Lecture 20 Flashcards Preview

Genetics > Lecture 20 > Flashcards

Flashcards in Lecture 20 Deck (55):

The change in gene freq over time in a population - which leads to speciation and divergence.



How is the reproductive success of an organism measured?

- Number of offspring
- Quality/probably fitness of offspring


Why is variation important for species survival?

- Variation by mutations is the basis of natural selection/evolution

- Organisms whose variation increase their fitness will adapt, survive and mate, passing these selected traits on


A group of interbreeding, sexually reproducing individuals sharing a common set of genes.



Frequencies affected by evolutionary forces: mutation, gene flow, genetic drift, and natural selection

Genetic variation


Bighorn sheep suffered from loss of genetic variation due to genetic drift or founder effect due to a founding population of only 12 indiv in 1922. What saved bighorn sheep?

Adding new genetic variation by introducing sheep from other populations

Rams with lots of migrant genes were > 2x more successful at producing healthy young than those with less genetic diversity


Equation for calculating genotypic freq

Number of indiv possessing phenotype/total number of alleles

f(AA) = #AA indiv / N


Equation for calculating allelic freq (freq of an allele)

Number copies of a particular allele/total number of alleles in a population


Hardy-Weinberg Equilibrium

Allele and gene polypeptide freq in a popul will remain constant from generation to generation in the absence of other evolutionary influences.


Hardy-Weinberg Equilibrium assumptions

1. Large popul
2. Random mating
3. No mutations
4. No migration
5. No natural selection


Does H-W equil ever occur naturally?



Look at lecture for practice calculating genotype and allele freq



When a population is in H-W equilibrium, the proportions of genotypes are determined by what?

The frequency of alleles


Positive assortative mating
Negative assortative mating

PAM - a tendency of like individuals to mate
NAM - a tendency of unlike individuals to mate



A measure of the probability that two alleles are identical by descent


Alleles identical by descent
Alleles identical by state

Descent - Alleles descended from the same copy in a common ancestor

State - Alleles that are the same in structure and function but are descended from two different copies in ancestors


What is Inbreeding depression and why does it occur?

Increased appearance of lethal or deleterious traits caused by inbreeding

Inbreeding increases percentage of homozygous individuals in the population


The avoidance of mating between related individuals



Is it possible to do H-W equations with traits inherited in ways other than typical 2 allele dominant/recessive mechanisms?

Yes, can do it with 3 and also X-linked alleles


The study of the distribution and change in frequency of alleles within populations.

Population Genetics


When would there be a change in heterozygote freq?

If homozygotes are more advantageous, thus heterozygotes would be selected against


Could the population ever reach a state with 0 heterozygotes?

Probably not unless speciation occurred.

If homozygotes only breeding with other homozygotes, eventually new species would branch off


What would increase the percentage of homozygotes in a population?

A. Outcrossing
B. Inbreeding
C. Self-ferlization
D. A and B
E. B and C
F. All of the above

E. Inbreeding and self-fertilization


Which would lead to a completely homozygous population?

A. Outcrossing
B. Inbreeding
C. Self-ferlization
D. A and B
E. B and C
F. All of the above

C. Self-fertilization


H-W equilibrium assumption(s) would be violated if there is inbreeding or self-fertilization. Which of the following are reasons why?

A. Small population
B. Non-random mating
C. Natural selection would now occur
D. Inbreeding can cause mutations in DNA
E. All of the above
F. A and B
G. A, B and C

F. A and B


What can occur as a consequence of inbreeding?

A. Increase in homozygotes
B. Non-viable offspring
C. Decrease in average yield of crop
D. Decrease in number of offspring
E. A, B, D
F. All of the above

F. All of the above


What is the effect of outcrossing on a population?

A. Allelic freq changes
B. There will be more heterozygotes than predicted by H-W law
C. There will be fewer heterozygotes than predicted by H-W law
D. Genotypic frequencies will equal those predicted by H-W law

A. Allelic freq changes


When are proportions of genotypes determined by frequency of alleles?

A. Inbreeding
B. Random mating
C. Back crossing
D. H-W equilibrium
E. B and D

D. H-W equilibrium


Which occurs in greatest freq when Allelic frequencies are equal (p=q=0.5)?

A. Heterozygote
B. Homozygous dominant
C. Homozygous recessive
D. None of the above

A. Heterozygotes


If incidence of cystic fibrosis is 1/2500 (0.0004), what proportion of people are carriers for CF?

q^2 = (0.0004)^2 = 0.02

1 = p-q ---> p = q-1 ---> p = 0.02-1 ---> p=0.98

2pq = 2(0.02)(0.98) = 0.04 or 1/25 are carriers for CF mutation



A. Natural selection
B. Nonrandom mating
C. Mutation
D. Migration
E. Genetic drift
F. Epigenetics
G. Gene flow

1. Permanent alteration in DNA seq that makes up a gene
2. Movement of populations, groups, or individuals
3. Heritable changes in phenotype that are not due to changes in DNA seq
4. Movement of genes from one population to another
5. Change in freq of a gene variant (allele) in a population due to random sampling of organisms
6. Differential survival and reproduction of indiv due to differences in phenotype
7. When probability that two indiv in a population will mate is not the same for all possible pairs of individuals

1. C.
2. D.
3. F.
4. G.
5. E.
6. A.
7. B.


What is it called when members of one biological sex choose mates of the other sex and compete with members of the same sex for access to members of the opposite sex?

