1. In tomatoes, two alleles of one locus determine the character difference of purple versus green stems (alleles are P and p with P being completely dominant and coding for purple stems) and two alleles of a separate independent locus determine the character difference of "cut" versus "potato" leaves (alleles are C and c with C being completely dominant and coding for cut leaves).
You cross an individual that is PpCc with an individual that is homozygous recessive at both loci.
a. Determine the expected phenotypic and genotypic ratios, assuming independent assortment (genes are unlinked)? Please show your work.
The following progeny genotypes and phenotypes were observed: 25 PpCc (Purple, Cut), 25 ppcc (Green, Potato), 225 Ppcc (Purple, Potato), 225 ppCc (Green, Cut). Does this fit your expectation for phenotypic ratios if the genes are assorting independently? If not, what could explain this result? If the genes are linked, what is the arrangement of the genes on a particular chromosome for the double heterozygote?
2. You observe the following numbers of individuals of each genotype in a population:
AA Aa as
700 200 100
a. What are the observed genotype frequencies in this population?
b. What are the allele frequencies in this population?
c. What are the expected Hardy-Weinberg genotype frequencies?
d. What is the expected number of individuals of each genotype?
e. Do a chi-square test and provide whether you reject or fail to reject the null hypothesis. Is this population in H-W equilibrium? If you reject that this population is in H-W, what might be the cause?
3. As discussed in class, Daphnia have inducible defenses in response to chemical cues from a predatory midge including the production of thicker exoskeleton and head teeth. Some lakes with Daphnia have the predatory midge whereas some lakes with Daphnia do not have the predator. Develop an hypothesis about whether inducible defenses would be more likely in predator-free or predator-present populations and design a simple experiment to test this hypothesis.