G&E: Speciation & Genetic Drift Flashcards

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1
Q

Speciation

A

The development of a new species from an existing species.

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2
Q

When does speciation occur?

A

When populations of the same species become reproductively isolated.

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3
Q

Reproductively isolated

A

Changes in the allele frequency cause changes in phenotype, which means populations of the same species can no longer interbreed to produce fertile offspring.

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4
Q

Allopatric speciation

A

Results from geographical isolation - when a physical barrier divides a population of a species, causing some individuals to become separated from the main population.

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5
Q

Sympatric speciation

A

When speciation occurs due to a population becoming reproductively isolated without any physical separation.

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6
Q

What does allopatric speciation require that sympatric speciation doesn’t?

A

Geographical isolation

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7
Q

Explain allopatric speciation:

A
  • Geographically separated populations will experience different conditions and selection pressures.
  • Different alleles will be more advantageous in different areas.
  • Directional selection will act then act on the alleles.
  • Allele frequency will change as mutations occur independently in each population.
  • Genetic drift may also affect the allele frequencies.
  • Differences accumulate in gene pools of separated populations, causing changes in phenotype frequencies.
  • Eventually, populations will have changed so much that they cannot breed to produce fertile offspring.
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8
Q

Explain sympatric speciation:

A

Random mutations could occur within a population, preventing members of that population breeding with other members of the species.

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9
Q

Reproductive isolation ocurs because changes in alleles and phenotypes in some individuals prevent them from breeding successfully.

What do these changes include?

A
  • Seasonal - individuals develop different flowering or mating seasons/become sexually active at different times of the year.
  • Mechanical - changes in genatalia prevent successful mating.
  • Behavioural - group of individuals develop courtship rituals that aren’t attractive to the main population.
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10
Q

Genetic drift

A

Chance, rather than environmental factors, dictates which individuals survive, breed and pass on alleles.

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11
Q

Evolution can occur because of what two things?

A

natural selection and variation

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12
Q

Explain how genetic drift can eventually lead to reproductive isolation and speciation:

A
  • Individuals within populations show variation in genotypes.
  • By chance, the allele for one genotype is passed on to the offspring more often than others.
  • No. of individuals with the allele increases.
  • Changes in allele frequency in two isolated populations could eventually lead to reproductive isolation and speciation.
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13
Q

When does evolution by genetic drift have a greater effect?

A

When population size is small - chance has greater infleunce.

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14
Q

Briefly describe how evolutionary change has resulted in diversity of organisms:

A
  • At the start, there was one population of organisms.
  • Population was divided and the new population evolved into separate species.
  • New species were divided again and new populations evolved into separate species.
  • Process has repeated over long periods of time to create millions of new species.
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