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.
Table of contents
- 1. Introduction to Genetics51m
- 2. Mendel's Laws of Inheritance3h 37m
- 3. Extensions to Mendelian Inheritance2h 41m
- 4. Genetic Mapping and Linkage2h 28m
- 5. Genetics of Bacteria and Viruses1h 21m
- 6. Chromosomal Variation1h 48m
- 7. DNA and Chromosome Structure56m
- 8. DNA Replication1h 10m
- 9. Mitosis and Meiosis1h 34m
- 10. Transcription1h 0m
- 11. Translation58m
- 12. Gene Regulation in Prokaryotes1h 19m
- 13. Gene Regulation in Eukaryotes44m
- 14. Genetic Control of Development44m
- 15. Genomes and Genomics1h 50m
- 16. Transposable Elements47m
- 17. Mutation, Repair, and Recombination1h 6m
- 18. Molecular Genetic Tools19m
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
18. Molecular Genetic Tools
Methods for Analyzing DNA
Problem E.12a
Textbook Question
Three independently assorting STR markers (A, B, and C) are used to assess the paternity of a colt recently born to a quarter horse mare. Blood samples are drawn from the mare, her colt, and three possible male sires (S₁, S₂, and S₃). DNA at each marker locus is amplified by PCR, and a DNA electrophoresis gel is run for each marker. Amplified DNA bands are visualized in each gel by ethidium bromide staining. Gel results are shown below for each marker. Evaluate the data and determine if any of the potential sires can be excluded. Explain the basis of exclusion, if any, in each case.

1
Step 1: Understand the principle of paternity testing using STR markers. Each individual inherits one allele from the mother and one allele from the father at each STR locus. Therefore, the colt's alleles at each marker must be a combination of one allele from the mare and one allele from the sire.
Step 2: For each STR marker (A, B, and C), compare the alleles present in the colt with those of the mare. Identify which allele in the colt must have come from the sire by excluding the allele inherited from the mare.
Step 3: For each potential sire (S₁, S₂, and S₃), check if they possess the allele(s) that the colt must have inherited from the father at each marker. If a potential sire lacks the required allele at any marker, that sire can be excluded as the biological father.
Step 4: Repeat this comparison for all three markers independently, since the markers assort independently. A sire must have matching alleles at all markers to be considered a possible father.
Step 5: Summarize the results by listing which sires can be excluded based on the absence of required alleles at one or more markers, and explain that exclusion is based on Mendelian inheritance patterns where the colt must inherit one allele from each parent at every locus.

This video solution was recommended by our tutors as helpful for the problem above
Video duration:
2mPlay a video:
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Independent Assortment of STR Markers
Short Tandem Repeat (STR) markers are specific DNA sequences used in genetic profiling. When markers assort independently, the inheritance of one marker does not affect the others, allowing each locus to be analyzed separately. This principle helps in paternity testing by comparing alleles at multiple loci to increase accuracy.
Recommended video:
Guided course
Gamete Genetics and Independent Assortment
Paternity Exclusion Principle
Paternity exclusion occurs when an alleged sire lacks one or more alleles present in the offspring that must have been inherited from the father. If the sire’s genotype does not share at least one allele at each marker locus with the offspring, he can be excluded as the biological father.
Recommended video:
Guided course
X-Inactivation
PCR Amplification and Gel Electrophoresis in DNA Analysis
Polymerase Chain Reaction (PCR) amplifies specific DNA regions, such as STR loci, to detectable levels. Gel electrophoresis separates these amplified fragments by size, visualized by ethidium bromide staining. The resulting band patterns represent alleles, which are compared across individuals for genetic relationship analysis.
Recommended video:
Guided course
Step 2
Watch next
Master Methods for Analyzing DNA and RNA with a bite sized video explanation from Kylia
Start learningRelated Videos
Related Practice
Textbook Question
351
views