Week 3 Flashcards

1
Q

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

A
  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
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2
Q

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

A

one generation

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3
Q

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

A

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

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4
Q

What is the Human leukocyte antigen

A

a major histocompatibility locus in humans

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5
Q

What are HLA genes and how do they work

A

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

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6
Q

Do HLA genes have homozygote and heterozygote advantage

A

heterozygote advantage

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7
Q

Is the HLA locus of Humans in HWE

A

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

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8
Q

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

A

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

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9
Q

Directional Selection

A

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

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10
Q

Does directional selection cause a change in allele frequency

A

yes it will cause an increase in the favored allele

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11
Q

Stabilizing selection

A

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

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12
Q

Disruptive selection

A

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

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13
Q

Frequency dependent selection

A

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

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14
Q

Impacts of selection on phenotypic variation and allele diversity

A

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

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15
Q

What types of natural selection increase allelic diversity

A

heterozygote advantage, negative frequency dependent selection, disruptive selection

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16
Q

Genetic Drift

A

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

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17
Q

What can genetic drift lead to

A

stochastic loss of fixation of alleles, ultimately decreasing variation

18
Q

Does genetic drift affect variation more in larger or smaller populations

A

in smaller populations, genetic variation can be rapidly lost

19
Q

Javan Rhino

A

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

20
Q

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

A

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

21
Q

What processes or events can cause genetic drift

A

founder effect or bottlenecks

22
Q

What is the founder effect

A

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

23
Q

what does the founder effect and bottlenecks cause

A

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

24
Q

What is a bottle neck

A

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

25
What causes a bottleneck to be more severe
the longer the duration of the bottleneck and the more variation that is lost or the greater the decrease in population size
26
How have bottlenecks affected cheetahs
cheetahs have endured 2 bottlenecks and as such are so genetically similar that transplanting skin grafts doesn't evoke an immune response
27
Gene flow
aka migration: the movement of alleles form one population to another, occurs whenever individuals leave one population, join another, and then breed
28
what is the effect of gene flow between two populations
decreases genetic differences between them, homogenizes gene frequencies
29
Nonrandom mating
mating may not be random with respect to any particular gene in question. inbreeding and sexual selection are both examples of biased mating
30
Gene flow between African and euro-American people
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
31
Results of inbreeding
increases the frequency of homozygotes and reduces the frequency of heterozygotes in each generation, does not change allele frequencies
32
Inbreeding depression
a decline in average fitness that takes place when homozygosity increases and heterozygosity decreases in a population, does affect allele frequencies
33
causes of inbreeding depression
many deleterious mutations are recessive, at some loci there is an advantage to being heterozygous
34
Mutation
generates new alleles, its slow and random, can increase or decrease fitness
35
The red Queen Hypothesis
species must constantly evolve to avert extinction as a consequence of being out competed by other developing competitors
36
How can sexual species exist despite the twofold cost of sex
males help out, males compete decreasing deleterious mutations, genetic recombination
37
Effects of genetic recombination
can separate good mutations from bad mutations or unite multiple good mutations
38
Def: Isogamous
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
39
when does sexual selection occur
when individuals within a population differ in their ability to attract mates
40
What does sexual selection favor
individuals with heritable traits that enhance their ability to obtain mates
41
Sexual dimorphism
any trait that differs between males and females of the same species