9) Exceptions in Mendelian genetics: Allelic polymorphism, pleiotropy, epistasis, superdominance

Question 1

Allelic polymorphism

Answer 1

• Multiple alleles on the same locus
• Serial genes in order of dominance/co-dominance inheritance
• Increase combinations in populations
• Eg. colour inheritance of albino locus
• 2+ different phenotypes in the population → Diversity

Question 2

Epistasis

Answer 2

• Interlocal interaction
• One gene is dependent on another gene’s present to be expressed
• Takes place between different gene sites
• Frequently for coat colour

Question 3

Pleiotropy

Answer 3

• ‘Side effects of genes” / “Dose-effect”
• One single gene is responsible for many unrelated phenotypes
• Can be dysfunctional/lethal
• Can code for a product which is used in cells/reactions

Question 4

Superdominance

Answer 4

• Where heterozygotes (Aa) are more fit than homozygotes (AA/aa)
• Maintains polymorphisms
• Explains genetic variabilities

Question 5

X-linked inheritance

Answer 5

• Recessive x-linked alleles are expressed in the heterogametic sex
  
  • Mammals: XY (males)
  • Birds: ZW (Females)
• Example: Haemophilia