Overview
This lecture focuses on solving a challenging genetics exam question about blood groups and paternity testing, including how to use blood group inheritance and DNA profiling to determine potential fathers and demonstrate genetic crosses.
Blood Groups and Paternity Testing
- Blood groups are determined by alleles: Iá´¬, Iá´® (co-dominant), and i (recessive).
- Blood group O genotype is ii (two recessive alleles).
- Blood group B mother’s genotype must be Iᴮi to have a child with blood group O.
- Blood group AB individual has genotype Iá´¬Iá´® and cannot pass on the i allele.
- Blood group A can have genotypes Iá´¬Iá´¬ or Iá´¬i.
Exclusion and Confirmation using Blood Groups
- Blood group testing can only exclude potential fathers, not confirm them.
- If a child’s blood group is genetically impossible from a parent, that person is excluded as the parent.
DNA Profiling for Paternity
- In DNA profiles, the child’s unmatched DNA bands to the mother must match the biological father.
- To explain paternity: All child’s DNA bands not matching the mother match Dad 2.
Application: Exam Questions
- To exclude Dad 1: Dad 1 (AB, Iá´¬Iá´®) cannot provide the i allele needed for an O child.
- To confirm Dad 2: Dad 2 could be Iá´¬i, providing the needed i allele.
Genetic Cross (Monohybrid Cross)
- State both parents’ phenotypes (blood groups) and genotypes.
- Write out possible gametes for each parent.
- Use a Punnett square to show possible genotype combinations for offspring.
- Phenotype ratio or percentage: There is a 25% chance the child is blood group O if both parents are Iá´®i and Iá´¬i.
Key Terms & Definitions
- Allele — Different forms of a gene (e.g., Iᴬ, Iᴮ, i).
- Genotype — Genetic makeup of an organism (e.g., Iᴮi).
- Phenotype — Observable characteristic (e.g., blood group B).
- DNA Profiling — Technique to compare DNA bands between people for parentage.
- Punnett Square — Diagram to predict offspring genotypes from parental alleles.
Action Items / Next Steps
- Practice genetic crosses for blood groups using Punnett squares.
- Review how to explain exclusion/inclusion in paternity using genotype reasoning.
- Remember to include all required steps in genetic cross exam answers.