Genetic Variation (PP17) Flashcards
explain Quantitative characters:
vary along a continuum / spectrum within a population
Usually due to polygenic inheritance (additive effects of 2 or more genes influence single phenotypic character)
explain Discrete characters:
generally an either-or
Usually determined by a single locus with different alleles with distinct impacts on the phenotype
explain polymorphism
When 2 or more discrete characters are present & noticeable within a population
polymorphism applies to what characters?
Applies only to discrete characters, not quantitative characters
what are contrasting forms called?`
morphs
give an example of morphs
Red-flowered & white-flowered morphs in a wildflower population, or butterflies
are humans polymorphic
YES
Human populations are polymorphic for a variety of physical (e.g. freckles) & biochemical (e.g. blood types) characters
what does gene diversity measure
Gene diversity: measures average % of gene loci that are heterozygous
what does nucleotide diversity measure
Nucleotide diversity: measures the level of difference in nucleotide sequences (base pair differences) among individuals in a population
what do population genecists measure
Population geneticists measure genetic variation both at the level of whole genes & at the molecular level of DNA
do Humans have relatively little or a lot genetic variation compared to many other organisms
a little
What equation shows Evolution of a population can be explained as changes in allelic frequencies over time
Hardy-Weinberg Equilibrium
If certain conditions are met, allelic (genotypic) frequencies will not change
Genetic frequencies will stabilise to certain proportion:
p2 2pq q2
What conditions does the hardy-weinberg equilibrium need to met.
Large population No mutation (no new alleles) No migration (isolated) No natural selection No sexual selection (random mating)
What happens when all conditions of hardy-weinberg met?
If all of these conditions are met, then we arrive at HW equilibrium:
can a population be in HW equilibrium for 1 locus but not others?
yes
what are genetic frequencies determined by?
Allelic frequencies
LOOK AT SLIDES FOR HARDY WEINBERG EQUATION
LOOK AT SLIDES
explain fitness
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)
fitness equation
LOOK AT SLIDES
What does the most prolific genotype mean and what fitness (W) does it have?
Most prolific genotype means the one that produces the most offspring
Most prolific genotype is considered to have fitness (W) of 1
what are the two ways of genetic variation
Mutations
-allele resorting
how do you get new alleles
due to changes in nucleotide bases
true or false: Mutations are Continuous, spontaneous, unpredictable, but inducible
-ONly Mutations that are present in gametes will be passed on
true
true
name the ways of allele resorting
- Sexual reproduction (two different parents)
- Segregation of alleles from different parents into different gametes
- Crossing-over
- Random fertilization
explain macroevolution
Large-scale changes in organisms (obvious differences in traits)
These changes are observable only after many generations
explain microevolution
Generation-to-generation change in allele frequency in a population
Generally fairly subtle changes
what is one difference between macro and micro evolution and one similarity?
DIFFERENCE:
Examination of the same process at different scales
SIMILAR:
Both are due to non-random selection of random variation
what are the 4 definitions of a species
Biological Species Concept:
Morphospecies Concept:
Ecological Species Concept:
Phylogenetic Species Concept:
explain biological species concept and why would the definition not be true?
- Organisms considered to be of same species if they can produce viable & fertile offspring
- because of two barriers: PostZygotic and PreZygotic
Explain Prezygotic Barrier
Pre-zygotic: before a sperm and egg cell even get the chance to fuse
“Causes for reproductive isolation”
explain Post zygotic barrier
Post-zygotic: diploid cell is created, but fail to produce an organism that meets the definition of a species according to the above definition
explain the morphospecies concept
Different species will look different - based on the morphology (physical characteristics)
explain ecological species concept
Species defined based on role within ecosystem - each species will have a distinct role (“niche”)
explain the phylogenetic species concept
Species determined by proximity / grouping on a phylogenetic tree - if grouped together, considered the same species.
what are the prezygotic factors
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)
what are the post zygotic factors (ie. why they can reproduce)
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
what are the two types of speciation
Allopatric speciation
Sympatric speciation
explain allopatric speciation
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
explain sympatric speciation
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)
What are the 5 factors that determine Allele frequencies
Mutation Genetic Drift Gene Flow Sexual Selection Natural Selection
explain genetic drift
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)
what are the two important mechanisms in genetic drift
2 important mechanisms:
Bottleneck effect
Founder effect
explain the bottleneck effect
SEE DIAGRAM IN SLIDES
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)
give examples of bottle neck effect
insect survival through the winter, at-risk/endangered species (Florida Panther)
explain the founder effect
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)
give example of founder effect
Prevalence of Huntington’s disease amongst Afrikaners (South Africa) due to presence of disease in small population of Dutch settlers
explain gene flow
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
does gene flow reduce or increase the differences between population
reduces
give an example of gene flow
Spread of insecticide resistance amongst various mosquito populations
what does sexual selection cause and what does that mean
sexual dimorphism (difference between the sexes )
explain mate choice
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)
explain intrasexual selection
Intrasexual selection: competition amongst males for mating opportunities / dominance (e.g. size, ritual displays, combat)
what do females use to measure the general health of a male
sexual advertisements
What is a clue a female uses to measure the health of the male?
Individuals with infections or other problems may have relatively dull, disheveled plumage (unlikely to win favour amongst many females)
What is the benefit of this females inclination after the visual signals
the benefit is a greater probability of having healthy offspring
what are the 3 types of natural selection
- stabilizing selection
- directional selection
- disruptive/diversifying selection
explain stabilizing selection
and what is its disadvantage?
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
give an example of stabilizing selection
e.g. Infant birth weight: relatively narrow range of birth weights for infants; too high or too low results in complications
explain directional selection
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)
give an example of directional selection
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)
explain disruptive/diversifying selection
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)
give an example of disruptive selection
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)
which selection favours the 2 extreme phenotypes?
disruptive
which selection favours for 1 phenotypic extreme
directional
which selection favours against both phenotypic extremes
stabilizing
DIAGRAM OF SELECTIONS
SEE NOTES ON SLIDES
