Evolution of Complex Traits Practice Problems

Compared to Bt-susceptible bollworms, Bt-resistant individuals have longer development times on normal cotton, but higher survival on Bt cotton. This means there's a trade-off between development time and survival. What would be the most likely consequence for the evolution of Bt-resistance without the longer development time?

Resistance would evolve more quickly, because it would not have an associated fitness cost.

Why should farmers growing Bt cotton reserve some space in their fields for normal cotton as a refuge?

The refuge reduces the fitness advantage of being resistant to Bt toxin.

The image below is from the video showing bacteria growing across a giant Petri dish with zones of increasing antibiotic concentration. The nodes (dots) represent places where researchers sampled, and color changes correspond to mutations for resistance in bacterial strains. Which of the following is demonstrated by the research results:

A. Mutations conferring antibiotic resistance happen because bacteria need them in order to survive.

B. Antibiotic resistance can evolve independently multiple times during a single experiment.

C. Individual bacterial cells can move long distances across the giant Petri dish.

D. There are concentrations of antibiotic drugs that no bacteria can survive.

B. Antibiotic resistance can evolve independently multiple times during a single experiment.

DDT is an insecticide that was used extensively in agriculture in the mid-1900s to kill many insect pests, including the boll weevil (pictured below), another pest of commercial cotton. DDT was initially effective at controlling boll weevil outbreaks, but after about a decade DDT became much less effective, because many populations of boll weevil had evolved resistance to DDT. Which of the following conditions would biologists say was required for the evolution of DDT resistance in a population of boll weevils:

A. Boll weevils in the population learned to adapt to the high levels of DDT in the environment.

B. The boll weevil population needed to evolve DDT resistance in order to avoid extinction.

C. A few boll weevils in the population were resistant to DDT before it was ever used.

D. Exposure to DDT caused specific, nonrandom mutations for DDT resistance within the population.

C. A few boll weevils in the population were resistant to DDT before it was ever used.

A population of cows has an average milk production of 20 liters per day. If we select the top 10% of cows with the highest milk production, resulting in a selection differential of 5 liters, and the heritability (h²) of milk production is estimated to be 0.3, what is the milk production of the next generation going to be?

S = 5 L

h2 = 0.3

∆Z = change in the mean = 5*0.3 = 1.5 L

New milk production = 20 + 1.5 = 21.5 L

Kinsey et al (2023) studied tail length and forelimb length in aquatic frogs (Xenopus laevis) from tadpole to adulthood. They were interested in whether a tradeoff existed across age. Specifically, they tested if a trait beneficial as a tadpole (longer tail) would be detrimental as an adult whereas a trait that is beneficial as an adult (like longer forelimb length) would be detrimental as a tadpole. The results of the adults are presented right. Which hypothesis is supported by this data:

A. Forelimb length and tail length are not correlated as adults; it is not beneficial to have a long tail as an adult.

B. Forelimb length and tail length are correlated as adults; it is sometimes beneficial to have a long tail as an adult.

B. Forelimb length and tail length are correlated as adults; it is sometimes beneficial to have a long tail as an adult.

If the phenotypic variance of apple trees grown in a controlled greenhouse is 3.3, what is the genetic variance of this population?

VP = 3.3

VE assumed = 0 because grown together in controlled environment

VG = 3.3

The broad sense heritability (H2) of body mass index (BMI) is 0.4.

a. If the variance in human BMI phenotype is 1.73, what is the genetic variance?

b. If the additive genetic variance is 0.02 and the epistatic genetic variance is 0.03, what is the dominance genetic variance?

c. What is the narrow sense heritability of this trait?

d. In a large-scale experiment, 5000 participants in a study on diet and weight loss consumed the same number of calories using the Mediterranean diet for 3 months. If participants lost an average of 6.8 lbs, what is the selection differential for the Mediterranean diet?

Two pumpkin varieties have a phenotypic variance of 7 and genetic variance of 1.

a. What is the broad sense heritability of this trait?

b. If the dominance genetic variance is 0.24 and the epistatic genetic variance is 0, what is the additive genetic variance?

c. What is the narrow sense heritability of this trait?

d. If the two varieties of pumpkin have a difference in size of 30 grams, what is the selection differential between the two varieties?

Flint corn is a variety of corn known for its hard skin and low water content, making the plant freeze tolerant. Originally cultivated in Mexico from teosinte, indigenous people were able to reduce the hardness of the skin from 91.47 to 54.17 over 9000 years.

a. If the narrow sense heritability of skin hardness is 0.77, what is the selection differential?

b. If the phenotypic variance is 1.2, what is the additive genetic variance?

c. If the genetic variance is 1.04 and the dominance genetic variance is 0.10, what is the epistatic genetic variance?

d. What is the broad sense heritability of flint corn?

e. If the specific environmental variance is 0.02 and the general environmental variance is 0.08, what is the GxE variance? Is flint corn phenotypically plastic?