(amoeba sisters video recap: pedigrees and need

16. A Couple with the ability to taste PTC have two grown sons and one grown daughter. The sons have the ability to taste PTC. Their daughter is a PTC non-taster. She married with a PTC non-taster man and have two sons.

The ability to taste Phenylthiocarbamide or PTC is inherited by autosomal dominant trait. The daughter of the first generation should be autosomal recessive(tt) as she was a non-taster. That means her parent would be heterozygotes(Tt) since they have the ability to taste PTC. Her brother could be homozygote dominant(TT) or heterozygote(Tt). The pedigree would be:
i. no-shade square(Tt) -----------------no-shade circle(Tt)
ii. no-shade square(T?), no-shade square(T?), shaded circle(tt)------shaded square(tt)
iii. shaded square(tt) and shade square(tt), 

17. She marries with non-taster too which means also a homozygote recessive. Since both parents are homozygote recessive, the children should be 100% homozygote recessive too.
The phenotype of the sons in generation III would be 100% non-taster.

18. The genotype of the female should be XX. To express the recessive trait, an individual need to have all recessive genes. If she has a recessive trait of an X-linked disease then both of the X genes should have a lowercase letter(recessive).

C.

19. The genotype of a male should be XY. If he has a recessive trait of an X-linked disease then the X genes should have a lowercase letter(recessive). As there is only one X gene in male, to express recessive he only needs 1 recessive gene.
 
E. Y