Transcript (Genetic Drift and Gene Flow) PPT File

Natural selection that
favors the average
variation in a gene pool.
Robins typically lay
four eggs. Larger
clutches may result in
malnourished chicks,
while smaller clutches
may result in no viable
offspring.
STABILIZING
SELECTION
Natural selection that
favors the ONE extreme
variation in a gene pool.
Anteaters lap up ants and
termites out of insect
mounds and hills using
their tongues.
Since this trait is
polygenic, there is a wide
array of tongue lengths.
What would be the best?
DIRECTIONAL
SELECTION
Natural selection that
favors the BOTH
extreme variations in a
gene pool.
On one of the tropical
Galapagos Islands there is
a species of lizard that
comes in a variety of sizes.
The small lizards can run
fast and easily hide under
rocks. The large lizards
have big enough claws to
climb the local trees.
DISRUPTIVE
SELECTION
Genetic Drift
• Genetic Drift – a random change in allele frequencies due to a chance
event
• It increases the chance of any given allele becoming more or less
prevalent
Genetic drift can have a much bigger impact on
smaller populations. (WHY?)
• Founder Effect – a type of genetic drift where few
individuals leave the original population to establish a new
one. They may or may not carry phenotypes that are
common to other members of the original population
• Bottleneck Effect – a type of genetic drift when a disturbance
greatly reduces the size of a population leaving a few
individuals to reestablish the population
•Disease/Pollution
• Habitat loss
• Predation/Hunting
Deforestation in the Amazon
Inbreeding: Possible bad side to genetic drift
• Mating among closely related individuals
• It tends to increase deleterious conditions, thus
leading to lower viability and survival rates.
• Everyone has 5-10 hidden disorder genes lurking in
your DNA
Reduced fertility both in litter size and
sperm viability
Increased genetic disorders
Fluctuating facial asymmetry
Higher infant mortality
Slower growth rate
Smaller adult size
Loss of immune system function
Video
The problem that all endangered or threatened
species encounter is this tendency to be forced
to “inbreed”. When there are only 100 of a
species left, and they are forced to
inbreed…then the tendency is for genetic
diversity to diminish even further.
So what??? Why is genetic diversity
important?
Another consequence of inbreeding in small
populations is that recessive and possibly fatal
combinations of alleles becomes greater.
Ethiopian Wolf
Genetic diversity gives
species the chance to
evolve. It provides enough
variation for possible
positive evolutionary
outcomes.. The smaller
the population, the less
likely that is to occur.
Gene Flow
• Genes move with individuals when they move
(emigrate or immigrate) into and out of a
population…and it changes the gene pool
• Phenylthiocarbamide (PTC) is not found in nature, but
the ability to taste it correlates strongly with the ability
to taste other bitter substances that DO occur in nature,
especially toxins.
It is believed that the ability to discern bitter tastes became a
benefit in human populations as an evolutionary mechanism to
protect early humans from eating poisonous plants.
Over time genetic drift, gene flow, mutations, and natural selection
has caused allelic frequencies to change amongst different
populations.
The world-wide ratio between tasters and non-tasters of PTC is at
roughly 70/30
In this lab you will be tasting papers that have been treated
with non-toxic chemicals.
The ability to taste any of these chemicals is genetically
transmitted and Dominant- so people who can taste are either
Aa or AA
PTC and Thiourea have very distinct flavors to people that
can taste them, and Sodium benzoate will taste differently to
different people
In this lab you will investigate the genetically-transmitted ability
or inability to taste certain chemicals in our population of
humans….and compare it to the world-wide ratio…
……..what is our population, you ask???…….
MOVE OUT OF THE
WAY INBREEDS AND
GENETICALLY
UNFORTUNATE….here
in Chaumonty-ville,
we’re sexy!
This population will consist of everyone in this room and the students in my other 3 AP
Biology classes.
Today you will try all three chemical papers and set up your first lab page.
We will document and analyze Chaumonty-ville’s data and compare it to the world-wide
ratio….
(Then analyze our class’ data as if we were in founder effect.)
In your lab book, make a Table of Contents entry for
Chaumonty-ville PTC Lab
• Title: Chaumonty-ville PTC Lab
• Question: (Write the question)
Does the ratio of Chaumonty-ville’s tasters/non-tasters
match with the rest of the world for PTC?
• Hypothesis: What do you think? Write your hypothesis here with WHY OR WHY NOT explanation.
• Personal Data: Write what YOU (not the class) could taste/not taste here and what that means as far as your
genotypes for those three genes.
PTC- taste/not taste, what that means about your genotype
Thiourea- taste/not taste, what that means about your genotype
Sodium Benzoate- taste/not taste, WHAT KIND OF TASTE, genotype?