Question

A couple and some of their relatives are screened for Gaucher disease in a community-based screening program. The woman is homozygous for the dominant allele, represented by G. The woman's father, sister, and paternal grandmother are heterozygous carriers of the mutant allele, represented by g. Her paternal grandfather, her mother, and both of her mother's parents are homozygous for the dominant allele. The man is heterozygous and he has a brother with Gaucher disease. The man's parents and grandparents have not been tested, but it is known that none of them has Gaucher disease.
On the pedigree, write the genotypes (GG, Gg, or gg) for each person who has been tested or for whom you can deduce a genotype. If a genotype cannot be determined completely, list the alleles you know or deduce must be present.

Accepted Answer

Identify the alleles involved: G is the dominant normal allele, and g is the recessive mutant allele causing Gaucher disease. Individuals with genotype gg have the disease, Gg are carriers, and GG are unaffected non-carriers. Start with the woman: she is homozygous dominant (GG), so both her alleles are G. This means she inherited one G allele from each parent. Analyze the woman's family: her father, sister, and paternal grandmother are heterozygous carriers (Gg), so each has one G and one g allele. Her paternal grandfather, mother, and maternal grandparents are homozygous dominant (GG). Use this information to assign genotypes to these individuals. Consider the man: he is heterozygous (Gg), so he carries one G and one g allele. Since he has a brother with Gaucher disease (gg), both parents must carry at least one g allele, even though they are not tested and do not have the disease themselves (implying they are likely Gg). For any individuals without direct test results, use Mendelian inheritance rules and the known genotypes of their relatives to deduce possible genotypes or at least the alleles they must carry. If a genotype cannot be fully determined, list the alleles that must be present based on inheritance.

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Concetti chiave

Mendelian Inheritance and Allele Dominance

Carrier Status and Genotype Deduction

Pedigree Analysis and Genotype Assignment