BIOL 240 1st Edition Lecture 7Outline of Last Lecture I. Types of AllelesII. Gene NamingIII. Allele DesignationIV. Incomplete DominanceV. CodominanceVI. Multiple AllelesVII. Lethal MutationsVIII. Penetrance and ExpressivityIX. Conditional mutationsOutline of Current Lecture I. EpistasisII. Complementing GenesIII. Novel phenotypesCurrent LectureSo far we have learned that heterozygous dihybrid crosses yield 9:3:3:1 phenotypic ratios. However, this is not always the case. One reason for this is partial dominance or codominance, which we have discussed. Another is epistasis…I. Epistasis- When alleles on one locus masks the expression of the alleles at a second locus- An example of this is seen in the fur color of laborador retrievers. Labs can have one of three colors: black, chocolate, and yellow. The black and chocolate alleles are located on the same locus; black (B) is dominate to brown (b). However, the yellow allele (e) is located on a separate locus. Whenthe yellow genotype is present in the homologous form (ee), it is epistatic to the alleles at the B/b locus. Sometimes, the black and brown alleles can showslight expression around the nose and mouth of a yellow lab.- Bombay PhenotypeThese 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 This was found in a female testing for type O blood. One of her parents had type AB blood and her children received an IB allele from her. How could this be? Type O blood is homozygous, ii. Turns out, shewas found to be homozygous for a mutant allele (fut1) at the fucosyl transferase locus. This prevented her from producing the H substance,so there was no substrate to make A or B antigens. So even though she had the alleles for type A or type B blood, her blood functioned astype O.II. Complementing Genes- Yield 9:7 ratio- Mutations in different genes that give the same phenotype or result- Example: crossing parents that are homozygous for the opposite of two different genes for the same trait. AAbb yields white flowers, as well as aaBB. When crossed, the result is AaBb. A second cross will yield a 9:7 ratio where any offspring that has _ _ bb will be white, and any offspring that has aa_ _ will also be white.III. Novel phenotypes- Example of eye color in Drosophila:o wild-type eye color is brick red and depends on the interaction of other genes…o brown (bw/bw)anytime this is present, the eyes are brown.o scarlet (st/st)anytime this is present, the eyes are scarlet.o white (bw/bw;st/st)anytime both are present, the eyes are
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