BIOL 1411 1st Edition Lecture 17Outline of Last Lecture I. The Cell CycleII. Reproduction III. Meiosis ErrorsIV. MendelOutline of Current Lecture I. DominanceII. EpistasisLectureDominance- Mendel’s Second Law: independent assortment: alleles of different genes assort independently during gamete formationo Doesn’t often apply to different genes on the same chromosome; but different chromosomes do segregate independently- Complete dominance: heterozygotes appear similar to one of the homozygotes; used to define a dominant allele and a recessive allele- Incomplete dominance: heterozygotes have an intermediate phenotypeo Petal color alleles in snapdragonso Dihybrid crosses produce a 1:2:1 ration of phenotypes in F2o # Phenotypes= # genotypeso Also true for crosses involving co-dominant alleleso Phenotype lies between- Co-dominance= sometimes alleles at one locus produce distinct phenotypes that are both expressed in the heterozygoteo Blood types: ABO blood systemo Three common alleles: Ia, Ib, io Ia and Ib alleles are both expressed in heterozygotes. Both are completely dominant to I alleleGene interactions- Many traits are influenced by the genotype of more than a single geneo Hair color in domesticated mamals (and humans)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o Eye color in humans- Physical characteristics reflect underlying cellular functions, such as enzymatic activity within biochemical pathways- Epistasis: phenotypic expression of one gene is influenced by genotype of another geneo Ex: coat color in Labrador retrievers involves at least 2 different geneso Results in a modification of the usual 9:3:3:1 ratio of dihybrid cross 9:3:4- Mendalian traitso Single gene, affecting discreet phenotypic differences- Phenotypic variation is often complexo Phenotypes vary continuously over a range- quantitative variation Height, weight, skin pigmentation in humans Hypertension, type 2 diabetes, asthmao Phenotypic variation is usually due to the action of multiple different gene, and also influenced by the environment Individual genes can have additive effects Environment can narrow or broaden the range- Variation in human skin
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