2-Evolution Mechanisms Flashcards
biological evolution
refers to a change in the (heritable) characters of a population over generations
microevolution
changes in allele frequencies in a population in a relative short period of time (one generation)
macroevolution
evolution that occurs at or above the species level
- how do new species arise
- Typically occurs over longer periods of time
current theory for evolution
- all species are related
-
Current theory—we all descended from a single called common ancestor (LUCA)
- ~3.7 billion years ago
-
Current theory—we all descended from a single called common ancestor (LUCA)
- Species change over time
- Species do go extinct
EVIDENCE THAT ALL SPECIES SPECIES SHARE A COMMON ANCESTOR
- all living taxa are made of Cells
- universality of DNA as the genetic code
- universal flow of Biological information
- DNA to RNA to amino acids/proteins
- Near universality of the Genetic code (codons) and DNA replication and repair
Can
Dogs
Beat
Goats?
HOMOLOGIES
EVIDENCE OF EVOLUTIONARY RELATEDNESS
traits present in two or more organisms that were inherited from their common ancestor
- anatomical /structural homologies
- Developmental homolgies
- Genetic homologies
homologies structures may or may not be modified in different taxa
- may not look the same (though they often do)
- Nor may they have the same function in different taxa
shared ancestry
allows us to study other organisms and apply that knowledge to help us
analogous traits or homoplasies
- arise due to convergent evolution
- Not inherited form a common ancestor
- Streamlined shape and finds represent a similar solution to the same environmental demand (moving efficiently through the water)
convergent evolution
Independent soleution to an environmental demand
evidence that species have changed with time
-
extinctions — in the past (fossils) and today
- Evidence of evolutionary change through time on the fossil record
-
Transitional fossils
- Transitional/intermediate forms showing intermediate anatomy between earlier and later forms
-
Vestigial traits
- Structures that have reduced function or no function compared to its ancestral from due to evolution
-
Real time evidence of charge
- Evolution of antibiotic resistance in bacteria
mutation
any change in the nucleotide sequence of the DNA
germline mutations
- occur in gametes (eggs or sperm)
- Germline mutations Especially significant for evolution because they can be transmitted to offspring!!
Somatic mutations
- occur in other cells in the body
- Not heritable!
- Confined to one cell
- May or may not affect individuals during their lifetime
what causes high mutation rates?
- organisms that undergo meiosis/mitosis more frequently—higher mutation rates
- Most mutations occur due to errors in DNA replication
- Organisms that reproduce more frequently will pass on those mutations to the next generation at a faster rate if mutation in germline cells
Organisms that invest more in DNA protection and repair will have LOWER mutation rates
adaptations definition
a structural, functional, or behavioural characteristic of an organism that helps individual survive/reproduce
Evolutionary (Darwinian) fitness
a measure of the relative reproductive success of individuals/an individual’s relative contribution of genotype (or phenotype) to future generations
Individuals that pass more genes to the next generation have a higher evolutionary fitness than individuals that pass fewer genes to the next generations
silent mutations
Any mutation in the non-coding region is unlikely to affect the phenotype/fitness of an individual
codon
3 letter combinations of nucleotides, writes the genetic code
amino acid
building block of proteins, is coded for by more than one codon
why are mutations a weak evolutionary mechanism?
- most mutations are silent/neutral with respect to fitness—do not matter to evolution
- Mutations only affect one individual
- Must occur in a germline cell to be passed on to future generations
- It takes other evolutionary mechanisms (natural selection) to increase or decrease the new allele frequency in the population
sickle-cell anemia
- genetic disease caused by a recessive allele that produces abnormal hemoglobin proteins in red blood cells
- Reduce oxygen carrying capacity of the blood
- Blood cells break down prematurely, leading to anemia
- But… carriers (heterozygotes) are resistent to malaria
gene flow
refers to the movement of alleles between populations caused by dispersal (of individuals or gametes) and subsequent mating
what happens if no gene flow?
