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Key terms:. Species. A biological species is: a group of organisms that can interbreed and are reproductively isolated from other such groups. Each of these butterflies is a different species (there are thousands of different species of butterfly which do not interbreed). Populations.

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Key terms

Key terms:


Species

Species

  • A biological speciesis:a group of organisms that can interbreed and are reproductively isolated from other such groups.

  • Each of these butterflies is a different species (there are thousands of different species of butterfly which do not interbreed)


Populations

Populations

  • A biologist defines a population as:

    • the total number of one species in a particular area.

  • Populations can be very large and occupy a large area, with fairly continuous distribution.

  • Populations may also be limited in their distribution and exist in isolated pockets or “islands”, cut off from other populations of the same species.

Continuous distribution

Example: human population, Arctic tundra plant species

Fragmented distribution

Example: Some frog species


Gene pool

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Gene Pool

  • A gene pool is defined as the sum total of all the alleles for all the genes present in a population at any one time.

    • Not all the individuals will be breeding at a given time.

    • The population may have a distinct geographical boundary.

    • Each individual is a carrier of part of the total genetic complement of the population.

A gene pool made up of 16 individuals


Gene pool1

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Individual is homozygous recessive (aa)

Individual is homozygous dominant (AA)

Individual is heterozygous (Aa)

Gene Pool

Geographic boundary of the gene pool

A gene pool made up of 16 individual organisms with gene A, and where gene A has two alleles


How could a gene pool change

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Individual is homozygous recessive (aa)

Individual is homozygous dominant (AA)

Individual is heterozygous (Aa)

How could a gene pool change

Geographic boundary of the gene pool

A gene pool made up of 16 individual organisms with gene A, and where gene A has two alleles


Gene flow

Gene flow

  • Movement of alleles in and out of a gene pool due to individuals moving between populations


Genetic equilibrium

Genetic equilibrium

  • is when the gene pool is stable, the allele frequencies of a population remain unchanged from one generation to another

  • This occurs when there is a

    • Large population which is

    • Isolated (no migration or gene flow)

    • No mutations

    • Random mating

    • No natural selection


Demes

Demes

  • A species usually exists as distinct populations may be separated geographically. These local interbreeding populations are called demes.

  • Organisms mostly interbreed within the deme rather than with members of other populations, therefore, demes often develop slightly different allele frequencies, giving each different characteristics.


Species tricky to define

Species tricky to define

  • Boundaries of a species gene pool can be unclear .

    For example: closely related species of the dog family can interbreed

    Also, species can show a gradual change in phenotype over a geographical area. This gradual change is called a cline. This often occurs over the length of a country or continent.


Species1

No interbreeding

No interbreeding

Species

  • The boundaries of a species gene pool can be sometimes unclear, such as the genus to which all dogs, wolves, and related species belong:

Coyote–red wolf hybrids

Interbreeding

Interbreeding

Coyote

Canis latrans

Red wolf

Canis rufus

Inter-breeding

Inter-breeding

Domestic dog

Canis familiaris

Interbreeding

Interbreeding

Inter-breeding

Dingo

Canis familiaris dingo

Gray wolf

Canis lupus

Side-striped jackal

Canis adjustus

Black-backed jackal

Canis mesomelas

Golden jackal

Canis aureus


Key terms

Clines Species can show a gradual change in phenotype over a geographical area. This gradual change is called a cline. This often occurs over the length of a country or continent.


Ring species a special type of cline

Ring species – a special type of cline

If a cline forms a ring, (eg. across a continent) demes A and E may be unable to breed when they meet, although, the intermediate forms can still interbreed. Are A and E still the same species or two separate species?

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Sub species

Sub-species

  • These arise when populations show characteristics that are different from nearby populations. Sub-species can interbreed but this often occurs less frequently.This is normally because of geographical isolation.


Changing allele frequencies

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Changing Allele Frequencies

  • Mutation: Spontaneous mutations can alter alleles frequencies and create new alleles.

  • Gene flow: Genes can be exchanged

    with other gene pools as individuals

    move between them.

  • Small population size: Allele

    frequencies can change randomly

    from generation to generation.

    Natural selection: Selection pressure againstcertain alleles combinations may reduce reproductive success.

  • Non-random mating: Individuals seek outparticular phenotypes with which to mate.


Changing allele frequencies1

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Changing Allele Frequencies

Emigration

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Immigration

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Boundary of gene pool

Natural selection

Mutation

Mate selection (non-random mating)

Gene flow

Geographical barrier

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Genetic drift


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