Week 3 - Population Genetics (Haploid)

Question 1

Biological definition of evolution

Answer 1

“the origin and alteration over generations of: the frequencies of genotypes within populations, the proportion of differentiated populations within species, the proportion of species with different traits within a lineage” (Futuyma and Kirkpatrick)

Could also add ideas within society

Question 2

natural selection definiton

Answer 2

the process whereby some individuals contribute more offspring to the next generation as a consequence of their carrying a trait or traits favorable to survival or reproduction

Question 3

evo. by natural selection occurs whenever: (3 things)

Answer 3

1. VARIANCE - individuals vary in some trait
2. SELECTION - individuals with some trait value are more likely to live and/or reproduce
3. HERITABILITY - parents have offspring with similar trait values

Question 4

is it easy to say a change in genotype is because of natural selection?

Answer 4

NO - easy to document a change but not to say bc of selection

Question 5

Haploid model of evolution

Answer 5

Variant alleles: A, a
Haploid population of size N, N = # of individuals in a population

Question 6

Selection definition

Answer 6

differential survival or reproduction of different entities

Question 7

p[t]

Answer 7

frequency of allele A at time t, from 0 to 1

Question 8

q[t]

Answer 8

frequency of allele a at time t, from 0 to 1

Question 9

p[t] + q[t] =

Answer 9

1

Question 10

Fitness definition

Answer 10

Avg. contribution per parent to the next generation, including survival and reproduction

Question 11

WA

Answer 11

fitness of A

Question 12

Wa

Answer 12

fitness of a

Question 13

equation for p[t+1]

Answer 13

= (WAp[t]) / {(WAp[t]) + Wa*q[t]}

Question 14

equation for evolutionary change across one generation

Answer 14

(WA - Wa)p[t]q[t] / {WA*p[t] + Waq[t]}

Question 15

If WA > Wa, when will change in p be greatest

Answer 15

in middle of change, when allele frequences are relatively similar (steepest part of the S curve)

Question 16

Relative vs absolute fitness

Answer 16

evolution by natural selection depends only on relative fitness not absolute values

Question 17

evolution after time t (p[t]

Answer 17

= (WA^t)p[t] / {((WA^t)p[t]) + (Wa^t)*q[t]}

Question 18

When would there be low genetic variance

Answer 18

When one allele is nearly lost, or nearly fixed

if p[t]* q[t] = variance, highest variance is when around 0.5, 0.5

Question 19

Haploid genetic variance

Answer 19

p[t] * q[t]

Question 20

What part of change over generation equation reps: 1. variance, 2. selection, 3. heritability

Answer 20

1. p[t]*q[t]
2. WA - Wa
3. p[t] (as A bearing parents pass A allele to offspring)

Question 21

if WA = Wa

Answer 21

p[t] remains at p[0] - neutral

Question 22

if WA> Wa

Answer 22

p[t] -> 1 - directional selection favouring A

Question 23

if WA < Wa

Answer 23

p[t] -> 0 - directional selection favouring a

Question 24

s

Answer 24

SELECTION COEFFICIENT - divide Wa and WA by Wa, typically done relative to the wildtype

so Wa = 1, and WA = 1 + s

Question 25

if s is 10 times smaller...

Answer 25

takes 10 times longer to observe same amount of frequency change

Question 26

W with a line over it [t]

Answer 26

mean fitness WAp[t] + Waq[t]

Question 27

mean fitness change across a generation

Answer 27

change in W bar = Wbar [t + 1] - Wbar [t]

Question 28

why hasn't everything evolved to be the same?

Answer 28

Fitness can change overtime environmental change the world isn't static organisms would never stay on evolutionary peak anyway even if our environment was static, because of mutation

Question 29

evolutionary factors other than natural selection

Answer 29

Mutations Chance Sex and recombination Alleles favoured for effects on some traits may affect others - PLEIOTROPY Neighbouring alleles in genome can be dragged with selected alleles