BIOLOGY 2C03 Lecture 4: Lecture 4 - February 4, 2013.docx
Document Summary
Continuous variation an assume any value between two values (boundaries); the number of phenotypes is limited by the resolution of the measurement tool: eg/ human height, seed weight, milk production. Threshold characteristics not continuous, trait is simply present or absent, but determined by multiple factors: eg/ human cancer present or absent but many contributing factors. Polygenic inheritance in wheat (nilsson-ehle did the same sort of study as mendel; parental cross between two pure breeding lines) Modified dihybrid ratio: assign genes as if it were a dihybrid cross, assign alleles as contributing or noncontributing (like incomplete dominance at each gene) The difference between qualitative and quantitative characteristics is the number of loci influencing the trait. How many genes are contributing: monohybrid: resemble a true-breeding parent, dihybrid: 1/16 resemble a true-breeding parent, trihybrid: 1/64 resemble a true-breeding parent. General rule: (!/4)n of the f2 are similar to one of the original parents n = the number of participating genes.
