Exam 1 Flashcards
Natural selection
changes in gene frequency due to differential fitness associated with phenotypes or genotypes
Mutation
any change to the genomic sequence
What are the four postulates of natural selection
population contains variation, some of that variation is heritable, populations produce more offspring than can survive, survival and reproduction are non-random
Evolution
change in gene/allele frequencies in a population over time
adaptation
inherited aspects of an individual that allow it to outcompete other members of the same population that lack the trait
What are the types of selection that populations can experience
negative frequency dependece which favors rare alleles and positive frequncy dependence which favors common types
What are the limits of natural selection
Genetic (need to have thing to select), physiological, developmental, time (selection needs tie to act), and history (unpredictable conditions can quickly turn evolution in a different direction)
Central dogma
DNA to RNA to protein to amino acids
Where does variation in populations come from and what are examples
new mutational input (point mutation, insertion, deletion, gene duplication, and inversion) and recombination (genetic variation via crossing over of alleles)
Genetic Drift and what are the types
random, non-representative sampling of alleles from a population
- mendelian lottery, founder effect, and bottleneck
mendelian lottery
Transmission of alleles to particular gametes is affected by chance since populations are finite
Founder effect
populations founded by a small number of individuals can give very different gene frequencies than that of the parent population
What is an example of founder effect
present day Amish communities settled in the US have a large proportion of 4 recessive disorders due to them being present in the founding population (hemphilia B and Ellis-van Creveld syndrome)
Bottleneck
Population size reduced and only a few individuals survive to breed
- Similar to founder where some alleles can disappear and rare alleles become very frequent
-Makes a population have a less effective immune system
What is an example of bottleneck
When cheetahs nearly went extinct 10,000 years ago and now are all genetically identical
What are the effects of genetic drift on a population
Reduces genetic variation in a population, random fixation of alleles (especially in small population sizes), loss of heterozygosity (one allele drifts toward fixation), and has a larger effect in smaller populations
Phenotypic redundancy and example
different phenotypes have the same fitness. Example is a small population of E. coli having thousands of generation leading them to differ little to each other but had increased fitness compared to ancestor
What are the principles of HW and its assumptions
-Allele frequencies remain constant unless acted upon by some outside force
-Once genetic variation is introduced into a population, it’s preserved
-Describes populations that are not evolving
Assumes there is no selection, migration, or mutations and random mating and an infinite population size
What are the curves on a basic population genetic model and the effects of selection
Asexual curve increases the quickest and exponentially, sexual dominant curve increases nearly as fast but flattens out, sexual recessive curves is near zero for a while before increasing exponentially near the end
- evolutionary change is fastest at intermediate allele frequencies
- asexuals have shorter generations thus, change over time at a faster rate
What does the outcome of selection depend on
frequency of allele and its effects on fitness
What size of population does genetic drift and natural selection affect the most
Genetic drift is more powerful in small populations while natural selection is more powerful in large populations
Example of lab evolution studies reveal how alleles rise and spread through populations
in flour beetle populations, one allele is lethal recessive while the other is normal. Started with a heterozygous population and over time lethal allele was selected agaisnt while the other was selected for
What is an example of a natural experiment to conform to simple models
use of pesticides in the 40s was initially effective but by the 70s insects evolved to develop resistance
Pleiotropy and what is an example
Mutation in a single gene affects many phenotypic traits. Example is sickle cell anemia where heterozygosity increased fitness in areas with and without malaria but homozygotes with sickle cell had less fitness in general while normal homozygotes had worse fitness in areas with malaria
What are the effects of migration
potentially increase genetic variation and the effective population size. Can lead to maladaptive alleles in a population
Additive allele
allele that yields twice the phenotypic effect when two copies are present at a given locus than when only a single copy is present
Polygenic trait and what are the types
influenced by two or more genes. Epistasis (interaction between alleles) and phenotypic plasticity (interaction with environment)
Quantitative genetics
Study of the genetic mechanisms of continuous phenotypic traits
What are two types of heritability
broad sense: how much of the phenotypic variance is due to genetic variation and narrow sense: what percentage of phenotypic variation is due to additive genetic variance
Phenotypic plasticity
When a single genotype produces different phenotypes depending on the environment
What is the neutral theory of molecular evolution
describes patterns of nucleotide substitution predicted under drift alone. Suggests that most evolutionary change at the genetic level is due to genetic drift, as most mutations are neutral/nearly neutral
Homoplasy
when 2 things share a common state, due to mutation, but not due to common descent
What is the fate of duplicated genes
Death, neofunctionalization (gets a new job), and subfunctionalization (each gene in the pair specializes in one job)
How you tell when a trait is an adaptation
if the trait is heritable, value of the trait is related to fitness
What are the two main types of evolution
Convergent: similar traits evolve in separate species due to being in a similar environment. Divergent: single species branches off into more than one
Disruptive selection
selects agaisnt the intermediate
Stabilizing selection
Selects for the intermediate
Directional selection
Selects for one of the extremes
When drawing a quantitative trait graph what would be on the axes
Frequency would be on the left while trait value would be on the bottom
