Evidence for Evolution/Mechanisms of Evolution Flashcards
What are the 4 mechanisms for evolution??
- Mutations
- Gene flow
- Natural selection (including sexual selection)
- Genetic Drift
Evolution - Definition
change in the (heritable) characteristics of a population over generations
- can be micro or macro
Microevolution
Changes in allele frequencies in POPULATION over short period of time (EX ONE GENERATION)
Macroevolution
occurs at or above the species level - how new species arise. occurs over long time periods
whats the current theory of evolution??
we’re all descended from single celled ancestor (LUCA - Last Universal Common Ancestor) which existed around 3.7 billion years ago
species change through time
species can go extinct
evidence that all species share a common a common ancestor
- all living things are made of cells
- the universality of DNA as the genetic code
- universal flow of biological info (DNA to RNA to amino acids/proteins)
- almost universality of genetic code (codons) and DNA replication/repair
what does all species sharing common ancestor help us do
use bacterial gene editing to edit our genome (CRISPR-Cas9)
crazy things like insert jellyfish gene that codes for green light protein into a cat
evidence that species are related to each other (evolutionary relatedness)
homologies
traits present in two or more organisms INHERITED FROM THEIR COMMON ANCESTOR
homologies can be…
- anatomical/structural
- developmental
- genetic
anatomical/structural homologies
ex in bone structure - human, horse, seal, turtle etc all have a humerus, radius, ulna, carpals, metacarpals, phalanges
homologous structures may not look the same in different species and may not have the same function
developmental homologies
developmental similarities in early embryonic stages (because of inheritance of developmental processes from a common ancestor)
ex humans had gills and tails during development, developmental homology with cats and chickens
genetic homologies
genetic similarities between organisms due to common ancestry
ex. human and chimp DNA is about 99%
since some dna sequences can code for the same proteins, its possible for two species to have around 85% genetic similarity but 100% protein similarity in a specific gene
analogous traits/homologies
occur as an independent solution to an environmental demands - CONVERGENT EVOLUTION
convergent evolution
independant solution to an environmental demand
evidence that species have changed with time
- extinctions in the past and today
- transitional fossils
- vestigial traits
- real time evidence of change
evidence of evolutionary change from fossil record
looking at fossils from the past and comparing to animals now - show that life on earth was once different from life on earth today
evidence of evolutionary change - transitional fossils
transitional/intermediate forms showing intermediate anatomy between early and later forms of species
evidence of evolutionary change - vestigial structures
structures w/ reduced or no function compared to ancestral form due to evolution
ex of vestigial structures
pelvic bones in whales and dolphins from when ancestors walked on land 40 mill years ago
humans - smooth muscles in skin called arrector pili, make us get goosebumps, also ear muscles to change direction of ears
real time evidence of evolutionary change
evolution of antibiotic resistance in bacteria - populations can change overtime but always over generations
mechanisms of evolutionary change
- mutations
- gene flow
- natural selection (inc sexual selection)
- mutations
Mutation definition
any change in the nucleotide sequence of DNA
- can range in size from one nucleotide to large segments of a chromosome that affect multiple genes
point mutation OR ____
SNiP - and mutation that alters a single base pair, or small number of adjacent base pairs
what does SNiP stand for
single nucleotide polymorphism
main causes of point mutations
- errors during DNA replication (most commonly)
- errors during repair of DNA damaged by radiation/chemical mutagens
more causes of mutations (more than just SNiP)
NOT TESTABLE
- unequal crossing over
-chromosome inversion from DNA breakage (radiation)
where can mutations occur/what does that mean?
mutations can occur in germline and somatic cells
somatic cells - not heritable, confined to one cell, and may not affect individuals during their lifetime
germline cells - in gametes, significant for evolution because HERITABLE, could potentially affect every cell in the body
how can mutation vary amongst species??
if undergo mitosis/meiosis more frequently - higher mutation rates (most mutations occur in DNA replication)
org. that reproduce more quickly pass on those mutations faster (IF mutations in germline cells)
org. that invest more in DNA protection and repair lower mutation rates
pros and cons high mutation rate?
