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.
Draw a pedigree of this family, including the woman, the man, their siblings, parents, and grandparents.

Verified step by step guidance

1. Identify all individuals to be included in the pedigree: the woman, the man, their siblings, parents, and grandparents. This will form three generations for each side of the family.
2. Assign genotypes based on the information given: the woman is homozygous dominant (GG), her father, sister, and paternal grandmother are heterozygous carriers (Gg), and her paternal grandfather, mother, and maternal grandparents are homozygous dominant (GG). The man is heterozygous (Gg), and his brother has Gaucher disease (gg). The man's parents and grandparents are not tested but are unaffected, so they are likely either GG or Gg but not gg.
3. Start drawing the pedigree by placing the grandparents at the top level, then the parents in the middle, and the siblings at the bottom. Use standard pedigree symbols: squares for males, circles for females, shaded symbols for affected individuals (gg), half-shaded or dots for carriers (Gg), and unshaded for homozygous dominant (GG).
4. Connect individuals with lines to represent mating pairs and vertical lines to their offspring. Label each individual with their genotype where known, and indicate carriers and affected individuals clearly.
5. Review the pedigree to ensure all relationships and genotypes are correctly represented, reflecting the inheritance pattern of Gaucher disease (an autosomal recessive disorder) and the information provided.

Key Concepts

Mendelian Inheritance and Allele Notation

Mendelian inheritance explains how alleles are passed from parents to offspring, with dominant alleles masking recessive ones. In this question, 'G' is the dominant allele and 'g' is the mutant recessive allele causing Gaucher disease. Understanding homozygous (GG or gg) and heterozygous (Gg) genotypes is essential for predicting phenotypes and constructing pedigrees.

Autosomal Recessive Inheritance Pattern

Gaucher disease is inherited in an autosomal recessive manner, meaning an individual must inherit two copies of the mutant allele (gg) to express the disease. Carriers (Gg) are typically asymptomatic. Recognizing this pattern helps interpret family genotypes and phenotypes, especially when some relatives are carriers and others are affected.

Pedigree Construction and Interpretation

A pedigree is a diagram that shows family relationships and the inheritance of traits across generations. It uses standardized symbols to represent individuals and their genotypes or phenotypes. Drawing the pedigree based on the given genotypes and phenotypes helps visualize inheritance patterns and identify carriers, affected individuals, and unaffected family members.