Non-Mendelian Traits

Overview

• Non-Mendelian traits do not follow the classic Mendelian inheritance patterns.
• Examples include snapdragons, human height, and speckled chickens.
• These traits show that having a dominant allele does not always mean the dominant trait will show.

Incomplete Dominance

• Definition: The dominant allele is not completely expressed when the recessive allele is present.
• Example: Snapdragons
  • Phenotypes: Red, White, Pink (in-between)
  • Cross a red flower (RR) with a white flower (rr): Offspring are pink (Rr).
  • Crossing pink flowers (Rr) can result in red, white, or pink offspring.

Co-Dominance

• Definition: Both alleles are expressed together, like co-workers.
• Example: Color in some chickens
  • Cross a black chicken (BB) with a white chicken (WW): Offspring are speckled (BW), showing both black and white traits.
• Different formatting may be used for expressing these alleles.

Polygenic Traits

• Definition: Traits controlled by many genes.
• Examples: Human height and skin color
  • No single pair of alleles determines these traits.
  • Environmental factors (e.g., nutrition, sun exposure) can also influence the expression of these traits but do not change the genetics.

Epistasis

• Definition: One gene's expression depends on another gene.
• Example: Llama wool color
  • Black wool: Big B allele.
  • Brown wool: Little b allele.
  • Another gene (C) controls if wool color is expressed.
    • Genotype cc prevents expression of wool color genes, resulting in an albino llama.

Conclusion

• Many other non-Mendelian traits exist, such as traits influenced by multiple alleles and sex-linked traits.
• It's important not to assume non-Mendelian inheritance in genetic problems unless clues are provided.

Reminder

• Stay curious and continue exploring genetic traits beyond the Mendelian framework.