Bromeliads are plants that grow on the side of rainforest trees. Water
collects in the hollows of their leaves and forms long-lived pools, in which tree frogs lay their eggs and tinier organisms live out many generations.
In one such pool, a population of 105 Phantasmagoric Water Fleas is happily swimming about. Peering into the pool, you notice that 88 of them have short antennae, and 17 have long antennae. You hypothesize that long antennae might help their owners find food better and might be increasing in frequency in the population due to natural selection.
A literature search reveals that in the closely related species Fantastical Water Fleas, the gene Ant controls antenna length. You return and sequence the Ant gene in 105 Phantasmagoric Water Fleas. You find 2 alleles for this gene, which you name A1 and A2. The genotypes in the population are:
17 Fleas with A1A1, all with long antennae
48 Fleas with A1A2, all with short antennae
40 Fleas with A2A2, all with short antennae
1. Do you think the Ant gene controls antenna length in the Phantasmagoric Water Flea? Justify your answer using the terms "genotype" and "phenotype."
Hardy-Weinberg Equilibrium hypothesis testing:
To investigate your hypothesis (see second paragraph in the description above) about the selective advantage of long antennae, you decide to find out whether this population is in Hardy-Weinberg equilibrium.
2. Calculate the observed allele frequencies. Show your work.
Note: to avoid rounding error compounding over the rest of the problem, report p and q with 4 decimal places of precision. Use those values as you do the rest of the calculations.
3. Calculate the genotype frequencies you'd expect if the population were in Hardy-Weinberg equilibrium. Show your work. Give 4 decimal places of precision in your answers. Use those values in later calculations.
4. Using the expected genotype frequencies, calculate the number of Fleas with each genotype you'd expect in a sample this size (104 Fleas). Show your work. Round to the first decimal point.
5. What can you conclude from this about whether the population is in Hardy-Weinberg equilibrium?
6. What do you conclude about your selection hypothesis? Why?
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