10 Microevolution To Speciation

Question 1

Problems with Darwin’s model of natural selection (3)

Answer 1

Natural selection —> if variation exists in populions, some of this variation is heritable and some variants survive better than others. Leads to next generation of population being biased to variants. Over many generations - adaptation made.

Natural selection should drive any beneficial mutation to fixation

Process gets rid of genetic variation

Question 2

Blending inheritance destroys variation that exists

Answer 2

Natural selection required variation but blending inheritance gets rid of it - as does the process of natural selection

Question 3

Adding in mutations and heredity (2)

Answer 3

Mutation generates variation, permits novelty

Diploidy, segregation maintains variation in absence of selection

Question 4

Types of mutation

Answer 4

Silent mutations / Missense mutations / Nonsense mutations

Exon mutations may affect protein sequence and functions OR protein presence

Question 5

Mutations that effect transcription factors

Answer 5

Repressor - silencing element (prevents transcription)

Activator - enhancer elecmet (activated transcription)

Mutations in repressor / promoter / activator regions affect temporal and spatial patterns of gene expression

Question 6

What mutation events have large effects

Answer 6

Gene duplication / novel genes / endosymbiosis / changes in karyotype / polyploidy

Question 7

Does eveolution use small or large effect mutations?

Answer 7

Most selection on mutations of small effects allow for gradual and slow change overtime

Question 8

Why are macro mutations important in microbes

Answer 8

Analysis in microbial genomes —> widespread transfer of genetic material between microbes —> ‘cassettes’ of genes introduces = complete function transferred

Question 9

Macro mutations in eukaryotes

Answer 9

Symbiosis —> eukaryotes and photosynthetic eukaryotes —> genome duplication (Hox gene complexity and jawed fish)

Question 10

Influence of population size on mutations and adaptation

Answer 10

Smaller population size —> mutations less likely to happen —> slower adaptation rate

Mutation occurs in 1/1billion individuals / generation

Question 11

Selection acts on phenotype, underpinned by genotypes (simple)

Answer 11

Simple genetic basis —> underpinned by genes of 1 or few loci (can measure frequnecy directly / segregation patterns known / can use maths to model changes and track allelic variants)

Question 12

Selection acts on phenotype, underpinned by genotypes (complex)

Answer 12

Complex genetic basis —> underpinned by variation at many loci (quantitative traits / cant track individual loci / can track overall phenotype change using heritability)

Question 13

CALCULATIONS ON LECTURE VIDEO

Answer 13

X

Question 14

Quantitative traits, many aspects of phenotype are the sum…

Answer 14

Of many genetic loci (model evolution using heritability)

Question 15

Which allele can be selected for when rare

Answer 15

Dominant

Question 16

Paradox of genetic diversity - Natural selection should (2)

Answer 16

Drive any beneficial mutation to fixation (positive selection)

Drive any deleterious mutation out of population (purifying selection)

In theory these should get rid of genetic variation

Question 17

Deleterious variants

Answer 17

Selected against (subject to purifying selection - should be removed)

Question 18

Neutral variants

Answer 18

Doesn’t affect fitness (not subject to purifying selection)

Question 19

Advantageous variants

Answer 19

Selected for (subject to positive selection)

Question 20

Why does genetic disease persist

Answer 20

On average each person carries 4 lethal/deleterious mutations but vast majority are recessive so have little phenotypic effect unless homozygous and most individuals have different lethal mutations so each genetic disease is rare

Alleles causing genetic disease present because mutation is recurrent. Selection removed them, but does so slowly when rare (recessive). Therefore there are many different lethal mutations, all rare —> founder effects make particular genetic disease more common.

Question 21

Neutral mutations not subject to selection - why more diversity in large populations?

