Given that the disease is autosomal recessive and that the parents are not affected with the disease, It must be a heterozygous cross.
Assume that this pedigree reflects the inheritance of an autosomal recessive disease allele. Use 'a' for the recessive allele and 'A' for the corresponding dominant wild type, normal allele. Neither of the two parents has the disease so they were surprised when one of their children (II-4) showed the disease symptom. Child II.5 is yet to be born, neither the sex nor the disease condition of the future child is known.
a) Assign genotypes to all individuals in the pedigree. Use A- for individuals that you know lack the disease that might be either heterozygous or homozygous dominant.
b) You know that individuals II-1, II-3, and II-4 lack the disease but that they may either be homozygotes or heterozygotes. Given just these two possibilities, what is the chance that these 3 individuals are homozygous dominant?
c) What is the chance that individuals II-1, II-3, and II-4 are heterozygous carriers?
d) For indicidual II-5, about which we know nothing, what is the chance of exhibiting the disease? Being homozygous dominant (disease allele free)? Being heterozygous carrier?