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Unit 4.6

Genetic variation within a species and geographical isolation leads to accumulated different genetic
information in a population and the potential to form new species.

Know the terms genotype, phenotype, gene, allele and locus.
Understand alleles can be dominant, recessive or co-dominant
Know that there may be multiple alleles…

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Heterozygous: both alleles of a pair of genes are different.

Co-Dominance and multiple alleles:

Co-dominance ­ in which both alleles are equally dominant
o Both alleles are expressed in the phenotype.
Multiple alleles ­ where there are more than two alleles, of which only two may be present
at the…

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Directional selection therefore results in phenotypes at one extreme of the
population being selected for and those at the other extreme being
selected against.
o Stabilising selection: selection may favour average individuals. This preserves
characteristics of a population.
If environmental conditions stay stable, the individuals with phenotypes
closest to the…

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Changes in ecosystems can lead to speciation; in southern California 10000 years ago a number of
interconnecting lakes contained a single species of pupfish. Increasing temperatures caused
evaporation and the formation of separate, smaller lakes and streams. This led to the formation of a
number of different species of pupfish.…


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