Lecture 9

Question 1

Phenotypic variation & selection on phenotypes: Evolutionary processes

Answer 1

(such as natural selection) change the genetic makeup of populations (allele & genotype frequencies), but natural selection acts on the phenotype of an individual
must have a strong connection with the phenotype and genotype for evolution to happen

Question 2

Phenotypic variation & selection on phenotypes: response to selection depends on what?

Answer 2

depend the strength of the connection between the phenotype & the genotype

Question 3

What are many phenotypic traits

Answer 3

quantitative (= showing a continuous range of variation) (continuous range of variation)

Question 4

Quantitative traits are typically what?

Answer 4

polygenic (multiple genes)

Question 5

Artificial selection

Answer 5

vast amount of phenotypic variation and response to selection
start w pop with lots of variation it can respond to all kinds of things you want to select for
but of course there is a limit

Question 6

3 modes of natural selection in quantitative, continuous traits

Answer 6

not worried about genetic part, dont know mutation, quantitative

1) Directional selection–one phenotype extreme has the highest fitness
- not thing favored over another, very common

2) Stabilizing selection–the intermediate phenotype has the highest fitness
- whats favored isnt the most extreme but the intermediate (middle)
- eg: birth weight, goldilocks: its justtttt right)

3) Disruptive selection–the intermediate phenotype has the lowest fitness
- favors that extremes (what smallest and biggest, not the middle)

Question 7

Measuring the strength of selection: directional selection

Answer 7

strength of selection can be estimated by plotting relative fitness against trait values, and considering the slope (b) of the regression line.

Question 8

Measuring the strength of selection when the slope is 0

Answer 8

when measuring strength of selection we measure the slope

A slope of 0 = no selection
- no difference in trait value, no directional selection

The steeper the slope, the stronger the selection
- strong relationship, very steep will have biggest difference in trait value, produce significant change

Question 9

Example: Measuring the strength of selection on orange colour in guppies

Answer 9

y-axis is the relative fitness
x-axis is the amount of orange
slope is continuing to grow
B= 3.8

more orange= more offspring they will produce

Question 10

What will the response to selection will depend

Answer 10

depend on how much of the phenotype is heritable
- eg. no connection would be if the color orange did not get passed to offspring

Question 11

Heritability

Answer 11

the amount of phenotypic variation in a trait that is due to genetic variation
- eg. height

Question 12

how can we estimate heritability

Answer 12

by comparing a phenotypic trait in parents and their offspring
-> if there high heritably= strong connection/relationship

(see graph)
when heritability = 1.0
- all the dots are together and the line goes up (the slope of the regression line indicates heritability of the trait
- strong relationship, strong genetic basis
when when heritability = 0
- the line is flat and the dots are scattered everywhere
- each point represents the mean value of a phenogenetic trait in all offspring of two parents plotted against the mean parental value
- no relationship, no ability to predict offspring, no genetic basis