pros, population can aquire new phenotype/adapt to new environments more quickly
cons, easier to lose current adaptations
darwinian fitness
measures the relative reproductive success
OR
individuals relative contribution of genetype/phenotype to future generations
neutral mutations
mutations are random, not related to how helpful it would be
only 2% of our DNA codes for proteins, so mutation in non coding regions wouldn’t affect phenotype/fitness
codon is also written in 3 letter codes, multiple codons creating the same amino acid so a a mutation in coding region may not affect the individual at all
harmful mutations
reduce an organism’s fitness, reduce survival/fertility
ex. cystic fibrosis, cancer
beneficial mutations
increase an organism’s fitness, increase likelihood of survival ^ fertility
how the environment affects the fitness effects of mutations
ex sickle cell anemia - recessive allele produces abnormal hemoglobin proteins in red blood cells (makes them sickle shaped)
cons - reduced oxygen carrying capacity, oxygen deprivation can lead to organ damage and stroke, blood cells break down prematurely - anemia
pros - carriers are resistant to malaria, mutation is beneficial where malaria is common but harmful where malaria is rare
what makes mutations beneficial??
- ultimate source of genetic variation
-generates new allels
-new phenotypes
-raw materials for evolution to take place
-EVOLUTION COULDN’T OCCUR WITHOUT THEM
are mutations a strong or weak evolutionary mechanism?? why??
weak!
- most are silent/neutral w respect to fitness
- mostly only affect one individual (unless occuring in germline cells)
- takes other evolutionary mechanisms to increase/decrease new allele in population
- only mutations with strong selective advantage are likely to sweep through population
gene flow definition
the movement of alleles between populations caused by dispersal (of individuals or gametes) and mating
change allele frequencies in new population/introduce new alleles
what happens when individuals are moving between populations (gene flow)??
homogenizes allele frequencies between populations over time
what happens when little to no gene flow?
genetic divergence between population - if this continues it can lead to speciation
Natural selection
Non-random differences in the survival and reproduction of individuals with certain genotypes/phenotypes in population over generations
three requirements for natural selection to occur *****
- VARIATION in trait/phenotype amongst individuals (selection acts on the phenotype)
- DIFFERENCES IN FITNESS associated with the different phenotypes
- the phenotype must be HERITABLE - so survivors leave more offspring w/ the same phenotype
randomness with mutations and selections
mutations are random w/ respect to fitness, but the probability of that allele passing onto the next generation is NOT random
adaptations
process in which individuals become more well adapted to environment as a result of mutations/natural selection
OR
heritable trait that ^ ability of an individual to survive and reproduce compared to individuals without the trait
what can adaptations be??
structural, physiological, behavioural
a trait is NOT an adaptation if…
- not heritable
- not functional
- does not affect fitness
if asked a question about whether natural selection has occured, what should you include???
the three requirements for natural selection to occur - heritable, variation in phenotype, differences in fitness associated with diff phenotypes
if asked a question about whether natural selection has occured, what should you include???
the three requirements for natural selection to occur - heritable, variation in phenotype, differences in fitness associated with diff phenotypes
three modes of natural selection
- directional
- stabilizing
- disruptive
directional selection
favours individual w phenotype at one end of spectrum, frequency distribution of the trait is shifted in the direction of the favourable trait
OUTCOME - changes average value for trait in population & decrease in phenotypic variation
can change directions
stabilizing selection
favours intermediate phenotypes, selects against phenotypes at extreme ends of the spectrum
OUTCOME - average value of the phenotype remains the same, phenotype/genotype variation is reduced
ex baby weight, not too heavy or too small, also robins lay 4 eggs, too little and none may survive, too many not enough food to go around
disruptive selection
phenotypes at either end of the spectrum favoured, not intermediate phenotypes
OUTCOME - average value of the trait remains the same, increase in phenotypic variation
ex small and sneaky chinook salmon vs large and fighty salmon, middle no
trends in directional, stabilizing, and disruptive selection
DIRECTIONAL - average trait value increase or decrease, phenotypic variation reduced
STABILIZING - average trait value same, phenotypic variation reduced
DISRUPTIVE - average trait value same, phenotypic variation increased
how sexual selection came about
natural selection is largely ecological, but traits were observed that logically wouldnt actually benefit the individuals fitness. An explanation for this is that those traits make the individual more likely to find a mate and reproduce
sexual dimorphism
distinct differences in size, appearance, behaviour, physiology between males and females
two mechanisms of sexual selection
- intrasexual selection (competition for mates, mostly male-male)
- intersexual selection (mate choice, female choice mostly)
intrasexual selection
can involve physical battles between males, more outward displays of dominance (ex size) or sneaky/indirect tactics
copulatory plug, scoop shaped penis, marking females, destroying sperm etc
what is male fitness linked to
number of mating opportunities
asymmetric cost of reproduction
females invest much more time and energy into reproduction and caring for offspring compared to males
two things that would make a male more enticing to a female
- male better at providing direct benefits - food, shelter, protection
- male better indirect benefits - good genes, maximize fitness of the females offspring
direct benefits from males
male signal that they would provide good parental care
ex. female lions preferentially mate with lions with darker manes, this signals, older age (survivor) high testosterone levels (fighting ability), good protector
males could demonstrate that they can provide resources by bring gifts (nuptial gift)
indirect benefit
phenotype is an indicater of good genes/high fitness could be passed to females offspring
look fab! - healthy, good immune system, non-damaged dna
artificial selection
people rather than nature select which individuals get to reproduce and pass genes onto the next generation
again! what are the 4 mechanisms of evolution
- mutations
- gene flow
- natural selection
- genetic drift
genetic drift definition
drifting of allele frequencies over time due to RANDOM differences in survival and/or reproduction
what sort of population does genetic drift affect more??
