Question

A woman has a rare eyelid abnormality called ptosis, which makes it impossible for her to open her eyes all the way. The condition is caused by a dominant allele. The woman's father had ptosis but her mother was normal. Her father's mother also had normal eyelids.a. What are the genotypes of the woman, her father, and her mother? b. What proportion of the woman's children will have ptosis if she marries a man with normal eyelids?

Answer 1

If you keep in mind that a child gets one gene from the father, andanother from the mother, all should be fine.

a) starting with the father: since he is infected, he then has atleast one P. Knowing his mother wasn't, then her genotype was pp.Since he must have gotten one of her genes, then the father'sgenotype is Pp.
Since her mother had normal eyes, she must have had pp, because ifshe had even one P, she would have ptosis -since the allele isdominant-.
Since the woman is infected, and her mother is pp, then for thesame reasoning as her father, her genotype is Pp.

b) so this is a cross between Pp X pp. Draw your punnets square.There's a 50% chance that her children will have pp genotype thusno ptosis. 50% of her children will have ptosis with genotype Pp.