Download Biology CP 14.4 Gene Pools

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Gene Pools
Concept 14.4 pp. 310-316
Gene Pool
 Definition- consists of all the alleles in all the individuals
that make up a population.
 A population is the smallest level at which evolution can
 The gene pool is the reservoir of genes.
 It supplies the genetic variation for evolution.
 Sexual recombination- meiosis and fertilization provide
variety in offspring.
 Mutations & sexual recombination –random and cannot
be predicted.
Gene Pool
Definition- frequency of alleleshow often certain alleles
occur in the gene pool.
 Expressed as a decimal or
 Each plant has 2 alleles for
color- 20 total alleles.
14 red alleles (70%) and
6 white alleles (30%)
 Definition- evolution on a small scale
 generation to generation change in the allele
frequency within a population.
 Hardy-Weinberg Equilibrium Describes populations in which the gene pool does not
 Such populations have constant allele frequencies; are
not evolving.
 Rare for populations to remain in H-W equilibrium.
 Serves as a no-change baseline
Changes to a gene pool
 2 main factors-
 Genetic drift
 Natural Selection
 Genetic Drift-
 Definition-a change in the gene pool due to
 It is by chance which organisms will successfully
reproduce passing on alleles to the next
The first generation of the small wildflower population
illustrated consists of nine plants with red flowers (RR and Rr)
and one plant with white flowers (rr). It is partly chance that
affects which plants reproduce. By the third generation, no
plants carry the allele for white flowers. The result is a change
in allele frequencies in this population
 The smaller the population the greater the
impact of genetic drift.
 Larger populations are more stable.
 Reducing the size of a population reduces the size
of its gene pool and reduces genetic variation in a
 May affect a population’s ability to adapt.
 2 situations that drastically reduce the size of a
 Bottleneck Effect-disasters
 Founder Effect- new colonies
Bottleneck Effectearthquakes, floods, droughts, and fires
Marbles falling through
the narrow neck of a
bottle serve as an
analogy for the
bottleneck effect.
Compared to the
original population (in
the bottle) the new
population has less
Gene Flow
 The exchange of genes with another
 Migration of fertile individuals between
 Gene flow reduces genetic differences
between populations and could result in
a single population.
 Mutations- have a key role as the original
source of genetic variation for natural
 Especially important in asexually
reproducing organisms- bacteria.
 Biological Fitness- Contribution to the gene
pool of the next generation.
 Production of healthy, fertile offspring is
what counts in natural selection.
Darwin’s Finches
 Peter and Rosemary Grant’s Research
 30 yr. Study in the Galapagos.
 2 species of finches with different beak sizes.
 Their data related beak size to changes in environment- wet
and dry seasons and types of seeds available.
 Data provided evidence for natural selection occuring in a
shorter time span.
 Figure 14-31.
Grants’ Finches on Daphne Major