Question

The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated hereby the colored circles and squares, are unable to metabolize a substance called alkapton, which colors the urine and stains body tissues. Does alkaptonuria appear to be caused by a dominant allele or a recessive allele? Fill in the genotypes of the individuals whose genotypes can be deduced. What genotypes are possible for each of the other individuals?

Short answer

A recessive allele causes alkaptonuria because the offspring of two normal individuals are affected.

The possible genotypes of other individuals are as follows:

George:Aa

Sandra:AA orAa

Sam:Aa

Ann:Aa

Micheal:Aa

Daniel:Aa

Alan:Aa

Tina: AA orAa

Christopher: AA or Aa

Step-by-step solution

Pedigree

When a chart represents the inheritance of a trait to show the affected and normal individuals of the family and their relationships, then such chart is called a pedigree.

In pedigree, females are represented by a circle and males by squares. A colored circle or square represents an affected female or male, respectively.

Inheritance of alkaptonuria

In the pedigree pattern, Ann and Micheal are not affected, but their daughter Caria is affected. This means a recessive allele causes alkaptonuria. However, in the case of a dominant trait, at least one parent possesses the trait.

In X-linked traits, males are more affected in females, but females are more affected in this pedigree than males. This exhibits that alkaptonuria cannot be a sex-linked trait; instead, it is an autosomal trait.

Thus, alkaptonuria is an autosomal-recessive trait.

Genotype of the affected individuals

Assume A is the dominant allele and a is the recessive allele for the gene, causing alkaptonuria. Then, the genotype of the homozygous individual would be AA, and that of heterozygous would be Aa.

From the pedigree, it can be inferred that four individuals, Ariene, Tom, Wilma, and Caria, are affected. This means these individuals possess both the recessive alleles as they are affected. Thus, the genotype of Ariene, Tom, Wilma, and Caria would be aa.

Genotype of other individuals in the pedigree

The genotype of other individuals in the pedigree can be determined through their relationship with their families. Thus, genotypes are as follows:

George: George must be heterozygous because he has an affected son and daughter. Thus, the genotype of George would be Aa.

Sandra: Sandra can either be homozygous or heterozygous for the trait because she comes from another family. Thus, the genotype of Sandra would be AAorAa.

Sam: Sam would be heterozygous because he has a carrier father (George) and an affected mother (Ariene). Thus, the genotype of Sam would be Aa.

Ann: Sam would be heterozygous because she has a carrier father (George) and an affected mother (Ariene). Thus, the genotype of Ann would be Aa.

Micheal: Micheal must be heterozygous for the trait because he has an affected daughter (Caria) with a carrier wife (Ann). Thus, the genotype of Micheal would be Aa.

Daniel: Daniel would be heterozygous for the trait because he has an affected father (Tom). Thus, the genotype of Daniel would be Aa.

Alan: Alan would be heterozygous for the trait because he has an affected father (Tom). Thus, the genotype of Alan would be Aa.

Tina: Tina can either be heterozygous or homozygous for the trait because she comes from another family. Thus, the genotype of Tina would be AA or Aa.

Christopher: Christopher can either be heterozygous or homozygous for the trait because none of his parents is affected. Thus, the genotype of Christopher would be AA or Aa.

Thus, the genotype of individuals of a family can be determined through the pedigree chart.