Download Chapter 23 Reading Guide – The Evolution of Populations 1. Define

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Chapter 23 Reading Guide – The Evolution of Populations
1. Define the following terms:
a. Microevolution
b. Population genetics
c. Modern synthesis
d. Gene pools
2. Explain the Hardy-Weinberg theorem.
3. Write and explain the Hardy-Weinberg equation.
4. List the five conditions for Hardy-Weinberg Equilibrium.
5. Name and explain the two processes that produce variation and make evolution possible.
6. Define the following:
a. Genetic drift
b. Bottleneck effect
c. Founder effect
d. Gene flow
7. Use the key provided to identify the microevolution cause described in each of the following.
A. Bottleneck effect
D. Mutation
B. Founder effect
E. Nonrandom mating
C. Gene flow
F. Natural selection
______ Changes in the gene pool of a small population due to random chance
______ Examples of genetic drift
______ Much of the population is wiped out by a natural disaster; the allele frequency of the population
is determined by a small surviving population
______ A few individuals colonize a new habitat; genetic drift in a new colony
______ Change in the gene pool of a population due to the migration of fertile individuals or the transfer
of gametes between populations
______ The introduction of new alleles
______ Mates not chosen randomly; sexual selection
______ Differential reproductive success; some phenotypes selected against; individuals best adapted to
the environment survive to reproduce and pass their genes onto the next generation
______ The appearance of blue M&Ms in a population of red and green M&Ms
A. Bottleneck effect
B. Founder effect
C. Gene flow
D. Mutation
E. Nonrandom mating
F. Natural selection
______ A few birds separate from the rest of the flock, fly to a new area, and establish a new colony
______ At the end of the last ice age, cheetahs almost became extinct – only a few survived.
______ Only a small number of flies survives a harsh winter.
______ Female flies prefer to mate with white-eyed males
______ Pollen from one field of seed corn is blown across the county to another field of seed corn.
8. Name and explain the three ways that the frequency distribution of heritable traits can be altered by
natural selection. Draw a graph to illustrate each.
9. Use the key below to identify the mode of natural selection described /represented by each of the
following:
A. Stabilizing selection
B. Directional selection
C. Disruptive selection
D. Sexual selection
______ acts against the extremes
______ favors both extremes
______ favors one of the extremes
______ favors the intermediate
______ reduces the intermediate
______ reduces phenotypic variation
______ females select males that are showier, more colorful, etc. for mating
A. Stabilizing selection
C. Disruptive selection
B. Directional selection
D. Sexual selection
______ a plant population is found in an area that is becoming more arid; the average surface area of the
leaves had been decreasing over generations
______ female chickens prefer to mate with roosters with large, red combs
______ as the trees in central and southeastern England became covered with dark pollutants, the dark
variety of the peppered moth became more abundant
______ Average-sized seeds become more common; the birds that eat the seeds become more specialized
with around the same (average) size beak length
______ Larger seeds become more common; the bird population evolves larger beaks
______ Average-sized seeds become less common and larger and smaller seeds become more common; the
bird population splits into 2 subgroups specializing in eating larger and smaller seeds.
______ Human infants have the best chance of surviving the trials of birth if they weigh between 7 and 8
pounds at birth; mortality is higher at higher or lower birth weights.
7. Explain each of the following and give an example of each:
a. Heterozygote advantage
b. Frequency-dependent selection
c. Sexual dimorphism
d. Intrasexual selection
e. Intersexual selection
8. Explain why evolution can never create a perfect organism.
Hardy-Weinberg Practice Problems
1. If a population has the following genotype frequencies, AA = 0.42, Aa = 0.46, and aa = 0.12, what are the
allele frequencies? Show your work and circle your answer.
2. In a population with two alleles, B and b, the allele frequency of B is 0.8. What would be the frequency
of heterozygotes if the population is in Hardy-Weinberg equilibrium? Show your work and circle your
answer.
3. In a population that is in Hardy-Weinberg equilibrium, 16% of the population shows a recessive trait.
What percent show the dominant trait? Show your work and circle your answer.
4. A Pangorian trait which results from simple Mendelian inheritance is antenna shape. Corkscrew
antennae (A) are dominant over straight antennae (a). When the entire Pangorian population was
screened (all 9,904 of them), 3,565 had corkscrew, while the rest had straight antennae.
a. What is the frequency of each allele? Show your work and circle your answers.
b. What percentage of the population has each of the genotypes? Show your work and circle your
answers.
c.
How many Pangorians are heterozygous for antennae shape? Show your work and circle your
answer.
d. The great ruler of Pangoria has determined that Pangorians born with straight antennae have a
greater tendency toward violent behavior than do those with corkscrew antennae. He also had
determined that neutering stops the violent behavior. He decrees that all Pangorians born with
straight antennae shall be neutered shortly after birth. In general, what will happen to the allele
frequencies in the population over the next six generations?
5. You collect 100 samples from a large butterfly population. Fifty specimens are dark brown, 20 are
speckled, and 30 are white. Coloration in this species of butterfly is controlled by one gene locus: BB
individuals are brown, Bb are speckled, and bb are white. What are the allele frequencies for the
coloration gene in this population? Show your work and circle your answers.
Is this population in Hardy-Weinberg equilibrium? Explain your answer.
6. A recessive mutation causes short sightedness (ss) in cats. The frequency of homozygous wild type
(+/+), heterozygous (+/s) and homozygous recessive (ss/ss) individuals was assessed in two populations
of cats. The data is shown in the chart below.
+/+
+/ss
ss/ss
Cat Population
Country cats
0.49
0.42
0.09
City cats
0.52
0.45
0.03
a. Are the two populations in Hardy-Weinberg equilibrium? Explain.
b. If one population is not, what might cause this deviation?
7. Another classification of blood group antigens is known as MN. Individuals are either homozygous for
M (MM) or N (NN), or they express both antigens (MN). You are studying the distribution of alleles in
a population of people. You determine that 90 people are MM, 60 are MN, and 50 are NN. Assign
symbols for the allelic frequency of the M and N alleles in the population. Determine the frequency of
each allele. Based on the allelic frequencies, determine (out of 200 individuals) the number of
individuals in the population that are expected for each genotype. Test, by chi square, whether the
population is in Hardy-Weinberg equilibrium. Show your work and circle your answer.
8. For an X-linked recessive trait, 9% of the females in the population are affected. What percent of the
males would be affected? What percentage of the population is represented by carriers? Show your
work and circle your answers.
9. You have been commissioned to study the genetic make-up of an ancient tribe of Arabs whose
descendents live in northern Saudi Arabia. They hire you to test for the frequencies of a number of wellknown genetic traits. The only hitch is that these people won’t let any outsiders go near the women.
“No problem” you say, “as long as I can test the men to determine the allele frequencies, I can figure out
the gene frequencies in women. That is, if the mode of inheritance is known, and if we can assume
Hardy-Weinberg equilibrium.” Prove you can by completing the following chart.
Trait
Mode of
Inheritance
Frequency of
trait in males
PTC
taster
Autosomal
dominant
0.75
Blue eyes
Autosomal
recessive
0.09
Color
blindness
X-recessive
0.05
Xg blood
type
X-dominant
0.40
Pattern
baldness
Autosomal
dominant in
males, recessive
in females
0.36
p
q
Frequency of
trait in females