Answer 21

Neutral mutations don’t affect phenotype - outsider of genie regions (in introns) / third base pair positions so no AA change or affect phenotype in insignificant way - AA with same property coded for

Process of genetic drift - every neutral mutation has a chance of spreading into the population
Eventually every mutation will fix or be lost (but can hang around for a long time in large populations - fixed faster in smaller populations)

Question 22

Why is there still genetic diversity in naturally selected traits?

Answer 22

Classic model of natural selection - beneficial mutation (positive selection) mutation increases in frequency and everyone has it in the end

Question 23

Balanced polymorphism

Answer 23

Segregational variation - heterozygous advantage

Example - sickle cell anaemia (West Africa) - have oxygen carrying blood and resistant to malaria

Question 24

Environmental variation with gene flow

Answer 24

Spatially diversgant selection —> Point mutation (lactase persistence)

Mutations onlu spread in human populations where cattle domesticated, lack of fixation in these population: incoming genes / presence in other populations: move,net out of pastoralist societies

Question 25

Frequency dependant selection

Answer 25

Some traits are good when theyre rare - eg. Predators learn to detect common prey

Question 26

Processes that maintain adaptive genetic diversity (6)

Answer 26

1. Natural selection
2. Gene flow
3. Mutation
4. Genetic drift
5. Sexual selection
6. Balancing selection

Question 27

Natural selection

Answer 27

Favors traits that enhance survival and reproduction. It can maintain genetic diversity if different alleles are advantageous in different environments or circumstances

Question 28

Gene flow

Answer 28

Movement of alleles between populations. It can introduce new genetic variation or maintain diversity by preventing populations from becoming too genetically similar

Question 29

Mutation

Answer 29

Source of new genetic variation. Although mutations are generally rare, they provide new alleles that could be advantageous under certain environmental conditions

Question 30

Genetic drift

Answer 30

Random changes in allele frequencies, especially in small populations. Though it can reduce diversity, it can also play a role in maintaining unique alleles in isolated populations

Question 31

Sexual selection

Answer 31

Selection based on traits related to mate choice, which may maintain diversity in traits like coloration or display behaviors

Question 32

Balancing selection

Answer 32

A type of natural selection that maintains multiple alleles at a locus within a population (e.g., through heterozygote advantage or frequency-dependent selection)

Question 33

Red Queen Processes definition

Answer 33

Evolutionary processes where species must continuously adapt to survive against co-evolving organisms

These processes maintain genetic diversity by favoring adaptations that keep pace with changing environmental or biotic factors, such as the evolution of pathogens or predators

Question 34

Balanced Polymorphism definition

Answer 34

The maintenance of two or more alleles at a locus in a population at stable frequencies due to selective forces that maintain the diversity (e.g., heterozygote advantage or frequency-dependent selection)

Question 35

Environmental Heterogeneity definition

Answer 35

Variability in environmental conditions across space or time. It can maintain genetic diversity by favoring different alleles in different environments

Eg. one allele may be advantageous in one environment, while another allele may be advantageous in a different environment.

Question 36

Heterozygote Advantage definition

Answer 36

Form of balancing selection where individuals with two different alleles at a particular locus (heterozygotes) have a higher fitness than individuals with two identical alleles (homozygotes)

Can maintain genetic diversity at that locus

Question 37

Frequency-Dependent Selection definition

Answer 37

A type of selection where the fitness of a phenotype depends on its frequency relative to other phenotypes in the population.

For example, rare phenotypes may be more advantageous because predators or competitors focus on more common phenotypes, which maintains genetic diversity.

Question 38

Case study analysis - Red Queens

Answer 38

Co-evolution between host and parasite (eg. pathogens)

Question 39

Case study analysis - environmental heterogeneity

Answer 39

Different alleles are favored in varying environments (eg. Drought vs flood tolerance in plants)

Question 40

Case study analysis - heterozygous advantage

Answer 40

Sickle cell trait providing malaria resistance

Question 41

Case study analysis - frequency-dependant selection

Answer 41

Rare traits have higher fitness due to predator avoidance (eg. guppy coloration)