4.4 Variation & Evolution Flashcards

1
Q

Define variation

A

Differences in the phenotype of a species

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2
Q

Describe the heritable variation

A
  • mutations in DNA base sequence or epigenetic modification
  • crossing of chiasmata at meiosis I, random assortment, gamete fusion
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3
Q

Discontinuous variation

A
  • no intermediates
  • monogenic
  • minimal environmental influence
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4
Q

Continuous variation

A
  • ranges ie height
  • polygenic
  • environment has an impact
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5
Q

Define selection pressures and list some examples

A

Environmental factors that can alter the frequency of alleles in a population when they are limiting
- nesting site availability, population density, predation, temperature, human impact

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6
Q

Define polymorphic

A

Occurrence of more than one phenotype in a population that cannot be accounted for by mutation alone

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7
Q

Define natural selection

A

The increased chance of survival and reproduction of organisms with phenotypes suited to their environment, e enhancing the transfer of favourable alleles from one generation to the next

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8
Q

Define the founder effect

A

The loss of genetic variation in a new population established by a very small number of individuals from a larger population

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9
Q

Define the Hardy-Weinberg principle

A
  • in ideal conditions, allele and genotype frequencies in a population are constant from generation to generation

p^2 + 2pm + q^2 = 1

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10
Q

Draw and explain stabilising selection

A
  • average phenotype provides great advantage than either extreme
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11
Q

Draw and explain directional selection

A
  • one extreme phenotype is selected against
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12
Q

Draw and explain disruptive/diversifying selection

A
  • average does not provide advantage so extremes are selected for
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13
Q

What are the conditions for Hardy-Weinberg

A
  • diploid organisms with equal allele frequencies in both species
  • random mating and sexual reproduction
  • large populations
  • no mutations or selections, and no emigration or immigration
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14
Q

Define a species

A

A group of phenotypically similar offspring that can interbreed and produce fertile offspring

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15
Q

What are the ways that new species arise?

A
  • polyploidy
  • isolating individuals
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16
Q

What is meant by a deme?

A

Sub group of a population

17
Q

Define reproductive isolation

A

The prevention of reproduction and gene flow between breeding groups within a species

18
Q

Briefly explain how speciation occurs

A
  • demes are isolated for many generations
  • undergo changes in allele frequency and accumulate so many mutations that they can no longer interbreed with the original population
19
Q

Differentiate between pre-zygotic and post-zygotic isolation

A
  • in pre-zygotic, gametes are prevented from fusing so the zygote never forms
  • in post-zygotic, gametes fuse and the zygote forms but the organism is sterile and cannot form gametes, so species don’t merge
20
Q

Define allopatric speciation

A

Evolution of a new species from demes isolated in different geographical locations

21
Q

Define sympatric speciation

A

The evolution of new species from demes sharing a geographical location

22
Q

Describe hybrid inviability

A
  • fertilisation occurs but incompatibility between genes of parents prevents embryo development
23
Q

Describe hybrid sterility

A
  • embryo of 2 diff species can develop
  • if chromosomes are not sufficiently similar, they cannot pair at prophase 1 so gametes cannot occur
  • sterility prevents gene flow so species remain distinct
24
Q

Describe hybrid breakdown

A
  • F1 hybrids are fertile but the F2 are sterile
  • incompatibility in nuclear genes and genes in mitochondria or chloroplasts