Heredity

6.a) Identify the role of treatment I in the experiment.

6.b) Provide reasoning to explain how Mutant 1 can grow on treatment I medium but cannot grow on treatment III medium.

6.c) Yeast mate by fusing two haploid cells to make a diploid cell. In a second experiment, the researcher mates the Mutant 1 and Mutant 2 haploid strains to produce diploid cells. Using the table provided, predict whether the diploid cells will grow on each of the four media. Use a plus sign (+) to indicate growth and a minus sign (−) to indicate no growth.

2.a) The double-strand breaks occur when the phosphodiester bonds in the DNA backbone are broken.

2.b) A graph with the number of double-strand breaks on the x-axis and the average number of crossovers on the y-axis. Corn strains I, II, and III do not differ in their average number of crossovers because the error bars overlap.

2.c) Based on the data, as the average number of double-strand breaks increases, the average number of crossovers also increases.

2.d) The number of chromosomes most likely present in each of the four haploid cells is four. Since crossing over occurs between only three of the pairs, one pair of homologous chromosomes will not have a chiasma to hold them together. This will lead to an unequal distribution of chromosomes, with one cell receiving an extra chromosome and another cell lacking a chromosome. Plant breeders can use the information in Table 1 to help develop new varieties of corn by selecting strains with a higher number of crossovers, which will lead to greater genetic diversity in the offspring.