small populations, which tend to lose genetic diversity more quickly
what in math is genetic drift equivalent to
sampling error, like flipping a coin twice and getting heads twice. doesnt mean 100% chance of heads just random
what in math is genetic drift equivalent to
sampling error, like flipping a coin twice and getting heads twice. doesnt mean 100% chance of heads just random
what are two opportunities for genetic drift??
- Population bottle neck event
- current population decreases by large amount, likely diff allele frequency - Founder effect
- new population founded, allele frequency different from parent population
- both involve a change in population size, one where result is substantially smaller than original
population bottleneck event
population size is greatly reduced over a very short period of time, usually due to a natural disaster such as a wildfire etc
all down to chance, wrong place at the wrong time, so could not change allele frequency at all or could change it a lot!
founder effect
new population is founded be a few individual, founders isolated from og population so no gene flow
allele frequencies in new pop can be very very different from original
very bad founder event
invasive species :(
can be significant losses in allelic diversity in new population
disrupts ecosystems
can genetic drift happen without reduction in population size??
YES!!! could just be completely random and related to reproduction rather than survival, right place at right time
potential impacts of genetic drift
if a large loss of genetic diversity occurs, populations can lose important physiological features, resistance to diff things, adaptations etc. ex when northern elephant seal population reduced greatly, lost skull symmetry
differences between genetic drift and gene flow
genetic drift involves movement within a population whether thats reduction in size or moving to a new place, can increase or decrease the frequency of an allele but can’t introduce new ones founder effect specifically reduces genetic variation
gene flow could introduce a new allele because of individuals from another population joining the current one - MOVEMENT OF INDIVIDUALS OR ALLELES, could increase genetic variation
genetic drift v natural selection
genetic drift involves random sampling, while natural selection is specific
genetic drift is unpredictable while natural selection is
MUTATIONS (summary)
change in an individuals DNA, must occur in gametes in order to be a mechanism of evolution, random, weak force but very important
EFFECT ON GENETIC VAR: increases genetic variation by introducing new alleles
EFFECT ON AVG FITNESS: not all have an affect, many are neutral, can be harmful or beneficial, and can depend on environment
GENE FLOW (summary)
changes in allele frequencies from movement of individuals or gametes between populations
EFFECT on GEN VARIATIO: could increase by incroducing new alleles recieving population, decrease by removing alleles from giving poplation, can also HOMOGENIZE populations
EFFECT on AVG FITNESS: could increase, decrease, or no effect on fitness depending on the allele
NATURAL SELECTION (summary)
Individuals with heritable trait have higher fitness than without, NON RANDOM, requires; a)heritable b)variation c)diff in fitness between variations
EFFECT on GEN VARIATION: generally decrease genetic variation unless disruptive selectioon
EFFECTS on AVG FITNESS; gen increase fitness over time
GENETIC DRIFT (summary)
changes in allele frequencies over time due to chance/random events
EFFECTS on GEN VARIATION: generally reduces variation
EFFECTS on AVG FITNESS: generally random w respect to fitness, or reduces avg fitness
