A family consisting of a mother (I-1), a father (I-2), and three children (II-1, II-2, and II-3) are genotyped by PCR for a region of an autosome containing repeats of a 10-bp sequence. The mother carries 16 repeats on one chromosome and 21 on the homologous chromosome. The father carries repeat numbers of 18 and 26.

Identify all the possible genotypes of children of this couple by specifying PCR fragment lengths in each genotype.

Key Concepts

Genotype and Alleles

A genotype refers to the genetic constitution of an individual, specifically the alleles present at a given locus. In this case, the mother has two different alleles for the repeat sequence (16 and 21), while the father has alleles of 18 and 26. The combination of these alleles from both parents will determine the genotypes of their children.

PCR and Fragment Lengths

Polymerase Chain Reaction (PCR) is a technique used to amplify specific DNA sequences, allowing for the analysis of genetic material. The length of the PCR fragments produced is directly related to the number of repeats in the sequence. For example, a 10-bp repeat will result in fragment lengths that can be calculated based on the number of repeats present in the genotype.

Inheritance Patterns

Inheritance patterns describe how genetic traits are passed from parents to offspring. In this scenario, the children can inherit one allele from each parent, leading to various combinations of the repeat numbers. The possible genotypes for the children can be determined by combining the alleles from both parents, resulting in different fragment lengths based on the inherited alleles.