MIDTERM 1 : BIOL 234 ,ANSWERS

1. (10 marks) In corn Zea mays, Les (“lesion”) mutants have patches of dead cells all over the leaves, and wild-type levels of sugar in the corn kernels. Sug mutants with the “sugary” phenotype make extra sweet corn kernels, and have wild-type leaves (no patches of dead cells). A pure-breeding Les strain was mated with a pure-breeding Sug strain. The F1 corn from this cross all had lesions with normal sweetnes levels in the kernels. These Les F1 plantss were allowed to self, and 2000 F2 plants were scored, revealing 4 distinct phenotypic classes: wild-type (no lesions and normal sugar), Sug (no lesions, with extra sweetness), Les (lesions with normal sugar) and Les Sug (lesions with extra sweetness). F2 phenotype Numbers observed Wild-type 378 Les 1125 Sug 125 Les Sug 372 a. List what you can conclude based on this F1 data alone Lesions are dominant to wild-type leaves Normal sweetness is dominant to sweet corn kernels F1s are dihybrid.(could say learned F1s are dihybrid by looking at F2) b. Provide a complete genetic explanation for the above F2 data. Your explanation should include the genotypes of the original pure-breeding parents, the F1 plants, and the F2 offspring listed in the table above. Define all genes and alleles, and allelic relationships. Show all of your work. 1. A cross was made between two strains of plants that are agriculturally important. One strain was disease resistant but herbicide sensitive; the other strain was disease sensitive but herbicide resistant. A plant breeder crossed these purebreeding plants and allowed the F1 generation to self-fertilize and produce an F2 generation. The following results were obtained: F1 generation: all offspring are disease sensitive and herbicide resistant F2 generation: 229 disease sensitive and herbicide resistant 72 disease sensitive and herbicide sensitive 78 disease resistant and herbicide resistant 21 disease resistant and herbicide sensitive total 400 a. List what you can conclude based on this F1 data alone.