Nail–patella syndrome is an autosomal disorder affecting the shape of nails on fingers and toes as well as the structure of kneecaps. The pedigree below shows the transmission of nail–patella syndrome in a family along with ABO blood type.

Explain why III-6 has nail–patella syndrome and III-8 does not. Give genotypes for these two individuals.

Verified step by step guidance

1. Step 1: Understand the inheritance pattern of nail–patella syndrome. Nail–patella syndrome is an autosomal dominant disorder, meaning that only one copy of the dominant allele is required for an individual to express the trait. If a parent has the disorder, there is a 50% chance of passing it to their offspring.
2. Step 2: Analyze the pedigree provided. Look at the family tree to determine which individuals have nail–patella syndrome and which do not. Identify the inheritance pattern and note whether III-6 and III-8 inherited the dominant allele associated with the disorder.
3. Step 3: Determine the genotype for nail–patella syndrome. Since it is autosomal dominant, individuals with the disorder will have at least one dominant allele (e.g., 'N'). Those without the disorder will have two recessive alleles (e.g., 'nn'). Assign genotypes based on the presence or absence of the syndrome.
4. Step 4: Consider the ABO blood type information. ABO blood type is inherited independently of nail–patella syndrome, but it can provide additional clues about the genotypes of III-6 and III-8. Use the blood type information to refine the genetic analysis if necessary.
5. Step 5: Combine the information. Based on the pedigree and the inheritance patterns, explain why III-6 has nail–patella syndrome (likely inherited the dominant allele 'N') and III-8 does not (likely inherited two recessive alleles 'nn'). Provide the genotypes for both individuals, including their nail–patella syndrome alleles and ABO blood type alleles.

Key Concepts

Autosomal Dominant Inheritance

Nail-patella syndrome is inherited in an autosomal dominant manner, meaning that only one copy of the mutated gene from an affected parent can cause the disorder. This type of inheritance typically results in the condition appearing in every generation, as affected individuals have a 50% chance of passing the trait to their offspring.

Genotype and Phenotype

The genotype refers to the genetic makeup of an individual, while the phenotype is the observable expression of that genotype. In the case of nail-patella syndrome, an individual with the genotype 'Nn' (where 'N' is the normal allele and 'n' is the mutated allele) will express the syndrome, whereas an individual with the genotype 'NN' will not.

Pedigree Analysis

Pedigree analysis is a diagrammatic method used to trace the inheritance of traits through generations in a family. By examining the pedigree provided, one can determine the genotypes of individuals based on their phenotypes and the patterns of inheritance, helping to explain why certain family members exhibit or do not exhibit the syndrome.