MODULE 2 OVERVIEW Flashcards
Define evolution
the cumulative change in a population or species over time
Define macroevolution
major evolutionary changes among large taxonomic groups (at or above the species level) over LONG periods of time
Define microevolution
evolutionary change within a species or small group of organisms, especially over a short period.
What are some agents of change in evolution?
- natural selection
- mutation
- sexual reproduction
- genetic drift
- gene flow
What is the Hardy-Weinberg theorem?
- gives us the GENOTYPE frequencies expected for any possible set of allele frequencies
- under certain conditions, allele frequencies WILLNOT change from one generation to the next
5 assumptions of HW theorem
- no migration
- no mutation
- equal fitness (no selection)
- random mating
- infinite population size
How can we tell if observed genotype frequencies are different to frequencies expected under HWE?
- Calculate allele frequencies using population genotypes
- Use HW equation to calculate EXPECTED genotype frequencies (NULL HYPOTHESIS)
- Chi-squared test
- Check to see if the chi-squared value is significant
Define population
group of organisms that interact and share genetic information
Why is it useful to define population?
- spread of disease
- track resistance (e.g. insecticide)
- risk of inbreeding
- financial - bioprospecting
- pest control, e.g. fox or feral cats
- conservation e.g. monarch butterflies
Define gene pool
all the genetic variation that exists among all the individuals of a population
Smaller populations are ___ susceptible to change
more
- also more susceptible to genetic drift + natural election
Define distribution
the area a population inhabits and density of the individuals
What is effective population size?
The effective population size is the size of an ideal population (i.e., one that meets all the Hardy-Weinberg assumptions) that would lose heterozygosity at a rate equal to that of the observed population.
Can somatic mutations get passed down?
No, not heritable generally, but can be passed down in plants e.g. through vegetative reproduction
Mutations in regulatory regions may affect. . .
gene expression
Mutations in coding regions may affect. . .
protein function (translation)
We know the small changes caused by mutations. What about the larger ones?
- DNA is copied a second time and/or flipped around (inversion + duplication)
- chromosomes are joined together or gained/lost (aneuploidy)
- entire genomes are duplicated
What kind of mutation is sickle cell anemia?
point mutation
What kind of mutation is down’s syndrome?
aneuploidy (extra chromosome 21)
What is the common mutation rate in humans?
approximately one SNP per 30 million base pairs
Why should evolution favour asexual reproduction?
- multiply faster
- search cost eliminated
- no risk of sexually transmitted infections
What are the benefits of sexual reproduction?
- combining beneficial alleles
- generation of novel genotypes
- faster evolution
- clearance of deleterious mutations
What is assortative mating?
like with like
= less genetic diversity
What is diassortive mating?
opposites attract
What are the 3 principles of natural selection?
1) variation
2) heredity
3) selection
What does the selection differential refer to?
the difference b/w population mean and selected mean
2 types of selection
1) directional
2) stabilizing
3) disruptive
Industrial melanism is what kind of selection?
directional selection
Selection acts on ___ alleles faster than on ___ alleles
Selection acts on dominant alleles faster than recessive alleles
Why is selection not likely to drive a dominant allele to FIXATION?
recessive alleles can HIDE in the heterozygous state
Why are favoured recessive alleles not exposed to selection initially?
- because they are likely to occur only in the heterozygous genotypes
- once recessive homozygous begin to appear, they quickly fit in the population
What is balancing selection?
heterozygous advantage occurs when selection favours heterozygous individuals over homozygous (e.g. sickle cell)
What is fitness?
the success of an organism at surviving and reproducing and thus contributing offspring to future generations
What is genetic drift?
involves RANDOM changes in allele frequencies that are directionless
‘sampling error’
The allele frequencies of the next generation are influenced by. . .
the ‘chance’ number of individuals that breed and the alleles they have
Genetic drift is most pronounced in. . .
SMALL populations
Large populations buffer genetic drift making it. . .
a LESS significant agent of change
populations don’t need to be infinite in size, but large enough that random sampling effects do NOT impact allele frequencies significantly
What is the founder effect?
when a small number of individuals found a new population
- random differences in allele frequencies occur when a small colony splits from a large population
What is genetic bottleneck?
caused by events that reduce the size and genetic diversity of a population significantly
e.g. a bushfire impacts allele frequencies in a population by CHANCE
What is the result of a genetic bottleneck?
populations contain a SMALLER, mostly RANDOM sample of the alleles that were present in the original ppopulation
3 issues of a genetic bottleneck
- increased homozygosity (issues arise in the case of recessive deleterious alleles)
- fixation of alleles (small populations affected more by genetic drift)
- less potential adaptive capacity (less variation for natural selection to work w)
The chance of losing alleles after bottleneck or founder events depends on. . . ?
1) their initial frequency
2) new population size
Following a bottleneck or founder event, population size. . .
may recover quickly
but genetic diversity will not
What are some implications of genetic drift?
1) conservation –> fragmented populations will continue to LOSE genetic diversity via drift
2) speciation –> populations that STOP exchanging alleles and continue to differentiate due to genetic drift and/or other agents of change may become separate species
What is gene flow?
the transfer of genetic info from one population to another and sharing of genetic info via migration, movement, or hybridisation
For gene flow to occur, individuals must be able to. . .
disperse
interbreed
produce viable offspring
Gene flow tends to . . .
homogenize more connected populations
A lack of gene flow promotes. . .
interpopulation differentiation
What is hybridisation?
interbreeding of individuals from genetically distinct populations or closely related species (offspring may be sterile)
- integration of alleles from diff genetic background
The IMPACT of gene flow on the gene pool depends on:
1) the extent of movement
2) the genetic difference between populations
What makes migration a significant evolutionary agent for a population?
1) when the difference in allele frequencies in residents (p) and migrants (x) is GREAT
2) when migration rate (m) is HIGH
Define speciation
the evolutionary process by which new species arise through reproductive isolation
Types of reproductive barriers
1) pre-mating reproductive isolation (geographic + behavioural isolation)
2) Pre-zygotic reproductive isolation (sperm can’t reach egg - timing + ecological isolation)
3) Post-zygotic isolation (prevents hybrid zygotes from developing / reproducing)
Allopatric speciation
speciation in DIFFERENT geographic locations
Sympatric speciation
speciation in the SAME location
What is adaptive radiation?
very rapid evolution of many species through adapting to underutilized ecological niches
Why is it useful to define a species?
- conservation
- food
- safety
- medical
- recreational (catch limits when fishing)
What is adaptive introgression?
inheritance of beneficial variation from related species that accelerate adaptation to, and survival in new environments
What is introgression?
describes the movement of alleles from one species or population to another
What is lignin?
a polymer deposited predominantly in the walls of plant cells, providing structure and making them rigid
Molecular genetics
involves the study of DNA sequences encoding specific GENES to understand FUNCTION
Genomics
the study of the DNA sequence of all the organism’s genes
How is variation investigated (using genomics)?
1) compare specific situations (controls vs cases)
2) look across the distribution of a phenotype
3) look at the evolutionary relationships
Genomic analysis of many individuals
1) collect samples
2) create libraries
3) investigate one gene / genome
4) identify SNPs & other genetic variaitons
What is phylogenetics?
the study of evolutionary relationships among biological organisms based on:
1) similarities / differences in DNA
2) molecular clocks
3) phenotypes
4) fossil record (used for calibration)