- genetic divergence of the two populations
- Can lead to speciation
who introduced the idea of natural selection?
charles darwin and. Alfred Russell Wallace. Introduced idea in 1800s
natural selection
non-random differences in the survival and reproduction o f individuals with certain genotypes and the associated phenotypes in a population over time, generations
three requirements for natural selection to occur
- variation in trait/phenotype in population
- Diffferences in fitness associated with the difference in phenotypes
- Phenotype must be heritable (genetic component)
outcome of natural selection
- increase in frequency with the advantageous phenotype in population over generations
- Increase in frequency of the beneficial allele
- Population becomes more well adapted to the environment
- If environment changes, so can the direction of selection
ADAPTATIONS (OR ADAPTIVE TRRAITS)
Refer to a heritable trait that increases the ability of an individual to survive and reproduce compared to ppl without that trait
when is something NOT an adaptation?
- not heritable
- No function
- Does not affect fitness
directional selection
favours individuals with a phenotype at one end of the distribution of a trait
outcome:
frequency distribution of the trait in the subsequent generation is shifted in one direction from where it was in the parental generation
- average value for a trait is CHANGED!!
- variation (genotypic/phenotypic) tends to DECREASE
- STABILIZING SELECTION
selects against extreme phenotypes at both ends of the frequency distribution
favours intermediate phenotypes, removes extreme phenotypes
outcome:
- average value of the trait remains the SAME
- phenotypic/genotypic variation is REDUCED
- DISTRUPTIVE SELECTION
both extremes are favoured at the expense of intermediate phenotypes
- average value of the trait remains the SAME
- increase in phenotypic variation (?)
- often drives speciation!!!
THEORY OF SEXUAL SELECTION
certain conscpicuous traits that potential decrease survival could be selected for if they gave an individual an advantage for reproduction, either by:
- enabling an individual to outcompete rivals for access to a mate
- increasing the likelihood that an individual would be able to woo a prospective mate
sexual dimorphism
distinct differences in size/appearance/behaviour/physiology between males and femals
the two mechanisms of sexual selection
intrasexual selection
- competition for mates
- male-male interactions (mostly)
intersexual selection
- mate choice
- female mate choice (mostly)
Intrasexual selection COMPETITION FOR MATES—DIRECT MALE-MALE INTERACTIONS
- males may physically combat each other
- males may evolve “weapons” that give them an advantage in a fight
- but… does not always involve direct combat! maybe ornaments and behaviours? maybe mimicry? etc.
Direct benefit
males can signal that they would provide good parental care
- providing shelter from the environment
- protecting female and/or young from threats such as predators
- can provide resources to the female by bringing gifts
indirect benefit
male’s phenotype is an indicator or advertisement for good genes/high fitness that can be passed to the female’s offspring
- usually means the signal has to bear some cost to the female
- LOOKING BEAUTIUFUL? MEANS DISPLAYING THEIR GOOD GENES!
- healthy—no parasites
- good immune system
- non-damaged DNA, etc
Artificial selection
people, instead of nature select which individuals get to reproduce and pass their alleles onto the next generation
GENETIC DRIFT
changes in allele frequencies in a population over time due to random differences in survival and/or reproduction
changes in allele frequencies are not a function of whether the alleles are harmful or beneficial
- occurs in all populations that are not infinite in size
- outcome is due to chance!—sampling error
genetic drift on small populations vs large populations?
- random fluctuations in allele frequencies tend to be more pronounced in smaller populations than larger populations
- small populations tend to lose genetic diversity more quickly than larger populations
the opportunities for genetic drift
- (population) bottleneck event
- founder event
- both events involve a change in population size
- new population smaller than original population
- allele frequencies in a population can ALSO change by due to chance events with no change in population size
Population bottleneck Event
population size is greatly reduced (often over a short time period) for at least one generation (usually due to a catastrophe such as wildfire, flood, etc)
founder event:
occurs when a new population is founded by a few individuals
Transitional fossils
Transitional/intermediate forms showing intermediate anatomy between earlier and later forms
Vestigial traits
Structures that have reduced function or no function compared to its ancestral from due to evolution
how to tell when something is an adaptation?
Heritable – It has a genetic basis
Functional
Adaptive - Trait must increase the fitness of the organism compared to organisms lacking the trait
Current function – The trait evolved at the same time as the current function.
