Transcript evolution 4a - Hicksville Public Schools / Homepage

Aim: How does classical genetics
affect the theory of evolution?
Did Darwin know anything of
Mendel’s work of Classical
Genetics?
Darwin
Mendel
NO!!!! Darwin understood the connection between
natural selection and adaptation to the environment.
However, he could not explain how the variations that
are the basis for natural selection pass from one
generation to the next.
What was the result?
Population
Genetics
Remember, individuals do not evolve, populations do.
Natural Selection
+
Genetics
Population- a group of individuals of a single species
that live in a specific area.
What is Population Genetics?
The study of changes in the genetic makeup of
populations.
An important concept in population genetics is the
Gene Pool:
All the alleles (alternative forms of genes) in all the
individuals that make up a population.
What is the significance of a
population’s gene pool in
evolution?
The gene pool is the “reservoir”
from which the next generation
draws its genes.
The population’s gene pool is also
where genetic variation (the raw
material of evolution) is stored.
The phenotype
variation in of
phenotype
the offspring
(appearance)
are also determined
of this
population
by
the alleles
of flowers
in the gene
is determined
pool.
by the
combination of alleles in the gene pool.
What is Allele Frequency?
How often certain alleles occur in the gene pool (usually
expressed as a percentage).
R = 14/20 (70%)
r = 6/20 (30%)
The Hardy-Weinberg Law:
The condition in which allele frequencies do not change
from one generation to the next.
The population is said to be in genetic equilibrium.
Reproduction
alone does
notfollowing
affect
Ex:**Sexual
A population
of two individuals
has the
Genetic
Equilibrium
genotype: Rr and
Rr.
1)What is the allele frequency of R?
2)What is the allele frequency of r?
3)What are the predicted genotypes of their offspring?
4)What are the allele frequencies of the population of
the offspring?
Hardy-Weinberg Equation:
p2 + 2pq + q2 = 1 and p + q = 1
p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals
What happens when changes do
occur to the gene pool (frequencies
of alleles change) from one
generation to the next?
EVOLUTION
What leads to changes in the gene
pool?
1)Genetic Drift- a change in a gene pool due to
chance. **Causes changes in gene pools in small
populations.
2)Mutation- changes in DNA lead to changes in allele
frequency.
3) Gene Flow (Migration)- as individuals move into a
population, they bring in genes not already present.
As individuals move out of a population, they take
genes out of a population.
What leads to changes in the gene
pool?
4)Natural Selection- the reproductive success of
some organisms within a population can also change
allele frequencies (gene pool).
What conditions must be met for
the Hardy-Weinberg Law to hold
true?
The gene pool remains the same from generation to
generation.
1) The population must be large. In a small population,
alleles of low frequency may be lost due to genetic drift.
2)Individuals must not migrate into or out of a
population.
3)Mutations must not occur.
4)Reproduction must be completely random. This
means that every individual, whatever its genetic,
makeup, should have an equal chance of producing
offspring (no natural selection).
Why is the Hardy-Weinberg Law
useful when it can’t apply to real
world situations?
It is important because it allows us to discover
whether or not evolution is occurring in a population.
Change in allele frequencies
(gene pool)
=
Evolution
Microevolution- is evolution on the smallest scale –
a generation-to-generation change in the frequencies
of alleles within a population.
Macroevolution- major biological changes that are
clearly visible.