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.