Lecture 3: Gene Segregation and Interaction

• Law of Independent Segregation - alleles of gene pair separate completely and cleanly from each other during meiosis.
• Law of Independent Assortment - alleles of different gene pairs separate completely and cleanly from each other and randomly combine during meiosis.
• Allele interactions - only one gene controls a trait.
• Complete dominance - heterozygotes are phenotypically identical to homozygous dominants.
• Overdominance - heterozygotes exhibit a superior phenotype compared to either homozygous.
• Incomplete Dominance - heterozygotes are phenotypically intermediate between two homozygous types.
• Codominance - Heterozygotes exhibit a mixture of the phenotypic characteristics of both homozygotes instead of single intermediate expression.
• Dominant Lethal - Death of affected indiv. (homo dominant or hetero) occurs after reproduction ahs taken place.
• Recessive Lethal - Effects of recessive genes are sufficiently drastic to kill the bearers of the certain genotypes.
• Non-allelic interactions - two genes are controlling one trait.
• Epistasis - an allele of a gene masks the effect of the allele of the other gene.
• Dominant Epistasis

  • complete dominance at both gene pairs but one gene when dominant is epistatic to the other.
  • complete dominance at both gene pairs. one gene when dominant is epistatic to the other, while the other when homo recessive is epistatic to the homozygous recessive state of the first gene.
• Recessive Epistasis - complete dominance at both gene pairs, but one gene when homo recessive is epistatic or masks the effect of other gene.
• Duplicate Genes - complete dominance at both gene pairs, but either gene, when dominant is epistatic to the recessive of other.
• Complementary Genes - complete dominance at both gene pairs, but either gene when homo recessive is epistatic to the effects of the dominant allele of the other gene.
• Novel Phenotypes - complete dominance at both gene pairs. New phenotypes are produced from the interaction between dominants , and between homozygous recessives.
• Novel phenotypes - 9:3:3:1
• Complementary Genes - 9:7
• Duplicate Genes - 15:1
• Recessive Epistasis - 9:3:4
• Dominant Epistasis - 12:3:1 and 13:3
• Recessive Lethal - 1:2, 3:0, and 1:2
• Dominant Lethal - 0:1
• Codominance, Incomplete, and Overdominance - 1:2:1
• Complete Dominance - 3:!