Selection

Question 1

Darwin’s Finches

Answer 1

an example of adaptive radiation/divergent adaption, where the variation was already present in the ancestral population but environmental influences (such as diet) dictated fitness in different descendent populations

Question 2

Natural Selection

Answer 2

process where some of the inherited genetic variation results in differences in individual’s ability to produce healthy offspring

Question 3

fitness

Answer 3

measure of an individual’s ability o survive and reproduce successfully

Question 4

Positive (Darwin) Selection

Answer 4

process where an advantageous mutation increases in a population

Question 5

Negative (purifying) Selection

Answer 5

process where a not-so-good mutation is removed from the population

Question 6

Does selection cause evolution?

Answer 6

NO - Selection only works on exisiting diversity. Evolution does not cause a new mutation to occur, but once it is there, then selection can act on it.

Question 7

Most common mutation?

Answer 7

neutral (no effect)

Question 8

Fixation

Answer 8

when the allele frequency = 1 –> 2 copies present in every member of the poulation

Question 9

What happens when the allele frequency equals 0?

Answer 9

the trait is lost from the population

Question 10

Least common mutation?

Answer 10

positive

Question 11

What can affect the rate that a trait rises to fixation?

Answer 11

dependent on the level of fitness advantage, initial allele frequency, and population size

Question 12

3 Examples of Traits with positive selection

Answer 12

1. Better ability to find/use food
2. Disease resistance
3. Improved fertility

Question 13

Convergent Adaptation

Answer 13

two separate populations develop the same variant independent of one another

Question 14

Heterozygote Advantage

Answer 14

where the heterozygotes have a higher fitness, and selection favors the maintenance of both alleles in a population via overdominant selection

Question 15

Examples of Heterozygote Advantage

Answer 15

1. Cystic fibrosis (1 copy resistant to typhus)
2. Sickle Cell anemia (1 copy resistant to malaria)

Question 16

Overdominant Selection

Answer 16

used in heterozygote advantage - think Africa and malaria

Question 17

Do populations subject to overdominant selection have a higher frequency of recessive disorders?

Answer 17

Yes (but often can be homozygous lethal anyway)

Question 18

How quickly are lethal mutations removed from the population?

Answer 18

Immediately. They’re dead, so

Question 19

Genetic Drift

Answer 19

changes in frequency of neutral variants

occurs by chance –> RANDOM, no selective pressure

Question 20

Can an allele reach fixation via genetic drift?

Answer 20

YES - bottlenecking, geographic isolation, stepping on a bug, and just time

Question 21

Are allele frequency changes more prominent in small or large populations?

Answer 21

small –> easy to eliminate an allele

Question 22

Genetic Drift vs. Selection

Answer 22

genetic drift is RANDOM

selection is NOT random and also directional in response to environmental pressures

Question 23

Artificial Selection

Answer 23

aka humans messing with things

can be done via phenotype or genotype, depending on availability and/or industry standards

Question 24

Pedigree Based Selection

Answer 24

Breed based on lineage, desirable traits should be passed down to offspring. Works well for simple traits but not anything more complex.

Question 25

Estimated Breeding Value (EBV)

Answer 25

quantification of the likelihood of an indivdual passing on the desired trait to their offspring

Question 26

Heritability (h^2)

Answer 26

proportion/percentage of a variation [of a trait] in the population due to genetic variation among individuals

(NOT percentage that is due to genetics)

Question 27

Heritability of a Mendelian trait?

Answer 27

1 (100%)

Question 28

Heritability of something caused entirely by environment?

Answer 28

0

Question 29

EBV Calculation for one trait

Answer 29

EBV = h^2(individual trait value minus the average trait value of the population)

Question 30

Index Merit/Score

Answer 30

Index = weighted sum of EBV for each objective trait (weight times EBV) added together

Question 31

Where do you get the weight for each trait?

Answer 31

importance of each trait to the producer/breeder/client

Question 32

Where do you get heritability?

Answer 32

many are published, but otherwise you have to make an educated guess

Question 33

Where do you get the individual’s trait value?

Answer 33

the owner or vet calulates it

Question 34

Correlated traits

Answer 34

selecting for one trait can often result in affecting another (can be desirable or undesirable)

ex: GSD and sloped back + hip dysplasia

Question 35

Indirect selection

Answer 35

improving one trait by intentionally selecting another trait known to correlate with it

Question 36

Inbreeding depression

Answer 36

a result of the increase of recessive diseases and generally associated with decreased performance

Question 37

Does inbreeding help with selection?

Answer 37

NO - inbreeding decreases genetic diversity, butselection can only act on the diversity that is present in a population

Question 38

Difference between marker-assisted selection (MAS) and GWAS?

Answer 38

just the number of markers - MAS selects for fewer quantitative trait loci (QTL), GWAS is the whole genome

Question 39

Marker Assisted Selection

Answer 39

uses genotypes of a set of markers/SNPs most strongly associated with one or a few QTL

Question 40

QTL (Quantitative Trait Loci)

Answer 40

GWAS done for a trait, looked at the regions of the genome associated with that trait, and selected a few markers/SNPs