Week 3

Question 1

How can we test if a locus is in HWE if there are co-dominant alleles

Answer 1

1. record genotype frequencies by observation
2. calculate allele frequencies from the observed genotype frequencies
3. use the allele frequencies to calculate the expected genotype frequencies assuming HWE
4. compare the observed and expected genotype frequencies

Question 2

How many generations does it take to cause departure or consistency from HWE

Answer 2

one generation

Question 3

In the MN blood example explored in class what were the findings

Answer 3

each population did not depart form HWE
the allele frequencies across populations varied

Question 4

What is the Human leukocyte antigen

Answer 4

a major histocompatibility locus in humans

Question 5

What are HLA genes and how do they work

Answer 5

cell surface protiens that are encoded for by genes on chromosome 6 that bind to antigens and then present them on the outside of cells so the cells can be recognized by the immune system

Question 6

Do HLA genes have homozygote and heterozygote advantage

Answer 6

heterozygote advantage

Question 7

Is the HLA locus of Humans in HWE

Answer 7

No, experimentation has shown that there are more heterozygotes observed than expected by chance, meaning at least one assumption was violated

Question 8

What is heterozygote advantage and what needs to be true about the alleles for it to be in effect

Answer 8

a pattern of natural selection in which heterozygous individuals have higher fitness than homozygous individuals. The associated alleles must be co-dominant for there to be a different phenotype associated with the heterozygous individual

Question 9

Directional Selection

Answer 9

Changes the average value of a trait one of either two directions
-extreme phenotype is favored causing shift

Question 10

Does directional selection cause a change in allele frequency

Answer 10

yes it will cause an increase in the favored allele

Question 11

Stabilizing selection

Answer 11

reduces variation in a trait among a population
-intermediate phenotype favored

Question 12

Disruptive selection

Answer 12

maintains or increases the amount of variation in a trait
-both extremes are favored

Question 13

Frequency dependent selection

Answer 13

Negative FDS: fitness is highest in rare phenotypes
Positive FDS: fitness is highest in common phenotypes

Question 14

Impacts of selection on phenotypic variation and allele diversity

Answer 14

different types of natural selection can increase, maintain or decrease phenotypic variance, allele diversity and number of alleles

Question 15

What types of natural selection increase allelic diversity

Answer 15

heterozygote advantage, negative frequency dependent selection, disruptive selection

Question 16

Genetic Drift

Answer 16

any change in allele frequencies in a population due to chance, unbiased with respect to fitness

Question 17

What can genetic drift lead to

Answer 17

stochastic loss of fixation of alleles, ultimately decreasing variation

Question 18

Does genetic drift affect variation more in larger or smaller populations

Answer 18

in smaller populations, genetic variation can be rapidly lost

Question 19

Javan Rhino

Answer 19

originally widespread in SE Asia, slowly going extinct, first in India in 1925 then in Vietnam in 2010 now only population is in ujung kulon with about 60 individuals

Question 20

What percentage of primates are threatened extinct and what percent have declining populations and why is this the case

Answer 20

60% are threatened with extinction and 75% have declining populations
mostly due to habitat loss

Question 21

What processes or events can cause genetic drift

Answer 21

founder effect or bottlenecks

Question 22

What is the founder effect

Answer 22

cultural isolation causes the smaller population to have a subset of the genetic variation of the original population

Question 23

what does the founder effect and bottlenecks cause

Answer 23

a decrease in the number of alleles but an increase in the frequency

Question 24

What is a bottle neck

Answer 24

its an event in which a population decreases in size for a period of time before increases back to normal population size

Question 25

What causes a bottleneck to be more severe

Answer 25

the longer the duration of the bottleneck and the more variation that is lost or the greater the decrease in population size

Question 26

How have bottlenecks affected cheetahs

Answer 26

cheetahs have endured 2 bottlenecks and as such are so genetically similar that transplanting skin grafts doesn’t evoke an immune response

Question 27

Gene flow

Answer 27

aka migration: the movement of alleles form one population to another, occurs whenever individuals leave one population, join another, and then breed

Question 28

what is the effect of gene flow between two populations

Answer 28

decreases genetic differences between them, homogenizes gene frequencies

Question 29

Nonrandom mating

Answer 29

mating may not be random with respect to any particular gene in question. inbreeding and sexual selection are both examples of biased mating

Question 30

Gene flow between African and euro-American people

Answer 30

Biased mate pairing can be observed by looking at the gene flow of contemporary African Americans where there is a greater percent of European contribution in the Y chromosome suggesting the female Africans reproduced with White males more often than the other way around

Question 31

Results of inbreeding

Answer 31

increases the frequency of homozygotes and reduces the frequency of heterozygotes in each generation, does not change allele frequencies

Question 32

Inbreeding depression

Answer 32

a decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in a population, does affect allele frequencies

Question 33

causes of inbreeding depression

Answer 33

many deleterious mutations are recessive, at some loci there is an advantage to being heterozygous

Question 34

Mutation

Answer 34

generates new alleles, its slow and random, can increase or decrease fitness

Question 35

The red Queen Hypothesis

Answer 35

species must constantly evolve to avert extinction as a consequence of being out competed by other developing competitors

Question 36

How can sexual species exist despite the twofold cost of sex

Answer 36

males help out, males compete decreasing deleterious mutations, genetic recombination

Question 37

Effects of genetic recombination

Answer 37

can separate good mutations from bad mutations or unite multiple good mutations

Question 38

Def: Isogamous

Answer 38

all individuals in a species produce gametes that are the same size and therefore sexual selection does not occur given that both parents are equally contributing

Question 39

when does sexual selection occur

Answer 39

when individuals within a population differ in their ability to attract mates

Question 40

What does sexual selection favor

Answer 40

individuals with heritable traits that enhance their ability to obtain mates

Question 41

Sexual dimorphism

Answer 41

any trait that differs between males and females of the same species