Theme 4B/C: Population Genetics and the Ways of Change

Question 1

What is a population?

Answer 1

• An interbreeding group of individuals that belong to the same species and live within a restricted geographical area.

Question 2

What’s the null hypothesis for evolution?

Answer 2

• There will be no change in allele frequencies over time within a population.

Question 3

What impact does random mating have on a population?

Answer 3

• Even if a population is not in Hardy-Weinberg Equilibrium, one round of random mating with the other conditions met will return the population to equilibrium

Question 4

What is genetic drift?

Answer 4

• Random processes that can change the frequencies of genetic variants and traits during life cycles, especially mating and survival
• Has very big implications on smaller populations

Question 5

What’s one of the major impacts of genetic drift?

Answer 5

• Impacts heterozygosity!

Question 6

What’s a bottleneck?

Answer 6

• A type of genetic drift. Temporary reductions in population size cause drift, reduce genetic variation, and cause genetic differences between populations
• Reductions can be caused by natural disasters, such as forest fires
• Has major conservation implications

Question 7

What’s Founder’s Effect?

Answer 7

• A type of genetic drift where new populations are started by a small number of individuals (think of the Amish)
• Often causes a decline in genetic diversity

Question 8

What are some things found in common between bottlenecks and the Founder’s Effect?

Answer 8

• Both methods lead to population divergence
• Causes allele frequencies to randomly change
• Often causes reductions in genetic variation

Question 9

What are the three forms of non-random mating?

Answer 9

• Inbreeding - Mating with relations
• Outbreeding - mating with individuals more distantly related
• Assortative mating - Individuals with similar genotypes and/or phenotypes mate with one another more frequently then would be expected under a random mating pattern

Question 10

How does inbreeding occur? What are its consequences?

Answer 10

• Caused by small populations and certain mating systems (absolute, geographic or cultural)
• Alters genotype frequencies, but does not alter allele frequencies by itself
• Causes a decrease in heterozygosity and results in reduced fitness since rare and deleterious alleles are more likely to combine

Question 11

What conditions make evolution by Natural Selection inevitable?

Answer 11

• Individuals vary
• Survival and reproduction are not random
• Variation is passed on to offspring

Question 12

What’s directional selection?

Answer 12

• Individuals of one extreme phenotype are favoured in the population
• Shifts the trait mean to one extreme
• Ex. the peppered-moth

Question 13

What’s stabilizing selection?

Answer 13

• Individuals with intermediate phenotype favoured (i.e., the heterozygotes), extreme phenotypes are selected against
• Also known as balancing election
• Variance decreases between generations but the trait mean does not change
• Average individuals have higher fitness than extreme phenotypes
• Ex. heterozygotes with Sickle Cell Anemia

Question 14

What’s disruptive selection?

Answer 14

• Both extreme phenotypes favoured, intermediate phenotypes selected against
• Average individuals have lower fitness than extreme phenotypes
• Ex. dark and light-coloured oysters in their ability to camouflage.

Question 15

In what categories does selection manifest?

Answer 15

• Viability selection - differences in survival
• Fecundity selection - differences in reproductive success

Question 16

What’s sexual monomorphism?

Answer 16

• Male and female phenotypes are identical
• Swans, geese

Question 17

What’s sexual dimorphism?

Answer 17

• Male and female phenotypes are different
• Humans, peacocks

Question 18

What’s the goal of sexual selection?

Answer 18

• Not about driving towards perfection, often comes down to who can produce more offspring than the other guy

Question 19

What’s the difference between intrasexual selection and intersexual selection?

Answer 19

• Intrasexual selection - fitness differences resulting from differing abilities of the members of the same sex to compete for mating opportunities (ex. male polar bears fighting for mates)
• Intersexual selection - fitness differences resulting from preferential mating between specific males and females (ex. female peacocks choosing males with the brightest plumage)

Question 20

What are the different limitations placed on females and males reproductive success?

Answer 20

• Females are limited by resources
• Males are limited by access to females (usually the case)

Question 21

What drives population divergence?

Answer 21

• Driven by natural selection or drift between environments

Question 22

What are the four factors that cause genetic divergence?

Answer 22

• Genetic drift
• Founder effect
• Mutation
• Differential selection (which parents will mate to produce offspring)

Question 23

What are some of the prezygotic barriers that can lead to reproductive isolation?

Answer 23

• Habitat isolation - Species may prefer to mate in different geographical areas
• Behavioural isolation - Methods used to attract mates may differ
• Temporal isolation - Timing when species are reproductively active may differ
• Mechanical isolation - some species are physically unable to mate
• Genetic isolation - zygotes are unable to form due to very different gametes

Question 24

What are some of the postzygotic barriers that can lead to reproductive isolation?

Answer 24

• Reduced hybrid viability - hybrid will not be healthy and is born with defects. Individual not adapted well to either parents’ environments
• Reduced hybrid fertility - hybrid may not produce babies/offspring. May be caused by the number of chromosomes
• Hybrid breakdown - Reproductive failure of hybrid, genetic traits are not passed on

Question 25

What’s allopatric speciation?

Answer 25

• A physical barrier divides a geographic range, dividing the population for a long period of time
• Gene flow ceases and separate populations evolve independently.
• Over time, different alleles may become fixed
• Populations, when reintroduced, may be unable to reproduce. This is when speciation occurs.

Question 26

What’s sympatric speciation?

Answer 26

• There’s no geographic barrier, but instead, behavioural barriers that stop gene flow
• A form of disruptive selection that favours the extreme phenotypes to the point where they may not even recognize one another
• Ex. the stickle back fish

Question 27

What’s autopolyploidization?

Answer 27

• A rare case when polyploidy can lead to speciation
• Meiosis fails and the organism produces 2n gametes
• If 2n gamete is fertilized with another 2n gamete, an autopolyploid is created, often very large in size
• Autopolyploids can only mate with other polyploids

Question 28

What’s the morphological species concept?

Answer 28

• A very traditional concept of organizing species by their discrete physical characteristics
• Advantages in that it’s practical and easy to use, but not very reliable

Question 29

What’s the biological species concept?

Answer 29

• Groups species as groups of actual or potentially interbreeding natural populations that are reproductively isolated from other such groups
• Thought to be the most useful method