Imagine that you have done a cross between two strains of yeast, one of which has the genotype a b c and the other a b c, where the letters refer to three rather closely linked genes in the order given. you examine many tetrads resulting from this cross, and you find two that do not contain the expected two b and two b spores. in tetrad l, the spores are a b c, a b c, a b c, and a b c. in tetrad il, the spores are a b c, a b c, a b c, and a b c. how have these unusual tetrads arisen?