Mechanisms - Genetic Theory of Evolution

Question 1

Evolution

Answer 1

This is a two-step process: the origin of genetic variation by mutaiton/recombination followed by changes in frequencies of alleles and genotypes, caused by genoetype drift or natural selection.

Question 2

What is required of a feature to evolve by natural selection?

Answer 2

Must affect reproduction or survival

Question 3

How does NS differ from genetic drift, inbreeding and gene flow?

Answer 3

These three act at the same rate on all loci in the geome, NS proceed independetly at different loci

Question 4

Mosaic Evolution

Answer 4

This is a concept in palaeontology where evolutionary changes take place in some body parts or systems without simultaneous changes in other parts

Question 5

What are the three types of Natural Selection?

Answer 5

Directional
Stabilizing
Diversifying

Question 6

Directional Selection

Answer 6

This occurs when individuals homozygous for one allele havea fitness greater than that of individuals with other genotypes and indivduals homozygous for the other allele have a fitness less than that of indivdiuals with other genotypes.

Question 7

What is an example of directional selection?

Answer 7

If a commmonly varying trait like size, directional selection would occur if phenotype for greater than the mean average had higher fitness that the mean phenotype.

Question 8

Stabilizing Selection

Answer 8

This is if the mean phenotype in the population has highest fitness

Question 9

What does stabilizing selection favour?

Answer 9

Intermediates thus variation is reduced in the populations

Question 10

How is stabilziing selection represented?

Answer 10

Hardy-Weinberg Equilibrium

Question 11

Hardy-Weinberg Equilibirum

Answer 11

This describes how allele frequencies in a population will remain constant from generation to generation in the absence of other evolutioanry forces

Question 12

What is the HW equation?

Answer 12

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

Question 13

Derive the HW equation?

Answer 13

p and q are frequences of two allele for a gene, the other three being frequencies of the genotypes for that gene (AA, Aa and aa)

Question 14

Why does allele frequency stay the same in stabilizing selection?

Answer 14

p and q are equal, the heterozygote higher than either AA or aa

Question 15

What is an example of stabilizing selection?

Answer 15

Human babies with a bimodal distribution favouring intermediate birth weights.

Question 16

What is Overdominance in directional selection?

Answer 16

Heterozygote advantage is a type of natural selection occuring when the heterozygote has higher fitness that either homozygote.

Question 17

Diversifying Selection

Answer 17

This is if two or more phenotypes are fitter than the intermediates between them, that meaning indivdiuals both ends of the trait distribution are favoured.

Question 18

What is an example of diversifying selection?

Answer 18

If phenotyp selected was large size, A1A1 would be fittest if largest, but A1A2 favoured if larger than either homozygote.

Question 19

What consequences does Diversifying selection have on the population?

Answer 19

If homozygote was largest, population would become fixed for that allele, but not if the heterozygote was largest.

Question 20

Fitness

Answer 20

Average per capita lifetime contribution of indivdiuals of that genotype to the population after one or more generations.

Question 21

Reproductive Success

Answer 21

This is the average number of eggs or offspring one generation, acounting also for those who survive to reproduce.

Question 22

How can reproductive success be conceptualized?

Answer 22

Aseuxal populations: a population of only parthenogenetic females with proportion of eggs of genotype A that survive to reproductive age is 0.05 in a batch of 60 eggs, then fitness of A is calculated by proportion surviving x average fecundity or 0.05x60=3

Question 23

What would a Reproductive Success of 3 mean?

Answer 23

Genotype grows by 3 per generation

Question 24

Relative FItness

Answer 24

This describes per capita growth rate of R relative to a reference genotype(usually assigned a relative fitness of 1)

Question 25

Mean Fitnesss

Answer 25

Average fitness of indivdiuls in a population relative to the fittest genotype

Question 26

Coefficient of Selection

Answer 26

This is the amount by which the fitness of a genotype differs from the reference genotype.

Question 27

What is the COS used for?

Answer 27

Quantify strength of selection acting on a particular genotype, taking GF change by NS independent of other evolutionary processes.

Question 28

What does ROS measure?

Answer 28

Advantage of the fittest genotype and intensity of selection against the least fittest a=0.75 and b=0.25

Question 29

How is ROS more complex in sexually reproducing organisms?

Answer 29

Two males have differing fitness

Question 30

How is ROS measured in sexual reproduction?

Answer 30

Intervals of time as this is dependent on organisms reaching a particular age class and fecundity of that age class.

Question 31

What is measurement of intervals of time influenced heavily by?

Answer 31

Age at which females have offspring (if A reproduces at 6 months and B at 12 months)

Question 32

What do GF depend on in SP?

Answer 32

Allele frequencies among uniting gametes by haploid gamete transmission.

Question 33

What is natural selection dependent on?

Answer 33

How allele frequency changes are determined by the components of fitness of each zygotic and each gametic genotype.

Question 34

When does adaptive evolution occur?

Answer 34

When the homozygote for an advantageous allele has a fitness equal to or higher than the heterozygote or any other genotype in a population

Question 35

When does an advantageous allele become prominent?

Answer 35

Selectively neutral previously or retained by balancing selection

Question 36

Why is an allele unlikely to become fixated if initally rare?

Answer 36

An allele increasing from a low frequency invade a population.

Question 37

Aposematism

Answer 37

This is the use of warning coloration to inform potential predators that an animal is poisonous, venomous or otherwise dangerous.

Question 38

When is a locus under directional selection best observed?

Answer 38

Recently altered environments.

Question 39

What is an example of directional selection?

Answer 39

Brown rats in Warfarin resistance, inhibiting enzyme responsible for Vit K regeneration

Question 40

What is the process of Warfarin resistance?

Answer 40

Resistant rats exposed to warfarin have higher survival advantage, thus frequency of mutation increase near to 1, whilst resistant rats disadvantages in VitK deficiencies compared to susceptible rats.

Question 41

How can deleterious allele persist?

Answer 41

Reintroduction by recurrent mutation or gene flow from other populations in whic they are favoured

Question 42

What is deleterious allele persistance balanced by?

Answer 42

Rate it is eliminated by selection and rate it is introduced

Question 43

What is equilibirium frequency of a deleterious recessive allele proporitonal to?

Answer 43

Mutaiton rate and inversely proportional to strength of selection

Question 44

Incomplete Dominance

Answer 44

This is when the heterozygote having one copy of wild-type and deleterious allele, has intermediary phenotypes between homozygous wild type/mutant.

Question 45

Wright-Fisher Model equation…

Answer 45

p(t+a) = p(t)(1-s).p(t)(1-s)+(1-p(t))

Question 46

What is an example of deleterious allele frequency fixation?

Answer 46

Sickle Cell Anemia where the heterozygote are resistant to malaria.