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.

Using N and n to represent alleles at the nail–patella locus and Iᴬ, Iᴮ and i to represent ABO alleles, write the genotypes of I-1 and I-2 as well as their five children in generation II.

Key Concepts

Autosomal Inheritance

Autosomal inheritance refers to the transmission of genetic traits that are located on the autosomes, which are the non-sex chromosomes. In the case of nail-patella syndrome, it is inherited in an autosomal dominant manner, meaning that only one copy of the mutated allele (N) is sufficient to express the disorder. Understanding this concept is crucial for determining the genotypes of affected individuals in the pedigree.

Genotype and Phenotype

The genotype is the genetic constitution of an individual, represented by the alleles they possess, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. In this question, identifying the genotypes of individuals I-1 and I-2 will help predict the phenotypes of their children, as the combination of alleles they pass on will determine the traits expressed in the next generation.

ABO Blood Type System

The ABO blood type system is determined by the presence of specific antigens on the surface of red blood cells, which are encoded by three alleles: Iᴬ, Iᴮ, and i. The inheritance of these alleles follows Mendelian principles, and understanding how these alleles interact is essential for determining the blood types of the individuals in the pedigree. This knowledge is important for accurately writing the genotypes of I-1, I-2, and their children.