Non Mendelian Genetics

 Genetics and Inheritance Patterns

1. Dihybrid Cross Example: Red and Thorny Roses

• Traits:
  • R (Red) is dominant to r (White).
  • T (Thorny) is dominant to t (Not thorny).
• Cross:
  • Parent 1: RRTt (Homozygous Red, Heterozygous Thorny).
  • Parent 2: RrTt (Heterozygous Red and Thorny).
• Punnett Square:
• Generates phenotypes in a 3:1 ratio (Red thorny : Red not thorny).

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2. Orange and Black Striped Tigers

• Traits:
  • R (Orange coat) is dominant to r (White coat).
  • B (Dark black stripes) is dominant to b (Muted stripes).
• Cross:
  • Parent 1: RrBb (Orange coat, Dark stripes).
  • Parent 2: rrbb (White coat, Muted stripes).
• Phenotypic Ratios:
• 1:1:1:1 ratio:
• Orange Black.
• Orange Muted.
• White Black.
• White Muted.

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Non-Mendelian Genetics

1. Incomplete Dominance

• Definition:
  • A blending of traits occurs in heterozygous individuals.
  • Example:
    • RR = Red flowers.
    • rr = White flowers.
    • Rr = Pink flowers.
• Phenotype Ratio: 100% Pink (when crossing two heterozygous individuals).

2. Codominance

• Definition:
  • Both alleles are fully expressed in the phenotype of heterozygous individuals.
  • Example: Blood Types
    • IA IA = Type A.
    • IA IB = Type AB (both A and B fully expressed).
    • ii = Type O.
• Punnett Square: Crossing IA IB x IA IB generates:
• Phenotypic ratio: 1 A : 2 AB : 1 B.

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3. Sex-Linked Traits (X-Linked Recessive)

• Example: Hemophilia
  • H = Healthy.
  • h = Hemophilia.
  • Males (XY) are more likely to express the trait since they have only one X chromosome.
  • Females (XX) can be carriers (heterozygous) or express the trait if homozygous recessive.
• Punnett Square:
• Carrier mother (XH Xh) and healthy father (XH Y) produce:
• Phenotypic Ratios:
• 1 Female Healthy Carrier.
• 1 Female Healthy.
• 1 Male Hemophiliac.
• 1 Male Healthy.