Exam 3: Population and Evolutionary Genetics II

Question 1

forces of evolution: natural selection

Answer 1

is the differential survival and REPRODUCTION of individuals due to differences in phenotype

Question 2

forces of evolution: nonrandom mating

Answer 2

occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals

Question 3

forces of evolution: mutation

Answer 3

is a permanent alteration in the DNA seqs that makes up a gene

Question 4

forces of evolution: migration

Answer 4

is the movement of populations, groups or individuals; in genetic terms: MIGRATION ENABLES GENE FLOW the movement of genes from one population into another

Question 5

forces of evolution: genetic drift

Answer 5

is the change in the frequency of a gene variant (allele) in a population due to random sampling of organisms.

Question 6

what is evolution

Answer 6

environmental forces that cause change in gene frequency in a population over time

Question 7

nonrandom mating-sexual selection

Answer 7

occurs when members of one biological sex choose mates of the other sex to mate with and compete w/ members of the same sex for access to members of the opposite sex

Question 8

reinforcing sexual selection with the Irish elk

Answer 8

detrimental; their antlers became so large, through reinforcing sexual selection (females like these large antlers) that the bulls eventually could not carry on the normal business of life and so became extinct

Question 9

forward and reverse mutation rates can change

Answer 9

allele frequencies but eventually lead to a stable equilibrium if mutation rates remain constant (fwd=reverse)

Question 10

an influx of genes from an outside population can

Answer 10

dramatically change allele frequencies; the amt of change in allelic frequency due to migration btwn populations depends of the difference in allelic frequency and the extent of migration

Question 11

an example of human gene flow

Answer 11

certain seqs are associated with human mito, which are groups of seqs (nucleotide variations in mito) that tend to be close together and recognizable as patterns. can follow where mito seqs arose from if have enough information (genetic seqs from around the world). Seq populations from all over the world can follow female migration as most mito is passed maternally

Question 12

human gene flow and the Y chromosome

Answer 12

by looking at the few sequences on the Y chromosome, can follow migration patterns of men; often reflects invasions/wars ( a lot of the outflow from Asia was a consequence of gene flow with armies moving around the world) not always conquering armies

Question 13

define genetic drift

Answer 13

variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce
(random accumulation of genes due to unpredictable chance happenings typically in small pops)

Question 14

what are the 2 causes of genetic drift

Answer 14

founder effect and genetic bottleneck

Question 15

define founder effect

Answer 15

the reduced genetic diversity that results when a population is descended from a small # of colonizing ancestors (reduce the amt of individuals that are breeding)

Question 16

define genetic bottleneck

Answer 16

is a sharp reduction in the size of a population due to environmental events (earthquakes, floods, fires, disease, or droughts) or human activities (such as genocides)
sml # of indivs and stuck with what little genetic variation that is there

Question 17

populations diverge at random in _ and can become _

Answer 17

at random in allelic frequency and can become fixed for one allele as a result of genetic drift -especially when the population is small

Question 18

what effect does genetic drift have on the genetic composition of populations?

Answer 18

as a result of genetic drift, allelic frequencies in the different populations diverged and often became fixed for one allele or the other

Question 19

natural selection: fitness

Answer 19

is the relative reproductive success of a genotype compared to other genotypes in the population

Question 20

fitness ranges from

Answer 20

0 to 1

Question 21

to calculate fitness

Answer 21

(avg # of offspring produced by a genotype)/(avg # of offspring produced by the most prolific genotype)

Question 22

natural selection: selection coefficient

Answer 22

is the relative intensity of selection against a genotype

Question 23

selection coefficient equals:

Answer 23

1 - the fitness for a particular genotype

Question 24

the results of selection: (2)

Answer 24

1. directional selection

2. overdominance vs underdominance

Question 25

directional selection

Answer 25

a type of selection in which one allele or trait is favored over another

Question 26

evolution through natural selection can occur remarkably quickly when

Answer 26

selection pressure is very strong and reproductive rates are fast. ex bacteria and antibiotic resistance

Question 27

overdominance

Answer 27

(heterozygote advantage) heterozygotes are favored over either of the homozygotes and have a reproductive advantage (each allele has a diff fcn) which maintains both alleles in the population

Question 28

underdominance

Answer 28

(heterozygotes selected against) the heterozygote has a lower fitness than both homozygotes. this leads to an unstable equilibrium

Question 29

t/f: advantage to have 2 different alleles rather than be homozygous

Answer 29

true

Question 30

heterozygosity for sickle disease provides a reproductive advantage in regions with high levels of malaria?

