, are expected to have white eyes (XrY-) and 25% have red eyes (XRY-); 25% of female offsprings have white eyes (XrXr) and 25% have red eyes (XRXr). As the males can inherit only one eye colour allele, which is from the mother and she had both dominant (XR) and recessive (Xr) eye colour alleles, 50% showed up as white eye colour and 50% showed up as red eye colour. Whereas the females inherit both alleles, one from the mother and one from the father. In all cases the father passed down the recessive allele (Xr) and the mother passed down the dominant (XR) and recessive (Xr). 50% of the females are all carriers and their eye colour shows up as red, due to the mother passing down her (XR) allele and the father passing down his (Xr) allele. The rest of the females have white eyes due to the father passing down his (Xr) allele and the mother passing down her (Xr) allele.

1. Knowing that Nancy has a family history in Huntington disease and she is heterozygous for the disease (Hh), it is likely that she will progress the disease later on in life. This is due to Huntington disease being inherited in a dominant pattern; this means even if an individual possesses one copy of the Huntington disease allele, it is sufficient to lead to this disorder. The major symptoms, such as poor coordination and involuntary movements, of this progressive brain disorder usually appear at the ages thirty to forty. It disables the individual to control their movements, also emotional problems will arise and the ability to think will be blocked. It is known that Simon has been diagnosed as being colour blind and Nancy being a carrier. Due to the fact that colour blindness is a recessive disorder which is passed down by the X chromosome, it could be said that the mothers’ sex chromosomes determine the male offspring’s possibility of being colour blind. Colour blindness’ most common form is named the red/green colour blindness. Red/green colour blindness sufferers mix up all the colours that have some red and/or green as part of the entire colour. For example they will see pink as white as they view red colour component is separated from the pink. According to the punnet square results only 25% of the offspring’s will have neither of the disorders and 75% will have at least one of them. Therefore, if the couple want to have a child of their own it is a risk worth taking. Their other option is to have In Vitro Fertilisation (IVF) treatment done as this allows the egg and the sperm to be fertilised outside the body, this way the traits that are being passed down could be tracked and determined to give birth to a healthy child.