Lecture 4 April 12, 2012 “Extensions on Mendel Continued” Pedigree of ABO Blood Conclusions - When heterozygous offspring look like one parent but not the other - complete dominance, dominance series. - When heterozygotes show a phenotype unlike that of either parent - incomplete dominance. o New Phenotype “Pink” - When heterozygotes show characteristics of both parents - co-dominance. o Reflect both Parent Allele- Genes interact with the environment; phenotypic differences between genotypes can vary with external conditions. Allelic Series: Determining the order of Dominance - How can you determine how multiple alleles of a single gene interact with one another? - The functional relationships among the members of a series of multiple alleles can be studied by making heterozygous combinations through crosses between homozygotes. -The heterozygotes allow the dominance relations among the alleles to be studied.Pleiotropy- One Gene Determine Multiple Trait - Most of our genetic examples have been cases in which each gene specified only one hereditary characteristic. - Pleiotropy: the impact of a single gene on more than one hereditary characteristic Pleiotropy and Sickle-Cell Disease - Most of our genetic examples have been cases in which each gene specified only one hereditary characteristic. - Pleiotropy: the impact of a single gene on more than one hereditary characteristicEpistasis- When two or more genes influence a trait, an allele of one of them may have an overriding effect on the phenotype. - Over powers the other allele. two common ratio 12:3:1 9:3:4 - When an allele of one gene has such an overriding effect, it is said to be epistatic to the other gene.- Molecular Explanation: Both genes are needed to make one final product…Anthocyanin -Each dominant allele (C, P) produces an enzyme that controls a step in the synthesis of anthocyanin from a biochemical precursor. If a dominant allele is not present, its step in the biosynthetic pathway is blocked and anthocyanin is not