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Bio113: Evolution > Founder effects, Inbreeding and Hybrid zones > Flashcards

Founder effects, Inbreeding and Hybrid zones Flashcards

1
Q

When is drift strongest?

A

In smaller populations

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2
Q

What is a bottleneck?

A

a drastic reduction in the size of a population

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3
Q

What does a bottleneck cause?

A

a drastic change in allele frequencies

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4
Q

What is a founder effect?

A

a low genetic diversity caused by a population descending from a small number of colonising ancestors

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5
Q

What is a good example of a founder effect?

A

the Amish population

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6
Q

How many Amish are in Lancaster County?

A

12,000

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7
Q

Describe how the Amish are a good example of the founder effect

A

they come from an original population of 400

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8
Q

True of False

The Amish population support and carry out inbreeding

A

False

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9
Q

Why are the Amish an excellent study for geneticists? (4)

A
  • excellent genealogies (including new members)
  • large family sizes
  • restrcited populations
  • fixed gene pool (not many people enter the community)
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10
Q

What are the Amish gene frequencies like? Give two reasons why

A

Atypical

  1. founder effect
  2. further drift
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11
Q

Explain why drift is strong in the Amish population

A

there is a small population size

drift is stronger in smaller populations

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12
Q

Define stochastic and spell it

A

random

s-t-o-c-h-a-s-t-i-c

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13
Q

What type of change are changes in name frequencies and why?

A

Stochastic

they do not offer a selective advantange

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14
Q

Why do we study Y chromosomes and mitochondria?

A

They only come from one parent
Y chromosome: father
Mitochondria: mother

Stochastic changes (drift) are more likely to occur here because they do not offer a selective advantage

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15
Q

If selection is not occuring then what is?

A

Drift

Drift can occur by its self or with selection

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16
Q

Wilma Bias took a sample of blood from individuals in the Amish population. They were then analysed for changes and differences from the founders. What did her results show?

A
  • 100-150 gene loci
  • these loci had more changes than were expected
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17
Q

Give an example of a change that was found in the Amish populations loci

Also state by how much they changed

A

lots of changes found in allele frequencies controlling Rh factors

changed by 15-25%

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18
Q

What happens if the mother and child have different Rh factors?

A

if the mother has Rh- and the baby Rh+ then the mother’s immune system will attack the babies blood

mother is given anti-RhD IgD immunoglobulin which will destroy the babies Rh+ cells so there won’t be an immune response

Rh+ is selected against in this case

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19
Q

Describe Ellis-van Crevald syndrome

A
  • six fingered dwarfism
  • recessive disease
  • rare in overall population
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20
Q

In the Amish population what percentage of people are carriers of the diease and what is there genotype

A

13%

heterozygote

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21
Q

How can you work out how many people are heterozygotes? State the relevant equations

A

Hardy-Weinberg Equilibrium

P + Q = 1

P2 + 2PQ + Q2 = 1

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22
Q

Why are there more carriers of recessive diseases than those affected?

A

because heterozygotes will have the same fitness as the dominant homozygote

the recessive allele can therefore hide in a heterozygote and won’t be selected against

23
Q

Give examples of bottlenecks in nature (2)

A
  • after the last ice age (in the Pleistocene)
  • after the quaternary mass extinction event
24
Q

Give three causes of bottlenecks in nature

A
  1. ice ages
  2. humans
  3. climate change
25
Q

How are fish an example of a bottleneck? Use statistics

A

60% of fish are overfished

artificial bottleneck

loss of rare alleles

reduction in heterozygotes

26
Q

What animal is a good study of the effect of bottlenecks on genotypes?

A

Cheetahs

27
Q

What is the effect of bottlenecks on Cheetahs?

A
  • 95% of loci are homozygous
  • loss of genetic variation
  • skin grafts aren’t rejected - immune systems identical
  • fixed alleles
  • 82% of sperm has an odd form - high infertility rates
28
Q

What is meant by inbreeding?

A

non-random mating of relatives

29
Q

Why does inbreeding make the Hardy-Weinberg equilibrium invalid?

A

because one of the assumptions is that there is random mating

30
Q

Where is the chance of inbreeding the highest? What is the result of this?

A

Self-fertilising species

the populations would be mostly homozygotes

31
Q

What is identity by descent?

A

the relatedness between parents, f

32
Q

What can occur in identity by descent?

A

in an diploid the two copies of an allele, inherited by closely related parents, are the same and are therefore inherited from one ancestral individual

33
Q

True or False

Identity by descent and inbreeding are the same thing

Explain your answer

A

False

inbreeding icreases the chance of identity by descent but they are not the same thing

34
Q

Define consanguinity

A

blood relation

35
Q

What is the effect on a smaller population size on consanguinity? Explain your answer

A

nothing

it can occur in any population size

36
Q

What does consanguinity cause?

A

a change in allele frequencies

37
Q

What is an allele frequency cline?

A

a measurable gradient of a characteristic in a species over a geographical range

38
Q

What is a good example of a cline?

A

Biston Betularia (peppered moth)

39
Q

Describe the Biston Betularia

A

2 variations: melanic (black) and wild type (white)

melanic allele is dominant so fitness AA=AB

40
Q

What did the industrial revolution lead to? What would we expect the effect on the peppered moth to be?

A

the blackening of trees due to soot damage

we would expect selection for the melanic version

41
Q

In the Delmare forest near Manchester we did see black peppered moths but we also saw white Gonodontis Bidentata (scalloped hazel moths.) These moths are melanic in industrial centres like the peppered moth. Why is it that there are two different colour moths in the forest?

A

the different moths have different dispersion rates

peppered moth has a higher dispersion rate

it is seen further from the industrial centres than the scalloped moth

42
Q

What are hybrid zones?

A

areas where divergent, allopatric populations meet and interbreed

43
Q

What does sympatric populations mean?

A

occuring in overlapping geographical areas

44
Q

What does allopatric populations mean?

A

occuring in seperate non-overlapping geographical areas

45
Q

Hybrids are almost always heterozygote

What does this mean if there is underdominance selection occuring?

A

heterozygote disadvantage

they will not be selected for

46
Q

What occurs when heterozygote hybrids are as fit as parents?

A

weakening of reinforcement barriers

47
Q

What occurs when heterozygote hybrids are less fit?

A

strengthening of reinforcement barriers

48
Q

How many animals and plants are hybrids?

A

10% of animals

25-30% of plants

49
Q

What does strengthening of reinforcement barriers mean?

A

differences between species are stronger so mating individuals can easily tell one species from another

50
Q

Describe the bird experiment that shows strengthening of reinforcement barriers

A

male calling songs were played to birds from sympatric and allopatric areas

it was recorded how many females answered the call

sympatric areas (overlapping): no response to calls from other species

allopatric areas (non-overlapping): some females responded to other species call

51
Q

What does the bird experiment show? Why did some allopatric females answer the call?

A

where there is the chance that two species will meet and the hybrids they would produce are less fit then they are better at identifying their own species

allopatric species have not heard the call before so may become confused and answer the call

52
Q

What can weakening of barriers cause?

A

gene flow from parental populations into the hybrids

if this is high enough then speciation can occur

53
Q

Give an example of hybrid speciation

A

bats

specifically: A. Schwartzi

54
Q

Explain the bat hybrid speciation

A

one bat from the south

one bat from the north

met one one island and mated

mitochondrial evidence shows that the hybrid bat is a 3 way species but the third parent died out

Bio113: Evolution (3 decks)

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