Download Genetic Variation

Genetic Variation
KEY CONCEPT
A population shares a common gene pool.
Genetic variation in a population
increases the chance that some
individuals will survive.
• Genetic variation leads to phenotypic variation.
• Phenotypic variation is necessary for natural selection.
• Genetic variation is stored in a population’s gene pool.
– made up of all alleles in a population
– allele combinations form when organisms have offspring
• Allele frequencies measure genetic variation.
– measures how common allele is in population
– can be calculated for each allele in gene pool
Genetic variation comes from several
sources.
• Mutation is a random change in the DNA of a gene.
– can form new allele
– can be passed on to
offspring if in
reproductive cells
• Recombination forms new combinations of alleles.
– usually occurs during meiosis
– parents’ alleles
arranged in new
ways in gametes
Genetic variation comes from several
sources.
• Hybridization is the crossing of two different species.
– occurs when individuals can’t find mate of own species
– topic of current scientific research
Genetic Variation
• Provide material for natural selection
• Brought about by mutation
• Provides genetic diversity
– Allows a species to adapt a new niche in its
environment
• Leads to natural selection
Phenotype
Phenotype
• The observable characteristic of an
organism such as coat color, eye
color or size.
• Can be caused by genes,
environmental factors, or a
combination of both.
Phenotype Variation
• Is a fundamental prerequisite for evolution by
natural selection. It is the living organism as a
whole that contributes (or not) to the next
generation, so natural selection affects the
genetic structure of a population indirectly via
the contribution of phenotypes. Without
phenotypic variation, there would be no
evolution by natural selection.
Phenotype and Natural Selection
• Phenotypes provide an outward appearance
for natural selections
– Example: The peppered moth color variation was
naturally selected according to the color of the
forest that it lives within.
– If the phenotype white is preferred in a light forest
then the black moths find it hard to survive to
reproduce thus leaving the white moths to
reproduce.
Phenotype Variation
• Environmental factors are things in an
organism's surroundings or lifestyle that can
influence it in various ways. For example, body
weight in humans may be influenced by
genes, but is also influenced by diet. In this
case, diet is an example of an environmental
factor
Phenotype Variation
• A lot more is known about the relationship
between genes and phenotypes. Let's take the
example of hair color. Perhaps there is a gene in
rabbits that codes for an enzyme that, in turn,
makes a brown-colored pigment in hair follicles.
Some rabbits may have genetic differences that
cause them to have more or less of this enzyme,
or enzyme that works more or less efficiently to
produce the pigment. We would expect these
rabbits to have different phenotypes, e.g. lighter
or darker brown hair, depending on these genetic
differences.