Answer 30

yes; hets for sickle Hb have an advantage in parts of world where malaria is common bc parasite does not do well in blood where part of the RBC have sickle Hb. hets live longer bc resist malaria and pop incr who carry sickle cell allele

Question 31

selection pressures on heterozygotes leads to

Answer 31

isolation; pure breeding lines that are reproductively isolated

Question 32

in tropical Africa, where malaria is common: homozygous dominant (normal)

Answer 32

die of malaria, very susceptible (1/4)

Question 33

in tropical Africa, where malaria is common: homozygous recessive

Answer 33

die of sickle cell anemia, less susceptible to malaria bc of 2 copies of sickle cell Hb (1/4)

Question 34

in tropical Africa, where malaria is common: heterozygote carriers

Answer 34

are relatively free of both; some of the symptoms but much less susceptible to malaria and where malaria is common, these ppl live longer and reproduce/survive more and more common in population (1/2)

Question 35

natural selection produces species that are

Answer 35

uniquely adapted to their environment

Question 36

polar bears and environmental changes?

Answer 36

polar bears they are uniquely and perfectly adapted to an ice world environment thus not that much variation bc have been adapted. when the environment starts to changes two things could happen: 1. extinct (could not adapt) 2. if over a long enough period of time the genetic variation can accumulate and the pop will shift to match the environment (evolution)

Question 37

genetic signatures of exceptional longevity in humans

Answer 37

evaluate centenarian populations to learn important info about human genetic variation and what contributes to longevity (if live a long time 100+ yrs) what are the genetic variants these people share? show variants associated with alzheimer’s and CVD (less susceptible to these bc of variants) accumulation of really good variants that make them robust and live a long time

Question 38

mutation short-term effect

Answer 38

change in allelic frequencies

Question 39

mutation long-term effect

Answer 39

equilibrium reached btwn forward and reverse mutations

Question 40

migration short-term effect

Answer 40

change in allelic frequencies

Question 41

migration long-term effect

Answer 41

equilibrium reached when allelic frequencies of source and recipient population are equal

Question 42

genetic drift short-term effect

Answer 42

change in allelic frequencies

Question 43

genetic drift long-term effect

Answer 43

fixation of one allele

Question 44

natural selection short-term effect

Answer 44

change in allelic frequencies

Question 45

natural selection long-term effect (3)

Answer 45

1. directional selection: fixation of one allele
2. overdominant selection: equilibrium reached
3. underdominant selection: unstable equilibrium

Question 46

small populations and the study of genetic variation (Mennonites)

Answer 46

Mennonites stay w/in one community and have unique collection of genetic variation. useful for understand origin of many different genes that contribute to developmental problems.

Question 47

consequence of closed community

Answer 47

study the origin of certain types of diseases bc there is a higher frequency of developmental problems w/in these restricted populations

Question 48

although they may exert a greater impact on risk, few rare disease variants have been found, owing to the greatly increased sample sizes that are typically necessary to demonstrate association with rarer variants. one alternative strategy is to _

Answer 48

study isolated populations, where historical bottlenecks reduce genetic diversity and some otherwise rare variants may drift to higher frequencies

Question 49

characteristics of isolated populations

Answer 49

derived from a relatively small # of individuals aka founders; founders who became isolated and/or experienced a bottleneck ie a reduction in population size. Often endogamy incr and gene flow diminishes

Question 50

in context of a small, reproductively isolated population, alleles fluctuate randomly toward _

Answer 50

toward higher and lower frequencies (genetic drift). this may incr frequency of ancestrally rare alleles, but more often these alleles disappear entirely, leading to a rapid and important reduction in genetic diversity

Question 51

genetic drift also contributes to

Answer 51

increased homozygosity

Question 52

a population bottleneck coupled with random genetic drift can create:

Answer 52

local concentrations of otherwise rare traits and diseases (founder effect)

Question 53

another characteristic of isolated populations is a large increase in linkage disequilibrium leading to:

Answer 53

long stretches of shared chromosomal regions or haplotypes