What is a leaky recessive allele? What is the phenotype of a homozygote for a le

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mutation /mu·ta·tion/ (mu-ta´shun) a permanent transmissible change in the genetic material. Also, an individual exhibiting such change; a sport. point mutation a mutation resulting from a change in a single base pair in the DNA molecule. somatic mutation a genetic mutation occurring in a somatic cell, providing the basis for a mosaic condition. suppressor mutation a mutation that partially or completely masks phenotypic expression of a mutation but occurs at a different site from it (i.e., causes suppression); it may be intragenic or intergenic. It is used particularly to describe a secondary mutation that suppresses a nonsense codon created by a primary mutation. 10 (4/13/04) - Dominance and Epistasis Interactions between alleles: • Complete vs. incomplete dominance eg. flower color in pea plants - wild-type purple = complete dominance white flower color (mutation in purple pigment synthesis) = fully recessive heterozygote = purple vs. flower color in petunias - wild-type red = haploinsufficient heterozygote with white allele = pink • Allelic series = "leaky" mutations (eg. missense) dominant over null alleles • Co-dominance = both alleles contribute to phenotype eg. blood groups in humans • Molecular co-dominance = detected at molecular, not phenotypic, level eg. Sickle cell anemia allele = missense mutation in hemoglobin Interactions between genes --> Modified dihybrid ratios • One trait controlled by more than one gene eg. Drosophila eye color produced by branched pathway 2 mutations disrupting both branches: 9:3:3:1 (four different eye colors) 2 mutations disrupting the same branch: 9:7 (two different eye colors) • Detectable precursor in pathway eg. mammalian coat color: colorless (white) -> brown -> black melanin 9 black:3 brown: 4 white because early mutation in pathway prevents synthesis of either pigment 9:3:4 dihybrid ratio indicates epistasis ("masking" of phenotype) • Pleiotropy = one gene controls many traits (phenotypes)

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