The accompanying pedigree below shows a family in which an autosomal recessive disorder is present. Family members I-2 and II-2 are affected by the disorder and have the genotype dd. A pregnancy involving II-4 has just undergone genetic testing for a VNTR that is linked to the disease gene. The VNTR has a recombination frequency of r = 20 with the disease gene. The VNTR has two alleles, V₁ and V₂. The gel electrophoresis patterns for each family member are shown, including the VNTR genotype for II-4. Based on the information given, answer the following questions about the family. Excluding II-4, what is the genotype of each family member for the disease gene?

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait or disorder is expressed only when an individual has two copies of the recessive allele (e.g., dd). Carriers, who possess one dominant and one recessive allele (Dd), do not exhibit the disorder but can pass the recessive allele to their offspring. In a pedigree, affected individuals typically have unaffected parents, highlighting the need for both parents to contribute a recessive allele for the disorder to manifest.

VNTR (Variable Number Tandem Repeat)

VNTRs are repetitive sequences in the DNA that vary in length between individuals. They can be used as genetic markers in linkage analysis, helping to identify the inheritance patterns of genes associated with specific traits or disorders. In this context, the VNTR's recombination frequency indicates its proximity to the disease gene, which is crucial for determining the genotypes of family members based on their gel electrophoresis patterns.

Gel Electrophoresis

Gel electrophoresis is a laboratory technique used to separate DNA fragments based on their size and charge. In the context of genetic testing, it allows visualization of different alleles present in individuals by producing distinct banding patterns. By comparing these patterns, one can infer the genotypes of family members for specific genetic markers, such as the VNTR linked to the autosomal recessive disorder in the pedigree.