Question

this activity is a companion to the in - text figure \some alleles do not assort independently\ (figures 12.17a and b). be sure to review these figures before proceeding. after morgan and colleagues showed linkage of genes in fruit flies, biologists returned to studies on the pea plants that mendel had used. fortunately for mendel, the genes he chose were all unlinked. but the later studies showed anomalous results. consider crosses between heterozygous pea plants with the dominant phenotypes purple flowers (aa) and long pollen (bb) and homozygous recessive pea plants with red flowers (aa) and round pollen (bb). recall from chapter 12 that, in crosses like the one described above, the expected ratio of phenotypes in offspring if genes are unlinked is 1:1:1:1. what percentage of the seeds are expected to be purple and round under independent assortment? 50% 100% 25% 0%

Explanation:

Step1: Determine expected ratio under independent assortment

Under independent assortment, the cross between heterozygous pea - plants (AaBb) and homozygous recessive pea - plants (aabb) gives a phenotypic ratio of 1:1:1:1 for the four possible phenotypes. The four phenotypes are purple - long (AaBb), purple - round (Aabb), red - long (aaBb), and red - round (aabb).

Step2: Calculate the percentage

Since there are 4 possible phenotypes in equal proportions under independent assortment, the proportion of each phenotype is $\frac{1}{4}$. To convert this to a percentage, we use the formula $\text{Percentage}=\frac{1}{4}\times100\% = 25\%$.

Answer:

25%