Download Warm-Up 2/23/07

Warm-Up
2/23/07
• What are the 2 sources of Genetic Variation
that we talked about?
– Mutation
– Gene Shuffling (Sexual Reproduction)
• How many phenotypes are usually produced
by a single-gene trait?
– 2, a single gene trait generally has 2 alleles, like
the widow’s peak hairline in humans.
• How many phenotypes are usually produced
by a polygenic trait?
– More than two - usually many variations like
human height.
Warm-Up
2-26-07
In a population of mice, fur color is a single-gene trait controlled
by two alleles: B (black) and b (brown). B is dominant over b.
There are 8 homozygous black (BB) mice, 24 heterozygous
black (Bb) mice, and 18 homozygous recessive brown (bb)
mice.
1. How many total alleles are there in this population?
•
100
2. How many B alleles are there? How about b
alleles?
•
B = 40, b = 60
3. What is the Relative Frequency of B in this
population? How about the Relative Frequency of
b?
•
B = 40%, b = 60%
Warm-Up, continued
2-26-07
In a population of mice, fur color is a single-gene trait controlled by
two alleles: B (black) and b (brown). B is dominant over b. There
are 8 homozygous black (BB) mice, 24 heterozygous black (Bb)
mice, and 18 homozygous recessive brown (bb) mice.
1. How many black mice are there in this
population? And how many brown mice are
there?
•
Black = 32, Brown = 18
2. How is it possible that there are more black
mice than brown mice when the b allele for
brown has a higher Relative Frequency
than that B allele for black?
•
The heterozygous individuals have black fur, but
carry one b allele.
Challenge Question
• Lets say that being homozygous
recessive (bb) was lethal - all the baby
mice born with a bb genotype die before
they can reproduce.
• What do you think would happen to the
b allele in that population?
Warm-Up (Write the question
in your own words)
The plasma membrane of a cell
consists of
• A protein molecules arranged in two
layers with polar areas forming the
outside of the membrane.
• B two layers of lipids organized with the
nonpolar tails forming the interior of the
membrane.
• C lipid molecules positioned between
two carbohydrate layers.
• D protein
Brag Sheet
•
•
•
•
•
•
Name
GPA
Class Rank
Expected Graduation Date
Honors Classes
Extra curricular Activities
– Leadership
• Community Service
Evolution as Genetic Change
16.2
Natural Selection and
Genetics
Natural Selection leads to E_________
volution
• _________
• Natural Selection acts on the _____otype
Phen
– Why?
• But we know that an organism’s genetics
determine their phenotype
• In genetic terms, evolution is any change in
relative
alleles in a
the __________
frequency of _______
population’s gene pool.
Frequency of Phenotype
Normal Distribution of
Phenotypes
Phenotype (height)
Page 396, remember human height?
One of Darwin’s many
evolution ideas was:
A. Descent with modification (Current species descended from
previous generation, and each generation exhibited major
changes. Over time, large changes scale down to smaller
ones.)
B. Descent with modification (Current species descended from
previous generation, and each generation exhibited no
changes. Over time, small changes don't add up to large ones.)
C. Descent with modification (Current species descended from
previous generation, and each generation exhibited minor
changes. Over time, small changes add up to large ones.)
• The combined genetic information of all
members of a particular population is
the population’s
• phenotype.
• relative frequency
• genotype.
• gene pool.
Types of Selection
• Natural Selection can affect the
distribution of phenotypes in any of
three ways:
• Directional Selection
• Stabilizing Selection
• Disruptive Selection
Directional Selection
• When Natural Selection favors
phenotypes at one end of the curve.
The whole curve shifts in the direction of selection
Stabilizing Selection
• When Natural Selection favors
phenotypes near the center of the curve
Stabilizing Selection
Key
Low mortality,
high fitness
High mortality,
low fitness
Birth Weight
Selection
against both
extremes keep
curve narrow
and in same
place.
Disruptive Selection
• When Natural Selection favors
phenotypes at both ends of the curve.
Low mortality,
high fitness
High mortality,
low fitness
Population splits
into two subgroups
specializing in
different seeds.
Beak Size
Number of Birds
in Population
Key
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size
Results in two peaks with a dip in the middle.
Think
• There are three populations of mice in
the forest; white, grey, black.
• A hawk spots the white and black only.
• What happens to each population of
mice?
• What type of selection is working here?
• Graph the results
• Species of birds have short, medium,
and long beaks.
• The food source is insects in a tree.
• What beak will survive?
• What type of selection is this?
• Graph the results
Define
• Homologous structures
• Adaptation
Genetic Drift
• Genetic Drift is random changes in
allele frequencies.
• It relies on pure chance.
• Generally occurs in small populations
• Decreases genetic diversity in small
populations
• Lets look at an example
A small bag of marbles
Imagine that a small population is
represented by a bag of 20 marbles, 1/2
brown and 1/2 green. You only get to select 4
individuals from the popluation to reproduce
to form the next generation.
A small bag of marbles
We see in this example that, simply by
chance, the brown allele disappeared from
the population completely!
Lets try it ourselves!
The effects of Genetic Drift
on Diversity
• Generally has a big effect on small
populations
• Greatly reduces genetic diversity in
small populations
• What happens when a population loses
genetic diversity?
Warm-up
• Three people are walking through a
forest. One person is Andre the Giant,
another is Ms. Luna, and the third is the
little guy from Jacka**. The forest is full
of bushes and small trees. There is a
predator above the trees.
• Who will be killed? Why?
• What type of selection is this?