Understanding Cystic Fibrosis and Family Trees

Jan 26, 2025

Family Trees and Cystic Fibrosis

Overview of Family Trees

  • Also known as family pedigrees.
  • Used to track genetic disorders, like cystic fibrosis, which is recessive.

Genetic Concepts

Cystic Fibrosis

  • Recessive Inherited Disorder
    • Requires two recessive alleles (ff) to have the disease.
    • Dominant healthy allele represented by capital F.
  • Genotypes
    • Homozygous Recessive (ff): Individual has cystic fibrosis.
    • Homozygous Dominant (FF): Individual does not have cystic fibrosis.
    • Heterozygous (Ff): Individual is a carrier, does not have the disease but can pass the allele.

Family Pedigree Symbols

  • Circles: Females.
  • Squares: Males.
  • Unshaded Shape: Person is unaffected.
  • Shaded Shape: Person has the condition.
  • Half-Shaded Shape: Person is a carrier.
  • Always use the provided key to interpret symbols.

Interpreting the Family Tree

  • Each row represents a new generation.
    • Top row: Parents
    • Second row: Children
    • Bottom row: Grandchildren
  • Horizontal lines indicate couples.
  • Unrelated individuals shown due to relationships with family members.

Example Analysis

Family Members

  • Jenny: Unaffected female (genotype FF).
  • Paul: Carrier male (genotype Ff).
  • Children:
    • Ron & Harry: Unaffected sons (genotype FF).
    • Anna & Lucy: Carrier daughters (genotype Ff).
  • Sam: Affected female (genotype ff).

Exam Application

  • Use the diagram to determine genetic probabilities.
  • Example: Probability of Lucy and Jack's baby having cystic fibrosis.
    • Both Lucy and Jack are carriers (genotype Ff).
    • Use a Punnett square:
      • 1/4 chance (25%) baby is unaffected (FF).
      • 2/4 chance (50%) baby is a carrier (Ff).
      • 1/4 chance (25%) baby has cystic fibrosis (ff).

Conclusion

  • Understanding family trees and genotypes is crucial for predicting genetic disorders like cystic fibrosis.
  • Further learning can be pursued through related videos.