Chapter 23: The evolution of populations (2)

Question 1

What is the Hardy-Weinberg principle used for?

Answer 1

The Hardy-Weinberg equation describes the genetic makeup we expect for a population that is not evolving at a particular locus.

Question 2

How to calculate the number of copies of each allele?

Answer 2

• 320 red flowers (CRCR)
  – 160 pink flowers (CRCW)
  – 20 white flowers (CWCW)
• Calculate the number of copies of
  each allele:
  – CR = (320 x 2) + 160 = 800
  – CW = (20 x 2) + 160 = 200

Question 3

How to calculate the frequency of each allele?

Answer 3

• To calculate the frequency of each allele:
  – p = freq CR = 800 / (800 + 200) + 0.8
  – q = freq CW = 200 / (800 + 200) + 0.2

Question 4

What is the Hardy-Weinberg equilibrium?

Answer 4

In a population that is not evolving, allele and genotype frequencies will remain constant from generation to generation,
provided that only Mendelian segregation and recombination of alleles are at work.

Question 5

What is the Hardy- Weinberg equation?

Answer 5

If p and q represent relative frequencies of only two possible alleles in a population at a particular locus, then
– p square + 2pq + q square = 1

Question 6

What are the conditions required for Hardy-Weinberg equilibrium?

Answer 6

1. No mutations
2. Random mating
3. No natural selection
4. Extremely large population size
5. No gene flow

Question 7

Natural populations cannot evolve at some loci while being in Hardy-Weinberg equilibrium at other loci. True or false?

Answer 7

False. Natural populations can evolve at some loci, while being in Hardy-Weinberg equilibrium at other loci.

Question 8

What can the Hardy-Weinberg equation be used for?

Answer 8

H-W equation can be used to estimate the percentage of a population carrying alleles for an inherited disease.

Question 9

Why do we assume that phenylketonuria is in Hardy-Weinberg equilibrium?

Answer 9

1. The PKU gene mutation rate is low
2. Mate selection is random to whether or not an individual is a carrier for the PKU allele
3. Natural selection can only act on rare homozygous individuals who do not follow dietary restrictions
4. The population is large
5. Migration has no effect as many other populations have similar allele frequencies

Question 10

What are the 3 major factors alter allele frequencies and bring about most evolutionary change?

Answer 10

– Natural selection
– Genetic drift
– Gene flow

Question 11

What is adaptive evolution?

Answer 11

By consistently favoring some alleles over others, natural selection can cause adaptive evolution, a process in which traits that enhance survival or reproduction tend to increase in frequency over time.

Question 12

Certain circumstances can result in genetic drift having a significant impact on a population. What are 2 examples of this?

Answer 12

Founder effect and bottleneck effect.

Question 13

Define founder effect.

Answer 13

When a few individuals become isolated from a larger population, this smaller group may establish a new population whose gene pool differs from the source population; this is called the founder effect

Question 14

Define bottleneck effect.

Answer 14

A sudden change in the environment, such as a fire or flood, may drastically reduce the size of a population.

A severe drop in population size can cause the bottleneck effect, so named because the population has passed through a “bottleneck” that reduces its size

Question 15

The _________ probably accounts for the relatively high frequency of certain inherited disorders among isolated
human populations.

Answer 15

The founder effect probably accounts for the relatively high frequency of certain inherited disorders among isolated
human populations.

Question 16

What are the effects of genetic drift?

Answer 16

1. Genetic drift is significant in small populations.
2. Genetic drift can cause allele frequencies to change at random.
3. Genetic drift can lead to a loss of genetic variation within populations.
4. Genetic drift can cause harmful alleles to become fixed

Question 17

Define gene flow.

Answer 17

Allele frequencies can also change by gene flow, the transfer of alleles into or out of a
population due to the movement of fertile individuals or their gametes

Question 18

What are the different ways natural selection differs in terms of the phenotypes preferred?

Answer 18

Directional selection, disruptive selection, and stabilizing selection.

Question 19

Define directional selection.

Answer 19

Directional selection occurs when conditions favor individuals exhibiting one extreme of a phenotypic range.

Question 20

Define disruptive selection.

Answer 20

Disruptive selection occurs when conditions favor individuals at both extremes of a phenotypic range over intermediate phenotypes.

Question 21

Define stabilizing selection.

Answer 21

Stabilizing selection acts against both extreme phenotypes and favors intermediate variants.