1	Hypothesis Testing Solving Genetics Problems Multiple Alleles Heterozygotes with a Different Phenotype Interactions among Genes
2	Reading Assignment You have already read Chapter 13. Now it is time to use your knowledge on genetics problems. On p.300 try #11, 13, 16, 19 & 21. There are also some practice problems posted in the Exam 2 section of the website.
3	Mendel’s Hypotheses One allele is DOMINANT and the other is RECESSIVE in the heterozygote. There are only two alleles at a locus. Alleles segregate in gamete formation. Loci assort independently at meiosis. Genes are not changed in heterozygotes.
4	Phenotype of Heterozygote The phenotype of a heterozygote is not always like one of the homozygotes. The heterozygote can manifest attributes of both alleles. The heterozygote can be a blend of the two homozygotes. The heterozygote can be completely different than either heterozygote, Hybrid Vigor.
5	Hybrid Vigor Hybrids between lines may be more vigorous than their inbred parents. Corn that is raised by farmers is a hybrid of a hybrid produced by seed companies. This hybrid corn has much higher yield. Hybrids in animals, such as dogs, avoid breed specific problems, but also lack breed specific desired features.
6	The ABO Blood Types
7	One RULE in doing genetics problems is that a genotype has one and only one phenotype. For each possible genotype, given the alleles you hypothesize, you must assign a single phenotype.
8	An ABO genetics problem
9	More ABO genetics A student has type A blood. Both her parents have type A blood. What observation would tell you that BOTH of her parents were heterozygous, IA i? ANSWER If any of the student’s siblings had type O blood.
10	A Drosophila Cross What do you infer from the statement that lines A and B are true-breeding lines? One line had WHITE eyes. The other had RED eyes. A male from one line was crossed to a female from the other line. The F1 had RED eyes. What genetic model would you propose that explains the available facts?
11	A Drosophila Cross The available information suggests a situation similar to that Mendel observed for seed color. Hypothesis #1: One locus, two alleles (W = Red, w = White). Red allele, W, dominant to white allele, w. PREDICTION of F2 results.
12	A Drosophila Cross Hypothesis #1 (one locus two alleles) predicts that there will be two phenotypes in the F2; RED = 0.75 WHITE = 0.25 The observed results were RED =390. WHITE = 110.
13	A Drosophila Cross Hypothesis #2. Some student noticed that there is a locus, white, on the X chromosome that results in a WHITE eye when homozygous. Both male and female F1 flies have red eyes. This is possible only if the original cross was WHITE male by RED female.
14	A Drosophila Cross Hypothesis 2 continued. The RED F1 male would produce two kinds of gametes, Y and W (or w⁺). The RED F1 females would produces two kinds of gametes, W and w, in equal proportions.
15	A Drosophila Cross
16	Comparisons of Hypotheses
17	EPISTASIS GENE INTERACTIONS There are many loci that can effect eye color in Drosophila. As is the case with the peppers described in the book (p. 291), interactions among genotypes at different loci can be complex. We will study a case of coat color in rodents.
18	A complex mouse cross
19	F2 results
20	Two loci of coat color
21	Take Home Problem In the mouse coat color problem just discussed, what proportions of BLACK, BROWN and ALBINO coats are expected in the F2 generation? What proportion of the F2 individuals are expected to be heterozygous at the albino locus?
22	Vocabulary Epistasis Hybrid vigor Rules of genetics True-breeding Quantitative prediction New phenotype Interactions among loci Sex linkage