Genetic Variation (PP17)

Question 1

explain Quantitative characters:

Answer 1

vary along a continuum / spectrum within a population

Usually due to polygenic inheritance (additive effects of 2 or more genes influence single phenotypic character)

Question 2

explain Discrete characters:

Answer 2

generally an either-or

Usually determined by a single locus with different alleles with distinct impacts on the phenotype

Question 3

explain polymorphism

Answer 3

When 2 or more discrete characters are present & noticeable within a population

Question 4

polymorphism applies to what characters?

Answer 4

Applies only to discrete characters, not quantitative characters

Question 5

what are contrasting forms called?`

Answer 5

morphs

Question 6

give an example of morphs

Answer 6

Red-flowered & white-flowered morphs in a wildflower population, or butterflies

Question 7

are humans polymorphic

Answer 7

YES
Human populations are polymorphic for a variety of physical (e.g. freckles) & biochemical (e.g. blood types) characters

Question 8

what does gene diversity measure

Answer 8

Gene diversity: measures average % of gene loci that are heterozygous

Question 9

what does nucleotide diversity measure

Answer 9

Nucleotide diversity: measures the level of difference in nucleotide sequences (base pair differences) among individuals in a population

Question 10

what do population genecists measure

Answer 10

Population geneticists measure genetic variation both at the level of whole genes & at the molecular level of DNA

Question 11

do Humans have relatively little or a lot genetic variation compared to many other organisms

Answer 11

a little

Question 12

What equation shows Evolution of a population can be explained as changes in allelic frequencies over time

Answer 12

Hardy-Weinberg Equilibrium
If certain conditions are met, allelic (genotypic) frequencies will not change

Genetic frequencies will stabilise to certain proportion:
p2 2pq q2

Question 13

What conditions does the hardy-weinberg equilibrium need to met.

Answer 13

Large population
No mutation (no new alleles)
No migration (isolated)
No natural selection
No sexual selection (random mating)

Question 14

What happens when all conditions of hardy-weinberg met?

Answer 14

If all of these conditions are met, then we arrive at HW equilibrium:

Question 15

can a population be in HW equilibrium for 1 locus but not others?

Answer 15

yes

Question 16

what are genetic frequencies determined by?

Answer 16

Allelic frequencies

Question 17

LOOK AT SLIDES FOR HARDY WEINBERG EQUATION

Answer 17

LOOK AT SLIDES

Question 18

explain fitness

Answer 18

fitness = reproductive success of a genotype; generally we think of relative fitness (how well a certain genotype does compared to other genotypes in the same population)

Question 19

fitness equation

Answer 19

LOOK AT SLIDES

Question 20

What does the most prolific genotype mean and what fitness (W) does it have?

Answer 20

Most prolific genotype means the one that produces the most offspring

Most prolific genotype is considered to have fitness (W) of 1

Question 21

what are the two ways of genetic variation

Answer 21

Mutations

-allele resorting

Question 22

how do you get new alleles

Answer 22

due to changes in nucleotide bases

Question 23

true or false: Mutations are Continuous, spontaneous, unpredictable, but inducible

-ONly Mutations that are present in gametes will be passed on

Answer 23

true

true

Question 24

name the ways of allele resorting

Answer 24

• Sexual reproduction (two different parents)
• Segregation of alleles from different parents into different gametes
• Crossing-over
• Random fertilization

Question 25

explain macroevolution

Answer 25

Large-scale changes in organisms (obvious differences in traits) These changes are observable only after many generations

Question 26

explain microevolution

Answer 26

Generation-to-generation change in allele frequency in a population Generally fairly subtle changes

Question 27

what is one difference between macro and micro evolution and one similarity?

Answer 27

DIFFERENCE: Examination of the same process at different scales SIMILAR: Both are due to non-random selection of random variation

Question 28

what are the 4 definitions of a species

Answer 28

Biological Species Concept: Morphospecies Concept: Ecological Species Concept: Phylogenetic Species Concept:

Question 29

explain biological species concept and why would the definition not be true?

Answer 29

- Organisms considered to be of same species if they can produce viable & fertile offspring - because of two barriers: PostZygotic and PreZygotic

Question 30

Explain Prezygotic Barrier

Answer 30

Pre-zygotic: before a sperm and egg cell even get the chance to fuse “Causes for reproductive isolation"

Question 31

explain Post zygotic barrier

Answer 31

Post-zygotic: diploid cell is created, but fail to produce an organism that meets the definition of a species according to the above definition

Question 32

explain the morphospecies concept

Answer 32

Different species will look different - based on the morphology (physical characteristics)

Question 33

explain ecological species concept

Answer 33

Species defined based on role within ecosystem - each species will have a distinct role (“niche”)

Question 34

explain the phylogenetic species concept

Answer 34

Species determined by proximity / grouping on a phylogenetic tree - if grouped together, considered the same species.

