In an inheritance case, a man has died leaving his estate to be divided equally between 'his wife and his offspring.' His wife (M) has an adult daughter (D), and they argue that they should split the estate equally. As a young couple, however, the man and his wife had a son that they gave up for adoption. Two men have appeared, each claiming to be the son of the couple and therefore entitled to a one-third share of the estate. The accompanying illustration shows the results of DNA analysis for five genes for the mother (M), her daughter (D), and the two claimants (S1 and S2). Do the DNA results suggest that either man is likely to be the son of the man and his wife? Explain.

Verified step by step guidance

1. Step 1: Understand the genetic inheritance pattern for autosomal genes. Each child inherits one allele from the mother and one allele from the father at each gene locus. Therefore, for each gene tested, the child must have one allele that matches the mother's alleles and one allele that matches the father's alleles.
2. Step 2: Examine the DNA profiles of the mother (M), daughter (D), and the two claimants (S1 and S2) for each of the five genes. For each gene, identify the alleles present in the mother and check if each claimant has at least one allele matching the mother’s alleles, as this is necessary for a biological child.
3. Step 3: For each gene, check if the claimants have alleles that could have come from the father. Since the father's genotype is unknown, any allele in the claimant that is not present in the mother could potentially be inherited from the father. However, if a claimant has alleles that are not present in either the mother or the daughter (who shares the mother’s alleles), this could indicate a mismatch.
4. Step 4: Look for inconsistencies or mismatches in the claimants’ alleles compared to the mother’s alleles across all five genes. A true biological child should not have alleles that are impossible to inherit from the mother. Multiple mismatches across several genes reduce the likelihood that the claimant is the biological son.
5. Step 5: Summarize the findings by comparing the number of matching alleles for each claimant with the mother’s alleles. If one claimant consistently shares alleles with the mother at all loci, this supports the claim of biological parentage. If the other claimant shows multiple mismatches, it suggests he is unlikely to be the biological son.

Key Concepts

Mendelian Inheritance and Genetic Markers

Mendelian inheritance explains how genes are passed from parents to offspring, with each child inheriting one allele from each parent. Genetic markers, such as specific gene loci, can be analyzed to determine biological relationships by comparing alleles. Matching alleles between a child and a parent at multiple loci increases the likelihood of biological relatedness.

DNA Profiling and Paternity Testing

DNA profiling uses genetic markers to establish biological relationships by comparing DNA sequences. In paternity testing, the child's DNA is compared to the alleged parent's DNA at multiple loci; a high number of matching alleles supports paternity, while mismatches reduce the probability. This method is highly reliable for confirming or excluding biological parentage.

Interpretation of Genetic Evidence in Legal Contexts

Genetic evidence must be interpreted carefully in legal cases involving inheritance claims. The presence or absence of matching alleles at multiple gene loci can confirm or exclude biological relationships, impacting estate division. Understanding the statistical likelihood and limitations of DNA evidence is crucial for fair legal decisions.