Non-Mendelian Traits

Overview

• Non-Mendelian traits are rule-breakers in genetics.
• Unlike Mendelian traits, having a dominant allele does not always mean the dominant trait will show.
• Examples include snapdragons, human height, and speckled chickens.

Incomplete Dominance

• Example: Snapdragon flowers which can be red, white, or pink.
• Characteristics:
  • There isn't a clear dominant allele.
  • The dominant allele is not fully expressed when the recessive allele is present.
  • Cross of Red (RR) and White (rr) results in Pink (Rr).
  • Cross two Pink (Rr) can result in Red, White, or Pink offspring.

Co-Dominance

• Example: Color in some types of chickens.
• Characteristics:
  • Represents alleles with different letters, e.g., Black (BB) and White (WW) chickens produce speckled chickens (BW).
  • Both traits are expressed simultaneously.

Polygenic Traits

• Traits like height and skin color are determined by many genes.
• Characteristics:
  • Multiple genes contribute to the final phenotype.
  • Example genotype for height: AABBcc, and more.
  • Can be influenced by environmental factors (e.g., nutrition, sunlight).

Epistasis

• Example: Wool color in llamas.
• Characteristics:
  • One gene affects whether another gene is expressed.
  • Example involves a gene for wool color (B) and a gene for pigment expression (C).
  • Black wool: BB or Bb, Brown wool: bb, provided the pigment gene allows expression (CC or Cc).
  • If cc is present, no pigment is expressed—resulting in albino llamas.

Additional Non-Mendelian Traits

• Includes multiple alleles and sex-linked traits.
• Non-Mendelian problems should be identified with clues or information provided.

Conclusion

• Non-Mendelian genetics offer diverse and complex patterns of inheritance beyond Mendel's rules.
• Understanding these traits requires recognizing variations in genetic expression and environmental influences.