Nonrandom mating - sexual selection


How did Nonrandom mating - sexual selection cause the extinction of Irish Elk?

Large antlers on males were preferred by females when choosing a mate. Antlers became so large, through reinforcing sexual selection, that bulls eventually could not carry on the normal business of life and so become extinct.


Forward and reverse mutations:

A. Can change allele frequencies
B. Can reach equilibrium
C. Do not change allele frequencies
D. Cannot reach equilibrium
E. A and B
F. C and D

E. A and B


When would forward and reverse mutations reach equilibrium?

When rate of forward mutations and rate of reverse mutations are equal and remain constant


How do rates of forward and reverse mutations eventually occur at same rate?

More gene 1
More forward mutations
Increase in freq of gene 2
Increase in number of alleles undergoing reverse mutation
Equilibrium - forward and reverse mutations at same rate


What happens to change in recurrent mutation as frequency of mutating allele drops?

A. Speeds up
B. Remains constant
C. Slows
D. None of the above

C. Slows


T/F: Influx of genes from an outside population cannot dramatically change allele freq.

False, Influx of genes from an outside population CAN dramatically change allele freq


What does the amount of change in Allelic freq due to migration btw populations depend on?

A. Difference in Allelic freq
B. Extent of migration
C. Inbreeding
D. A and B
E. All of the above

D. A and B


What is characterized as Variation in relative freq of different genotypes in a small population, owing to the chance disappearance of particular genes as indiv die or do not reproduce?

A. Genetic drift
B. Gene flow
C. Divergence
D. All of the above

A. Genetic drift


Two main causes of genetic drift

Founder effect
Genetic bottleneck


What is the sharp reduction in size of a population due to environmental events (natural disasters) or human activities (genocide)

Genetic bottleneck


What is characterized as reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors?

Founder effect


What can cause Allelic frequencies of populations to diverge and become fixed for one allele or the other?

A. Increasing genetic diversity
B. Inbreeding depression
C. Migration
D. Genetic drift

D. Genetic drift


What is defined as the relative reproductive success of a genotype compared to other genotypes in the population?



How do you I calculate fitness?

(# of offspring produced) / (mean # of offspring produced by most prolific phenotype)


1. Type of selection in which one allele or trait is favored over another

2. Relative intensity of selection against a phenotype

1. Directional selection
2. Selection coefficient


When can evolution through natural selection occur remarkably quickly?

A. Strong selection pressure
B. Self-fertilization
C. Rapid reproductive rates
D. Small population
E. B and D
F. A and C
G. All of the above

F. A and C


Overdominance vs Underdominance

Overdominance - Heterozygotes favored over homozygotes and have a reproductive advantage which maintains both alleles in a population (Heterozygote advantage)

Underdominance - Heterozygote has a lower fitness than both homozygotes (homozygotes advantage)


Which leads to unstable equilibrium?

A. Over dominance
B. Selection
C. Under dominance
D. All of the above

C. Under dominance


Matching: Choose two letters for each statement. One letter will define statement and the other letter will cause the statement to occur.

1. Extreme values for a trait are favored over intermediate values. Population divided into two distinct groups.

2. Extreme phenotype is favored over other phenotype. Allele freq will shift over time in direction of that phenotype.

3. Genetic diversity decreases and the population mean stabilizes on a particular phenotype. In this type of selection the intermediate phenotype is favored over extreme phenotypes

A. Stabilizing selection
B. Disruptive selection
C. Directional selection
D. Under dominance
E. Overdominance

1. B, D
2. C, D
3. A, E


Comment on how being heterozygous for sickle cell anemia is reproductively advantageous in regions with high levels of malaria

Homo dominant (normal) - die of malaria; no sickle cell anemia
Homo rec - die of sickle cell anemia; Less susceptible to malaria
Hetero carriers - No sickle cell anemia; Less susceptible to malaria

In malaria infected cells of heterozygotes, the O2 level is lowered enough to cause sickling which kills cell and destroys parasite


1. The frequency of a recessive allele at equilibrium is equal to:

2. The frequency of a dominant allele at equilibrium is equal to:

1. The frequency of a recessive allele at equilibrium is equal to the square root of the mutation rate divided by the selection coefficient

2. The frequency of a dominant allele at equilibrium is equal to mutation rate divided by the selection coefficient


Short and long term effects of:

1. Mutation
2. Migration
3. Genetic drift
4. Natural selection

1. Short - Change in Allelic freq; Long - Equil reached btw forward and reverse mutations
2. Short - Change in Allelic freq; Long - Equil reached when Allelic freq of source and recipient popul are equal
3. Short - Change in Allelic freq; Long - Fixation of one allele
4. Short - Change in Allelic freq; Long - Directional selection: fixation of one allele, Overdominant (stabilizing) selection: Equil reached


The average number of offspring produced by three genotypes are: GG = 6; Gg = 3; gg = 2. What is the fitness of Gg?

A. 3
B. 0.5
C. 0.3
D. 0.27

B. 0.5

(Avg offspring of Gg) / (Avg offspring of most prolific genotype - GG)

3/6 = 0.5