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Evolution > Sex and Linkage > Flashcards

Sex and Linkage Flashcards

1
Q

define alleles

A

A, a, B, b

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2
Q

define genotype

A

A/a; B/b

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3
Q

define haplotypes

A
  • gametes
  • AB, ab
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4
Q

define asexual reproduction

A
  • does not involve fusion of gametes
  • offspring inherits all genes from 1 parent
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5
Q

examples of asexual reproduction

A
  • binary fission
  • budding
  • vegetative
  • pathogenesis
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6
Q

asexual reproduction - angiosperms

A

many can simultaneously reproduce sexually and asexually

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7
Q

asexual reproduction: angiosperms - sexual and asexual examples

A
  • sexual: flowers, fruits, seeds
  • asexual: runners, leaflets
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8
Q

asexual reproduction - animals

A
  • some can reproduce by pathogenesis
  • where clones develop from unfertilized eggs
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9
Q

define hermaphrodites

A
  • animals that can produce sperm and eggs
  • can mate with them-selves (self-fertilization/selfing) or with another individual
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10
Q

pros of asexual reproduction

A
  • don’t have to rely on mate choice
  • no competition
  • reduced energy need
  • Fitness is doubled – all copies of your genes are passed vs sexual reproduction where you get half
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11
Q

explain selfing

A

they go through meiosis, but not outcrossing (randomly mating with other individuals)

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12
Q

define linkage equilibrium

A

the genotype of as chromosome at one locus is independent of its genotype at the other locus

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13
Q

define linkage disequilibrium

A

nonrandom association between a chromosome’s genotype at one locus and its genotype at the other locus

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14
Q

will selection at the A locus interfere with our ability to use HW models to predict evolution at the B locus?

A
  • yes
  • only if linked (at equilibrium)
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15
Q

what happens during meiosis

A
  • chromosomes segregate independently of one another
  • this means that loci A and B are inherited independently of one another
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16
Q

meiosis - linkage equilibrium

A
  • A and B are physically on the same chromosome, they are inherited independently because of recombination/crossing over during SEXUAL reproduction
  • haplotype frequencies are the same as expected
  • HW models can be used
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17
Q

meiosis - linkage disequilibrium

A
  • after recombination, haplotype frequencies are different than expected
  • HW models cannot be used
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18
Q

meiosis - what does it mean when a gene is linked

A

if two allele physically close, they are less likely to be broken up and tend to be inherited together

19
Q

what is genetic crossing over (recombination)

A
  • Occurs in prophase of meiosis I (ONLY in sexual reproduction)
  • Creates chromosomes with new combination of alleles for all genes one a chromosome
20
Q

explain the relationship between linkage and distance

A
  • disequilibrium decreases with physical distance between loci
  • close = more linked = less likely to be separated (higher disequilibrium, low equilibrium)
  • far = less linked = more likely to be separated (lower disequilibrium, higher equilibrium)
21
Q

what are the three mechanisms that can cause linkage disequilibrium

A
  1. selection on multilocus genotypes
  2. migration
  3. genetic drift/ population admixture
22
Q

why can the three mechanisms cause linkage disequilibrium

A

These can all produce populations in which some chromosome haplotypes are underrepresented and others are overrepresented compared to what you would expect with linkage equilibrium

23
Q

selection and linkage disequilibrium example

A
  • A and B together code for large body size which confers fitness advantage
  • creates linkage disequilibrium because these two alleles are more likely to be inherited together
  • they do not move closer to each other – each still has same locus
24
Q

selection and linkage disequilibrium example - what are the two allele an example of?

A

multilocus genotype bc 2 genes both code for the same trait

25
Q

genetic drift and linkage disequilibrium exmaple

A
  • Small population (drift is most effective)
  • Only have AB and Ab (no “a” present)
  • Mutation creates ab
  • We are missing a possible haplotype: aB
  • By definition this is LD bc its missing
26
Q

migration and linkage disequilibrium example

A
  • Population A and B are both LE but in different ways
  • When they mix (via migration), it creates LD
27
Q

what breaks up linkage disequilibrium

A
  • sex
  • Sexual reproduction involves meiosis with crossing over and random mating between different individuals
28
Q

linkage disequilibrium - define random mating

A

the union of gametes from unrelated parents brings together chromosomes with different haplotypes

29
Q

linkage disequilibrium - define crossing over

A

babies from random mating grow up and reproduce with crossing over, which breaks up old combinations of alleles and creates new ones

30
Q

linkage disequilibrium - define genetic recombination

A

the creation of new combinations of alleles during sexual reproduction

31
Q

linkage disequilibrium: genetic recombination - how does genetic recombination breakup disequilibrium

A

Genetic recombination randomizes genotypes at one locus with respect to genotypes at another → it reduces LD

32
Q

why do males exist?

A
  1. Genetic recombination breaks up linkage disequilibrium
  2. Genetic recombination pushes populations back towards Hardy-Weinberg Equilibrium
  3. Muller’s ratchet
  4. Red Queen
33
Q

why should asexual reproduction win over sexual reproduction

A
  • within each generation, each sexual female makes 2 daughters and 2 sones, each with 1/2 of her genes
  • each asexual female makes 4 daughters, each with 100% of her genes
  • the fraction of individuals in the population that are asexual females increase every generation
  • and the asexual females have higher fitness
34
Q

asexual always wins, if… (finish sentence)

A
  1. a female’s reproductive mode does not affect how many offspring she makes
  2. a female’s reproductive mode does not affect the probability that her offspring will survive
35
Q

why do males exist? - explain Muller’s rachet

A
  • mutation + drift
  • asexual populations occasionally sustains deleterious mutations
  • if a zero mutation group is small: chance events may cause its extinction
  • one mutation group may have highest fitness
  • but the loss of a group by drift if easier than is replacement by backmutation
36
Q

muller’s ratchet - define genetic load

A

the burden imposed by accumulating deleterious mutations

37
Q

example of Muller’s ratchet in the wild - Timema walking stick

A
  • 6 are asexual and 6 are sexual
  • researchers estimated ratio of non-synonymous to synonymous substitutions of important genes
38
Q

Muller’s ratchet: Timema walking stick example -what is the expectation

A
  • purifying selection eliminates deleterious alleles and leaves a signal
  • should make the ratio of nonsynonymous to synonymous mutations low
39
Q

Muller’s ratchet: Timema walking stick example - what is the result

A
  • it is consistent with Muller’s ratchet
  • bc asexual individuals had higher nonsynonymous to synonymous ration than sexual
  • thus sexual individuals have experienced purifying selection
40
Q

what is the Red Queen Hypothesis

A

individual must continually evolve new adaptations in response to other organisms adaptations to avoid extinction

41
Q

example for the Red Queen Hypothesis - snail

A
  • snails reproduce asexually or sexually
  • a higher proportion of females are asexual in more heavily parasitized population
42
Q

example of Red Queen Hypothesis - C. elegans

A
  • reproduce predominately asexually
  • they first treated all the worms with a chemical mutagen to generate variation
  • then they reared the populations in an environment w strong selection from pathogens
43
Q

why is sex adaptive

A
  • in a finite population
  • some will be missing due to sampling error
  • sex is adaptive bc it recreates these missing genotypes through segregation and recombination
44
Q

when may sex become disadvantageous

A
  1. bc asexual wins be numbers
  2. segregation and recombination break up advantageous genotypes they helped to create

Evolution (13 decks)

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