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.

Verified step by step guidance

1. Understand the problem: The question involves determining the possible genotypes of the children based on the repeat numbers of a 10-bp sequence in the parents' DNA. Each parent contributes one allele (repeat number) to the child, and the alleles are inherited independently.
2. List the alleles of the parents: The mother (I-1) has alleles with 16 and 21 repeats, while the father (I-2) has alleles with 18 and 26 repeats. These represent the possible repeat numbers that can be passed on to the children.
3. Determine all possible combinations of alleles: Each child will inherit one allele from the mother and one allele from the father. The possible combinations of alleles are: (16, 18), (16, 26), (21, 18), and (21, 26).
4. Calculate the PCR fragment lengths: Since each repeat is 10 base pairs long, the PCR fragment length for each genotype can be calculated as the sum of the repeat numbers multiplied by 10. For example, for the genotype (16, 18), the PCR fragment length is (16 × 10) + (18 × 10). Repeat this calculation for all combinations.
5. Summarize the results: The possible genotypes of the children are (16, 18), (16, 26), (21, 18), and (21, 26), with their corresponding PCR fragment lengths calculated in the previous step. These represent all the potential genotypes and fragment lengths for the children of this couple.

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 alleles with 16 and 21 repeats, while the father has alleles with 18 and 26 repeats. 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 corresponds to the number of repeats in the DNA sequence. By knowing the repeat numbers from both parents, one can predict the possible fragment lengths for the children based on the combinations of alleles inherited.

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 repeat numbers. Understanding these patterns is crucial for predicting the potential genotypes and corresponding PCR fragment lengths of the children.