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How Do Genes Make Evolution
Possible?
Essential Understanding
• The diversity of life is a result of ongoing
evolutionary change. Species alive today have
evolved from ancient common ancestors
Genotype vs Phenotype
• Typical plants and animals contain 2 sets of
genes, one from each parent
• Specific forms of a gene, alleles, vary between
individuals
• Genotype is a particular combination of alleles
whereas phenotype is the physical expression of
the genotype
Natural selection
• Natural selection acts on phenotype, not
genotype
• If an organism has a phenotype that is adaptive,
it may survive and pass the genes that code for
that trait to its offspring
Populations and gene pools
• A population is a group of individuals of the
same species in the same area
• A gene pool consists of all the genes that are
present in a population
• Allele frequency is the number of times an allele
appears in a gene pool
Allele Frequency
How many mice are
of each genotype?
BB –
Bb –
bb –
Evolution of populations
• Evolution involves a change in the frequency of
alleles in a population over time
Sources of Genetic Variation
• Mutations – Changes or mistakes in the genetic
code
• Genetic recombination – During sexual
reproduction, genes are often moved and
swapped
• Lateral gene transfer – Passing of genes between
individuals instead of through offspring
(Bacteria)
Single gene vs Polygenic Traits
• Single gene traits – Traits that are controlled by
a single gene – Presence or absence of
something
• Polygenic traits – Traits that are controlled by
more than one gene – Traits where there are
various levels
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