Transcript Evolution of A new Species

Evolution of A new Species
Genetic Variation
Sources of Genetic Variety
• The two main sources of genetic variation in a
population are mutations and sexual
reproduction
• Sexual reproduction shuffles parent genes/DNA
through meiosis
• Mutations create constant random variety that
sometimes makes an organism more fit for its
environment. EX: A mutation that gave brown
bears white fur in the polar regions making white
polar bears more fit for survival.
“What Molecules Do” Video
Mutations=Variety
Lethal Alleles
• How are lethal alleles maintained in a
population? Shouldn’t natural selection
remove these?
• Alleles that are lethal in a homozygous
individual may be carried in a heterozygous
individual.
• For example: If two parents
are carriers of a bad allele
and an individual inherits
both bad alleles they will get
the lethal disease.
Gene Pool• consists of all genes,
including all the
different alleles, that
are present in a
population.
Allele Frequency
• number of times an
allele occurs in a gene
pool
– EX: How many in this
class have at least one
dominant allele for
brown eyes
• Sexual reproduction
produces different
phenotypes, but it
does not change the
relative frequency of
alleles in a
population.
Gene Pool for Fur Color in Mice
How is evolution defined in genetic terms?
– In genetic terms, evolution is any change in the
relative frequency of alleles in a population.
What is Speciation
• Speciation is the formation of a new species
• Speciation is caused by reproductive isolation
– Reproductive Isolation is when two members of a
population cannot mate. There are 3 types of
reproductive isolation.
Reproductive Isolation
• #1. Behavioral Isolation is when genetically
similar populations are able to breed but
don’t due to differing mating rituals.
– http://www.youtube.com/watch?v=oYmzdvMoUU
A&feature=related
– http://www.youtube.com/watch?v=MPWOZZIzDy
o&feature=related
Reproductive Isolation
• #2. Geographic Isolation is when two
members of a population are separated by
barriers such as mountains, canyons, bodies of
water, etc.
• EX: Squirrels on opposite sides of the Grand
Canyon
Reproductive Isolation
• #3. Temporal Isolation is when members of a
population mate at different times of the year.
• EX: Different frogs mate in different months
Equilibrium
• Theoretical model of a population
• 5 Conditions:
1) No net mutations
2) NO immigration/Emigration
3) VERY large population
4) Individuals mate randomly
5)Selection doesn’t occur
The Equation
Hardy-Weinberg equilibrium=predict population
genotypes
p=dominant allele (A) q= recessive allele (a)
The sum of p+q=1,then solve p2 + 2pq + q2 = 1
p=dominant allele (A) q= recessive allele (a)
The sum of p+q=1,then solve p2 + 2pq + q2 = 1
Use the equation to solve this problem
What is p if q = 30%
p + .30 =1
p=.70
In this population what percent of individuals are
homozygous dominant (AA)?
p2= .72=.49=49%
In this population what percent of individuals are
heterozygous (Aa)?
2pq= 2(.7)(.3)= .42= 42%
Use the equation to solve this problem
What is p if q = 30%
p + .30 =1
p=.70
In this population what percent of individuals are
homozygous dominant (AA)?
p2= .72=.49=49%
In this population what percent of individuals are
heterozygous (Aa)?
2pq= 2(.7)(.3)= .42= 42%
-PRACTICE
Disrupting Equilibrium
• 1) Mutations- a change in DNA changes allele
frequencies
• 2) Gene flow- genes move in and out of the
population due to immigration and emigration
• 3) Genetic drift is a change in allele frequencies
• Genetic drift operates most strongly in small
populations
• 4) Non random mating- whenever individuals may
choose partners. Sexual selection occurs when
certain traits increase an individual’s success at
mating
• 5) 3 types of selection
Genetic Drift
• A random change in
allele frequency (can be
caused by fire, flood,
etc)
– In small populations,
individuals that carry a
particular allele may
leave more descendants
than other individuals
do, just by chance.
Genetic Drift
•Genetic Drift
Genetic drift
• Active art
• www.PHSchool.com
• Code cbp-5162
•Descendants
Genetic Drift
Population A
Population B
Founder effect
• Founder effect
• When allele frequencies
change as the result of
the migration of a small
subgroup of a
population.
• How does genetic drift differ from natural
selection in the way it changes the genetic
makeup/allele frequency of a species over
time?
Stabilizing Selection
Favors the formation of average/intermediate
traits.
Disruptive Selection
Favors extreme traits rather than average traits
Directional Selection
Favors the formation of a more-extreme trait.
Does Natural Selection act on the
phenotype or genotype of a species?
• Phenotype – predators
can only see the
outside physical
appearance of an
individual making them
less fit or suited for
their environment.