Lecture 6: Phenotypic Evolution (Part 2) Flashcards
Genotypic variation encoded in DNA is an example of what type of variation? Why?
Discrete, only four possible nucleotides
Quantitative (phenotypic) traits such as height are which type of variation?
Continuous
What two factors smooth out the phenotypic distributions?
More loci and more environmental variance
What is the shape of the phenotypic variation curve?
Bell-shaped, normal distribution
Are quantitative traits affected by few or many genes?
Many
What do fitness functions describe/quantify?
How selection acts on quantitative traits
What is correlational selection?
Selection that favors combinations of traits
What is an example of a species that displays correlational selection?
Northwestern garter snake
What are two traits in northwestern garter snakes that can be acted on by correlational selection?
Coloration (striped vs spotted)
Escape behavior (tendency to reverse course when escaping vs escaping in straight line)
How many alleles does each locus have?
2
What is the frequency of each allele of a locus?
1/2
What is selection differential?
The difference between the mean of a trait in the existing population and the next generation
What can selection differential be used to predict?
The amount of evolutionary change given directional selection
What is the breeder’s equation? What do the variables mean?
deltaZ = h^2 x S
deltaZ: amount of evolutionary change in a trait
h^2: heritability of the trait
S: selection differential
If h^2 = 0 …
Parents and offspring do not resemble each other
If h^2 = 1 …
Parents and offspring are identical
What is the role of h^2 in the graph of the breeder’s equation?
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
The more positive h^2 is …
the more heritable the trait is between parents and offspring
What is the equation for phenotypic variance? What do the variables represent?
Vp = Vg + Ve
Vp: overall phenotypic variance
Vg: genetic variance (phenotypic variation caused by genetic variation)
Ve: environmental variance components
What can Vg depend on?
Age, tissue type, interactions among gene loci, and direct environmental influence
What is the formula for genetic variance? What do the variables stand for?
Vg = Va + Vd + Vi
Vg: genetic variance
Va: additive genetic variance
Vd: Dominance variance
Vi: epistatic variance
What is Va (additive genetic variance)?
The average effect of substituting one allele for another
What is Vd (dominance variance)?
Variance due to dominance of alleles at the same locus
What is Ve (epistatic variance)? What is epistasis?
Variance due to epistatic interactions of alleles at different loci
Epistasis is where the effect of one allele depends on another allele
Which component of genetic variance contributes directly to evolutionary change?
Va
When is a locus overdominant?
A heterozygote exhibits a phenotype different from either homozygote
For most traits, which type of genetic variance is largest?
Va
Do traits with high genetic variance have high or low heritability? What are some examples of such traits (2)?
High
Height, length
Do traits that require lots of resources have high or low heritability? Why? Examples (3)?
Low
These traits are sensitive to environmental variation of those resources
Body weight, litter size, puberty age
True or false: A fluctuating environment can maintain variation and heritability.
True
How is Isla Daphne an example of how fluctuating environmental variance maintain variation and heritability?
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.
What protein does the MC1r gene produce?
Melanocortin Receptor 1 (MC1r)
What does the melanocortin receptor 1 regulate?
Melanin production in hair, feathers, and scales
How is the MC1r gene an example of parallel phenotypic evolution?
Changes occur in different parts of the gene in different organisms but cause melanization in all of them
Why do lesser snow geese exhibit a wide array of phenotypes rather than simply three?
There may be multiple copies of the MC1r gene
Why do parasitic jaegers only have three phenotypes rather than a wide array?
There is only one copy of the MC1r gene
