2.2a Drift and selection

Question 1

What is evolution?

Answer 1

the change over time in proportion of individuals in a population differing in one or more inherited traits

Question 2

What happens during evolution?

Answer 2

changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift

Question 3

What does variation in traits arise from?

Answer 3

mutations

Question 4

What is a mutation?

Answer 4

the original source of new sequences of DNA

Question 5

Explain mutations

Answer 5

• these new sequences can be novel alleles
• most mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual

Question 6

How much do populations produce?

Answer 6

more than the environment can support

Question 7

How does natural selection work?

Answer 7

Individuals with variations that are better suited to their environment tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation

Question 8

What does selection result in?

Answer 8

non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.

Question 9

What is sexual selection?

Answer 9

the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring

Question 10

What may sexual selection lead to?

Answer 10

sexual dimorphism

Question 11

What can sexual selection be due to?

Answer 11

• male-male rivalry
• female choice

Question 12

What is male-male rivalry?

Answer 12

• large size or weaponry
  increases access to females through conflict.

Question 13

What is female choice?

Answer 13

females assessing the fitness of males

Question 14

When does genetic drift occur?

Answer 14

when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next

Question 15

When is genetic drift more important and why?

Answer 15

• in small populations alleles are more likely to be lost from the gene pool

Question 16

When do population bottlenecks occur?

Answer 16

when a population size is reduced for at least one generation

Question 17

When does the founder effect occur?

Answer 17

through the isolation of a few members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool.

Question 18

How is the gene pool altered by genetic drift?

Answer 18

certain alleles may be underrepresented or over-represented and allele frequencies change

Question 19

What are selection pressures?

Answer 19

the environmental factors that influence which individuals in a population pass on their alleles.

Question 20

When happens when the selection pressures are strong?

Answer 20

the rate of evolution can be rapid

Question 21

What can selection pressures be and give examples?

Answer 21

• biotic
  
  • competition
  • predation
  • disease
  • parasitism
• abiotic
  
  • changes in temperature
  • light
  • humidity
  • pH
  • salinity

Question 22

What does the Hardy-Weinberg (HW) principle sate?

Answer 22

, in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the
generations

Question 23

What are the conditions for maintaining the Hardy Weinberg principle?

Answer 23

• no natural selection,
• random mating,
• no mutation,
• large population size
• no gene flow (through migration, in or
  out).

Question 24

What can the Hardy Weinberg principle be used for?

Answer 24

determine weather a change in allele frequency is occurring in a population over time

the HW principle to calculate allele,
genotype and phenotype frequencies in populations.

Question 25

What is the HW equation?

Answer 25

p^2+2pq+q^2=1

Question 26

What do each of the letters in the HW equilibrium represent?

Answer 26

p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant
genotype
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive
genotype