Task: human dysplasia is transferred as recessive attribute linked with x chromosome
a) a man without this disorder marries a women whose father had this disorder but mother had healthy pedigree. what are the chances that new offspring will have this disorder?
b) a healthy women marries a man with this disorder, a sick girl and healthy son are born. what are the chances of another offspring born without disorder?
а) man is healthy (disorder is recessive X-linked), so his genotype is XY
woman is healthy too (but she has two copies of X-chromosome and can be a carrier)
her mother and all her pedigree had a XX, XY healthy genotype, but her father had this disorder (genotype: XdisorderY) and give this disorder to his daughter, so she is a carrier of this disorder (genotype Xdis. X)
genotypes of parents: XY * Xdis. X (if girl - she will be healthy, if boy - 50% of transferring mother allele with disorder)
So, 1/2 (probability that boy will born) * 1/2 (probability of transferring the disorder) = 1/4 or 25%
b) the genotype of man is Xdis. Y, the genotype of woman depends from the offspring
Sick girl can be born if only mother and father both transferred X chromosome with disorder
genotype of woman Xdis. X (because of healthy boy - at least one normal allele)
So, there is a 50% of boys born with this disorder, and 50% of girls born with this disorder
In summary, 50% of all offspring in this family can have this disorder, and respectively 50% of all offspring will not have this disorder.