Genetic Analysis Lecture Notes

Goals of Genetic Analysis

• Determine how phenotypes or traits are inherited or transmitted through generations.
• Identify if a trait is dominant, recessive, autosomal, or X-linked.

Methods of Studying Genetics

• Model Organisms:
  • Use controlled mating experiments to study inheritance patterns in lab settings.
• Human Genetics:
  • Human Pedigree Analysis:
    • Studying phenotypes of progeny retrospectively by building family trees.
    • Useful for analyzing human diseases.

Symbols in Pedigree Analysis

• Males: Squares
• Females: Circles
• Mating: Horizontal line connecting individuals
• Affected Individuals:
  • Filled squares or circles
• Unaffected Individuals:
  • Open squares or circles
• Heterozygotes for Autosomal Recessive Traits:
  • Half-filled squares or circles
• Carriers of Sex-linked Recessive Traits:
  • Circle with a dot inside (only females can be carriers)
• Deceased Individuals:
  • Diagonal slash on the square or circle

Types of Pedigree Analysis Problems

• Type 1 - Deductive Problems:
  • Inheritance pattern is known.
  • Use reasoning to determine genotypes and probabilities of traits.
• Type 2 - Inductive Problems:
  • Inheritance pattern is unknown.
  • Determine whether the trait is dominant, recessive, X-linked, or autosomal.

Example: Cystic Fibrosis Analysis

• Scenario: A normal man (whose father had cystic fibrosis) and a normal woman have a child with cystic fibrosis.
• Steps:
  1. Draw the pedigree.
  2. Determine genotypes using symbols (e.g., F1 for normal, F2 for cystic fibrosis).
  3. Use known genotypes to calculate probabilities (e.g., Punnett square or product rule).
  4. Compute probability for a second child to have cystic fibrosis (1/4).

Hallmarks of Different Inheritance Patterns

• Recessive Traits:
  • Tend to skip generations.
  • Often rare and result in sparse pedigrees.
• Dominant Traits:
  • Appear every generation.
  • More common due to higher probability of inheriting one allele.
• X-linked Recessive Traits:
  • More males affected.
  • Sons of affected mothers are always affected.
  • Unaffected daughters of affected fathers are carriers.
• Autosomal Recessive Traits:
  • Males and females equally affected.

Practice with Pedigree Analysis

• Dominant Traits:
  • Traits appearing every generation suggest dominance.
  • Consider autosomal vs. X-linked by analyzing male/female ratios.
• Recessive Traits:
  • Few affected individuals indicate recessiveness.
  • Recessive traits can manifest in offspring from unaffected parents.
  • Use genotype symbols to practice writing genotypes (e.g., Z1 for dominant, Z2 for recessive).

Conclusion

• Genetic analysis helps in understanding inheritance patterns.
• Pedigree analysis is crucial in human genetics to infer traits and genotypes.
• Practice with different types of problems strengthens understanding of genetic principles.