Question 35

what are the prezygotic factors

Answer 35

Behavioural Isolation: 1 organism has a mating ritual that does not appeal to another (e.g. specific songs or “dances”) Mechanical Isolation: Reproductive organs of the 2 organisms do not properly interact to allow fertilization Temporal Isolation: 2 organisms are not active at the same time of day (e.g. nocturnal vs. diurnal) Habitat / Ecological Isolation: 2 organisms live in different habitats / regions & so do not have exposure to one another Gametic Isolation: Gametes of the organisms fail to fuse to form a zygote (usually due to differences in # chromosomes)

Question 36

what are the post zygotic factors (ie. why they can reproduce)

Answer 36

Reduced Hybrid Viability: Hybrid is not as physically fit as either parents (has a higher risk of disease or malformations, or is mal-adapted) Reduced Hybrid Fertility: Hybrid is sterile & cannot pass on its genes (e.g. mules) Hybrid Breakdown: F1 hybrid generation is viable & fertile but the F2 generation shows decreased viability & fertility

Question 37

what are the two types of speciation

Answer 37

Allopatric speciation | Sympatric speciation

Question 38

explain allopatric speciation

Answer 38

Due to geographical barrier that splits apart population of a common species Create reproductive barrier that causes both populations to adapt differently After many, many generations, this will ultimately lead to the differentiation of two distinct species that cannot interbreed e.g. continental drift, highways

Question 39

explain sympatric speciation

Answer 39

Sympatric speciation: Any speciation not due to geographical barrier Some other event / series of events causes a divergence e.g. disruptive selection (if open a new niche, mate discrimination)

Question 40

What are the 5 factors that determine Allele frequencies

Answer 40

``` Mutation Genetic Drift Gene Flow Sexual Selection Natural Selection ```

Question 41

explain genetic drift

Answer 41

Change in gene pool due to chance; result of random events / changes that cause allele frequencies to change Can end up getting rid of beneficial, harmful, or neutral alleles (because it’s chance) Can occur in small, unrepresentative populations Can lead to decreased genetic variation within a population (but increases differences between populations)

Question 42

what are the two important mechanisms in genetic drift

Answer 42

2 important mechanisms: Bottleneck effect Founder effect

Question 43

explain the bottleneck effect | SEE DIAGRAM IN SLIDES

Answer 43

Occurs when an event causes only a small fraction of a population to survive (catastrophe, disease, food shortage, habitat loss, etc.) Since population is small, it’s possible (nay, likely) that there’s imbalanced representation of alleles from the original population Less-frequent alleles may no longer exist (if no carriers present in new population)

Question 44

give examples of bottle neck effect

Answer 44

insect survival through the winter, at-risk/endangered species (Florida Panther)

Question 45

explain the founder effect

Answer 45

Occurs when very few individuals from larger population establish a new colony Bring only small sample of original genetic diversity New population has only the alleles brought by the founders (less diverse than original population)

Question 46

give example of founder effect

Answer 46

Prevalence of Huntington’s disease amongst Afrikaners (South Africa) due to presence of disease in small population of Dutch settlers

Question 47

explain gene flow

Answer 47

Exchange of alleles due to migration between populations Interactions within metapopulation Reduce differences between populations that might have arisen through genetic drift / selection Can transfer alleles that improve ability of population to adapt to local conditions

Question 48

does gene flow reduce or increase the differences between population

Answer 48

reduces

Question 49

give an example of gene flow

Answer 49

Spread of insecticide resistance amongst various mosquito populations

Question 50

what does sexual selection cause and what does that mean

Answer 50

sexual dimorphism (difference between the sexes )

Question 51

explain mate choice

Answer 51

Mate choice: (generally selection by females): may be at odds with other selective pressures – e.g. large colourful feathers on birds of paradise make you easier to spot by predators & mean you might have difficulty getting away)

Question 52

explain intrasexual selection

Answer 52

Intrasexual selection: competition amongst males for mating opportunities / dominance (e.g. size, ritual displays, combat)

Question 53

what do females use to measure the general health of a male

Answer 53

sexual advertisements

Question 54

What is a clue a female uses to measure the health of the male?

Answer 54

Individuals with infections or other problems may have relatively dull, disheveled plumage (unlikely to win favour amongst many females)

Question 55

What is the benefit of this females inclination after the visual signals

Answer 55

the benefit is a greater probability of having healthy offspring

Question 56

what are the 3 types of natural selection

Answer 56

- stabilizing selection - directional selection - disruptive/diversifying selection

Question 57

explain stabilizing selection | and what is its disadvantage?

Answer 57

Select against both phenotypic extremes Trend towards homogeneity (reduced variation) Generally occurs in a stable environment Disadvantage: if there is a sudden change & the stabilized phenotype becomes unfit, there is a greater risk of extinction

Question 58

give an example of stabilizing selection

Answer 58

e.g. Infant birth weight: relatively narrow range of birth weights for infants; too high or too low results in complications

Question 59

explain directional selection

Answer 59

Select for one phenotypic extreme Shifts allele frequency curve in 1 direction (move average) Allows for adaptation to new conditions Often caused by exposure to a changing or novel environment Artificial selection (breeding organisms to produce preferred phenotypes)

Question 60

give an example of directional selection

Answer 60

e.g. Bacterial resistance to antibiotics: if there is a range of resistance to an antibiotic within a population & it becomes exposed to this antibiotic, there will be directional selection towards individuals with resistance (those without will die)

Question 61

explain disruptive/diversifying selection

Answer 61

Disruptive / Diversifying Selection Favour 2 extreme phenotypes Select against the majority of the population (intermediate phenotypes) May be due to new barrier (disperse population) or change in conditions (average organisms perish) Often results in 2 sub-populations (may eventually become distinct species) Recall allopatric speciation e.g. Drought causing most common food source of Galapagos Finch to be lost: select for long beaks to catch wood-boring insects or thick beaks to eat cactus seeds (intermediate beak not as useful)

Question 62

give an example of disruptive selection

Answer 62

e.g. Drought causing most common food source of Galapagos Finch to be lost: select for long beaks to catch wood-boring insects or thick beaks to eat cactus seeds (intermediate beak not as useful)

Question 63

which selection favours the 2 extreme phenotypes?

Answer 63

disruptive

Question 64

which selection favours for 1 phenotypic extreme

Answer 64

directional

Question 65

which selection favours against both phenotypic extremes

Answer 65

stabilizing

Question 66

DIAGRAM OF SELECTIONS

Answer 66

SEE NOTES ON SLIDES