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-11 has nail–patella syndrome and III-12 does not. Give genotypes for these two individuals.

Verified step by step guidance

1. Step 1: Understand the inheritance pattern of nail–patella syndrome. It is described as an autosomal dominant disorder, meaning that only one copy of the dominant allele is required for an individual to express the trait. If an individual inherits the dominant allele from either parent, they will have the syndrome.
2. Step 2: Analyze the pedigree provided. Look for the transmission of the nail–patella syndrome trait across generations. Identify whether III-11 and III-12 inherited the dominant allele associated with the syndrome from their parents.
3. Step 3: Determine the genotype for nail–patella syndrome. Since it is autosomal dominant, individuals with the syndrome will have at least one dominant allele (e.g., Nn or NN), while individuals without the syndrome will have two recessive alleles (nn). Assign the appropriate genotype to III-11 and III-12 based on their phenotype (presence or absence of the syndrome).
4. Step 4: Consider the ABO blood type information provided in the pedigree. ABO blood type is inherited independently of nail–patella syndrome, but it can help confirm parental inheritance patterns. Use the blood type information to verify the genetic relationship between III-11, III-12, and their parents.
5. Step 5: Combine the information about nail–patella syndrome and ABO blood type to explain why III-11 has the syndrome (likely inherited the dominant allele) and III-12 does not (likely inherited two recessive alleles). Ensure the genotypes for both individuals are consistent with the inheritance patterns observed in the pedigree.

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 being expressed in every generation, and both males and females are equally likely to be affected. Understanding this pattern is crucial for determining the genotypes of individuals in the pedigree.

Genotype and Phenotype

The genotype refers to the genetic constitution of an individual, while the phenotype is the observable physical or biochemical characteristics. In the case of nail-patella syndrome, an individual with at least one dominant allele (N) will exhibit the syndrome, while those with two recessive alleles (nn) will not. Identifying the genotypes of III-11 and III-12 helps clarify why one has the syndrome and the other does 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 relationships between individuals and infer their genotypes based on the presence or absence of the syndrome. This analysis is essential for understanding how the trait is passed down and for predicting the likelihood of occurrence in future generations.