Population Genetics

Question 1

what were the 2 early views on genetic variation ?

Answer 1

1. The classical hypothesis: (small genetic variation) populations have very little variation , heterozygotes are rare
2. The balance hypothesis: (lots of genetic variation)
   individuals are heterozygote at many loci and balancing selection maintains variability

Question 2

how is heterozygosity measured (calculation) ?

Answer 2

number of heteros/total number of individuals

Question 3

what is protein electrophoresis and direct DNA sequencing used for

Answer 3

it is used for determining an individual’s genotype and the diversity of population at a locus, protein electro was first DNA sequence is what is being used now

Question 4

what helped back the balance hypothesis and disprove the classical hypothesis ?

Answer 4

studies on protein electrophoretic

Question 5

what is the selectionist hypothesis and the neutral hypothesis ?

Answer 5

selectionist: balancing selection results in the maintenance of high genetic variability
Neutral: most alleles in natural populations are neutral ; doesnt affect fitness

Question 6

how to calculate the diploid Genotype Frequency

Answer 6

of individuals/ total population (N)

Question 7

how to calculate allele frequencies ?

Answer 7

homo is 2 x (# of individuals) ) + hetero 1 x (# of individuals) / 2 (N is total population)

Question 8

how would you calculate allele freq from genotype freq ?

Answer 8

F(A)= F(AA) + F (AB)/2
F(B) = 1 - F(A)

Question 9

what is a panmictic population ?

Answer 9

a randomly mating sexually reproducing population where each male has an equal probability of mating with each female and vice vera

Question 10

what is the HW principle ?

Answer 10

it a null hypothesis that tells us how allele and genotype frequencies act in a natural random mating population with no evolutionary forces that allows us to predict genotype frequencies from allele freq

Question 11

what is the HW principle equation and what does it do ?

Answer 11

p2+ 2pq+ q2 = 1 ; allows us to use allele freq to calculated EXPECTED genotype freq

Question 12

what are the 6 assumptions of hw principle ?

Answer 12

1. No selection
2. NO mutation
3. No migration
4. large population with random mate select ( panmictic)
5. diploid population
6. population reproduces sexually

Question 13

what is HW equilibrium and how does a population obtain it ?

Answer 13

HW equil is when genotype frequencies are equal to those expected based of HW principle and if they arent violating the 6 assumptions , genotype and allele frequencies will NOT change from one generation to the next it will remain the same

Question 14

what is alternate hypotheses ?

Answer 14

it represents a violation of some HW principle assumption

Question 15

how long does it take to put a population back to HW equilibrium ?

Answer 15

it will take a SINGLE generation of random mating to restore it

Question 16

what are the 5 steps with a given number of genotypes to check if you can reject the null hypothesis of HW x2eq?

Answer 16

1. calculate allele frequences
2. calculate expected genotype using HW calculation p2 and x 100 to get it out of percentage into a real number
3. plug it into X2
4. figure out degree of freedom
5. look at critical values of X2 chart if less we dont reject (in hw equil) it if greater we reject( not in hw equil

Question 17

what is the X2 equation?

Answer 17

sum (obs-exp)^2/exp of each expected genetoype

Question 18

what is degree of freedom calculation ?

Answer 18

DF= amount of genotypes - number of alleles

Question 19

what will HW disequilibrium be a result of and what can mess up HW equil

Answer 19

heterozygote deficit or heterozygote excess; both evolutionary and non evolutionary can mess up HW

Question 20

what 4 things can result in HW disequilibrium if violated ?

Answer 20

1. non random mating
2. migration
3. selection
4. not reproduces sexually

Question 21

what are the 3 consequences of violating HW principles ?

Answer 21

1. Change in allele frequencies
2. HW disequil
3. both change in allele freq and HW disequil

Question 22

can selection change the frequencies of allele from one generation to the next

Answer 22

yes but small but large overtime

Question 23

can an allele be removed from a population

Answer 23

no even if it is lethal it will still be hiding in heterozygotes

Question 24

what happens based on if an recessive lethal allele is common or rare ?

Answer 24

if it recessive common lethal allele freq will be different in the next generation
if ressesive rare lethal then allele frequency will be similar in the next generation

Question 25

how does fitness tie into dominant and recessive allele

Answer 25

if one allele is recessive and other is dominant the fitness of the heterozygote is equal to homozygotes it can also be codominant

Question 26

what can overdominance (heterozygote superioity) do in a population ?

Answer 26

it maintains the genetic diversity in a population

Question 27

what is a quantitative trait ?

Answer 27

it is phenotypic characteristic that varies continuously and it involves multiple loci ; characteristics controlled by multiple genes ex height by 6 loci vs 1 loci

Question 28

what are the 3 different modes of selection on quantitative traits ?

Answer 28

Directional Stabilizing Disruptive

Question 29

what is directional selection ?

Answer 29

increase or decrease of mean in population where population is at one extreme and DECREASES VARIATION in population , one trait is heavily prefered high or super low on 1 side

Question 30

what is stabilizing selection?

Answer 30

prior to selection within the population trait is in the middle post selection there is no to little impact on mean and DECREASE VARIATION

Question 31

what is disruptive selection ?

Answer 31

prior to selection high probability at both extremes , middle is low (U) AND INCREASE IN VARIATION little to no impact on mean post selection

Question 32

what is an example of directional selection

Answer 32

darwin's finch where draught survivors passed their characteristics to their offspring

Question 33

what is an example of stabilizing selection

Answer 33

a small golden gall a attacked by wasp and a big golden gall is attack by bird so being medium is perfect and decrease the chances of being attacked

Question 34

what is an example of disruptive selection ?

Answer 34

the back bellied seed cracker there is one type the feeds on small seed so need small beaks and some feed on big seeds so big beak so both are at the extremes

Question 35

even though directional and stabilizing are more common than disruptive why is there still so much phenotypic variation 3 reasons ?

Answer 35

1.balance between mutation and selection 2.disruptive may be more common 3. populations are not in evolutionary equilibrium

Question 36

does mutation not cause hw dis equil ?

Answer 36

mutation does not cause HW disequil even though its changing allele frequencies, it cause dis equil bc mutation occurs at the border of gamete and adult so when gamete randomly meet zygotes they will be in HW EQ.

Question 37

what is selective sweep ?

Answer 37

the rapid fixation towards 1 of a beneficial allele mutation by selection

Question 38

what is mutation-selection balance ?

Answer 38

new copies of deleterious alleles that (hiding in hetero) appear through mutation will equal the rate at which selection removes them

Question 39

what is heterozygote superiority(overdominance)

Answer 39

when a individual has two different alleles and is more likely to survival and maintain the alleles in CF