Lecture 6: Phenotypic Evolution (Part 2)

Question 1

Genotypic variation encoded in DNA is an example of what type of variation? Why?

Answer 1

Discrete, only four possible nucleotides

Question 2

Quantitative (phenotypic) traits such as height are which type of variation?

Answer 2

Continuous

Question 3

What two factors smooth out the phenotypic distributions?

Answer 3

More loci and more environmental variance

Question 4

What is the shape of the phenotypic variation curve?

Answer 4

Bell-shaped, normal distribution

Question 5

Are quantitative traits affected by few or many genes?

Answer 5

Many

Question 6

What do fitness functions describe/quantify?

Answer 6

How selection acts on quantitative traits

Question 7

What is correlational selection?

Answer 7

Selection that favors combinations of traits

Question 8

What is an example of a species that displays correlational selection?

Answer 8

Northwestern garter snake

Question 9

What are two traits in northwestern garter snakes that can be acted on by correlational selection?

Answer 9

Coloration (striped vs spotted)

Escape behavior (tendency to reverse course when escaping vs escaping in straight line)

Question 10

How many alleles does each locus have?

Answer 10

2

Question 11

What is the frequency of each allele of a locus?

Answer 11

1/2

Question 12

What is selection differential?

Answer 12

The difference between the mean of a trait in the existing population and the next generation

Question 13

What can selection differential be used to predict?

Answer 13

The amount of evolutionary change given directional selection

Question 14

What is the breeder’s equation? What do the variables mean?

Answer 14

deltaZ = h^2 x S

deltaZ: amount of evolutionary change in a trait

h^2: heritability of the trait

S: selection differential

Question 15

If h^2 = 0 …

Answer 15

Parents and offspring do not resemble each other

Question 16

If h^2 = 1 …

Answer 16

Parents and offspring are identical

Question 17

What is the role of h^2 in the graph of the breeder’s equation?

Answer 17

the slope of a regression line of the mean value of a trait from two parents and the value of the trait in their offspring

Question 18

The more positive h^2 is …

Answer 18

the more heritable the trait is between parents and offspring

Question 19

What is the equation for phenotypic variance? What do the variables represent?

Answer 19

Vp = Vg + Ve

Vp: overall phenotypic variance
Vg: genetic variance (phenotypic variation caused by genetic variation)
Ve: environmental variance components

Question 20

What can Vg depend on?

Answer 20

Age, tissue type, interactions among gene loci, and direct environmental influence

Question 21

What is the formula for genetic variance? What do the variables stand for?

Answer 21

Vg = Va + Vd + Vi

Vg: genetic variance
Va: additive genetic variance
Vd: Dominance variance
Vi: epistatic variance

Question 22

What is Va (additive genetic variance)?

Answer 22

The average effect of substituting one allele for another

Question 23

What is Vd (dominance variance)?

Answer 23

Variance due to dominance of alleles at the same locus

Question 24

What is Ve (epistatic variance)? What is epistasis?

Answer 24

Variance due to epistatic interactions of alleles at different loci

Epistasis is where the effect of one allele depends on another allele

Question 25

Which component of genetic variance contributes directly to evolutionary change?

Answer 25

Va

Question 26

When is a locus overdominant?

Answer 26

A heterozygote exhibits a phenotype different from either homozygote

Question 27

For most traits, which type of genetic variance is largest?

Answer 27

Va

Question 28

Do traits with high genetic variance have high or low heritability? What are some examples of such traits (2)?

Answer 28

High Height, length

Question 29

Do traits that require lots of resources have high or low heritability? Why? Examples (3)?

Answer 29

Low These traits are sensitive to environmental variation of those resources Body weight, litter size, puberty age

Question 30

True or false: A fluctuating environment can maintain variation and heritability.

Answer 30

True

Question 31

How is Isla Daphne an example of how fluctuating environmental variance maintain variation and heritability?

Answer 31

During low rainfall years, the food supply is low and most seeds are large/hard to crack, so body and bill sizes are large. After El Nino, there were lots of small, soft seeds available, so body and bill size dropped.

Question 32

What protein does the MC1r gene produce?

Answer 32

Melanocortin Receptor 1 (MC1r)

Question 33

What does the melanocortin receptor 1 regulate?

Answer 33

Melanin production in hair, feathers, and scales

Question 34

How is the MC1r gene an example of parallel phenotypic evolution?

Answer 34

Changes occur in different parts of the gene in different organisms but cause melanization in all of them

Question 35

Why do lesser snow geese exhibit a wide array of phenotypes rather than simply three?

Answer 35

There may be multiple copies of the MC1r gene

Question 36

Why do parasitic jaegers only have three phenotypes rather than a wide array?

Answer 36

There is only one copy of the MC1r gene