Microevolution Flashcards
Term that applies to evolutionary change within a lineage.It occurs continuously. Depending upon the organism and the circumstances, it can transform a lineage dramatically over time.
Microevolution
Alternately, a lineage may appear to remain the same over time-this is called
Stasis
Term that applies to the origin and extinction of lineages. It can happen gradually, or slowly.
Macroevolution
Which type of evolution do we understand better? Why?
Microevolution because it takes place on appropriate timescales that we can study directly
Did Darwin include a mechanism for the origin of species in his microevolution theory?
No.
Is the replacement of one species by another natural selection?
No. It is an ecological process with macroevolutionary implications
Is the genotype of an individual fixed at birth?
Yes
Then what is the smallest unit where evolutionary change is possible?
Do individuals evolve?
Populations
No
Populations permit the origin of new alleles through…
They permit change in the frequency of alleles through…
Mutation
Selection, Genetic Drift
refers to the study of evolution via the observation and modeling of allele frequencies and genetic change in populations of organisms.
Population Genetics
the proportion of a specific allele at a given locus, considering that the population may contain from one to many alleles at that locus.
Allele Frequency
The proportion of a specific genotype at a given locus, considering that many different genotypes may be possible
Genotype Frequency
The proportion of individuals in a population that exhibit a given phenotype
Phenotype Frequency
count the number of individuals with that phenotype, and then divide by the total. This gives you…
Phenotype Frequency
find the total number of individuals in the population with that genotype, and divide by the population size, N
Genotype Frequency
The formula for allele frequency for heterozygotes and homozygotes using alleles
p = (#AA) + 0.5*(Aa)/N q= (#aa) + 0.5*(Aa)/N
The formula for allele frequency if you know the genotype frequencies
p=[f(AA)+0.5* f(Aa)]/N
q=[f(aa) + 0.5* f(Aa)]/N
Evolutionary Change is a Consequence of Changes in…
Is this macroevolutionary or microevolutionary change?
Allele Frequencies
Microevolutionary Change
All of the evolutionary change between our single-celled ancestors and ourselves can be described as the sequential origin of new alleles, their replacement of old ones, and occasionally the origin of new genes through duplication.
!!
defined as the situation in which no evolution is occurring. It is a genetic equilibrium.
Hardy-Weinberg Equilibrium
Was the notion that the dominance or recessiveness of an allele alone cause evolutionary change?
No.
Does Hardy Weinberg Equilibrium refer to one particular locus or multiple?
One lucus. It may be undergoing rapid allele-frequency change, while other loci are in equilibrium.
The five assumptions of hardy weinberg equilibrium
Infinite Population Size No Allele Flow No Mutation Random Mating No Selection
there are infinitely many individuals in the population
Infinite Population Size
no movement of individuals from population to population
No Allele Flow
no biochemical changes in DNA that produce new alleles
No Mutation
this means that with regard to the trait we’re looking at, individuals mate at random they don’t select mates based on this trait in any way
Random Mating
the different genotypes (for the genetic trait we’re studying) have equal fitness
No Selection
Genotype frequency for AA
for Aa
for aa
p^2
2pq
q^2
One of five ways in which evolution occurs in which the five assumptions of HW are not met: A change in allele frequency by random chance. It occurs if a population is not infinite in size.
Genetic Drift
The effect of genetic drift is larger or smaller in small populations.
larger
In populations that are not infinitely large, there will be random error in which alleles are passed from generation, and allele frequencies will change at random.
!!
change in allele frequency that occurs because individuals move among populations
Allele Flow
biochemical change in DNA that one allele into another and creates alleles. It not a common event as a result, evolution through this is extremely slow.
Mutation
(typical mutation rates are about one mutation in a million genes passed from generation to generation );
!
Ultimately is the source of genetic variation
Mutation
Is fitness of mutations always good? Or is it random?
Do they result in higher or lower fitness more frequently?
Random
Lower
Note: the probability of a mutation occurring is independent of the need for one
!!
evolution that occurs because individuals select mates based on their characteristics.
Random Mating
evolution that occurs because different genotypes have different fitness. More about this later.
Natural Selection
Mutations may affect somatic tissue, also called
Mutations may affect the germ line, also called
Non-reproductive Tissue
Reproductive
In general, can somatic mutations be passed on?
No. Exception: Clonial Organisms
Mutations that can be passed to the next generation
Heritable Mutations
Whether a mutation is harmful, neutral, or favorable, depends upon
The environment
Type of mutation where one nucleotide is substituted for another, frequently this causes no change in the resulting organism, sometimes the change can be dramatic.
Substitution
Type of mutation where DNA is inserted into a gene, either one nucleotide or many. Sometimes, entire genes are inserted by viruses and transposable elements.
Insertion
Type of mutation where DNA bases are removed.
Deletion
Small insertions and deletions can inactivate large stretches of a gene, by causing this - which renders a gene meaningless
Frame Shift
Type of mutation where an entire gene is duplicated.
Duplication
Type of mutation where DNA is moved to a new place in the genome, frequently this happens because of errors in meiosis or transposable elements.
Transposition
their occurrence is independent of their selective value - i.e., they do not occur when they are needed any more often than they would otherwise.
Mutations are random events
Mutations at any single locus are rare events, mutation rates at a typical locus are about 1 in 10^6 gametes
!
Since each individual has thousands of alleles, the cumulative effect of mutations is considerable:
Consider that each gamete has 2x104 loci, and the mutation rates are about 1x10-6 per locus.
!
How many out of 50 of our gametes has a new mutation somewhere in its genome?
1 in 50
That means about 4% of us (we are diploid), more or less, have a new mutation somewhere in our genomes. Most of these new mutations are silent. YOU could be a mutant.
I can shoot lasers from my eye! Haha!
The only source of new alleles and hence the ultimate source of genetic variation is….
Mutation
What then acts on mutations?
Natural Selection
The allele that codes for a 32 base pair deletion that makes the protein non functional. People with this mutation lack the protein on the surface of their blood cells and homozygous individuals are essentially resistant to HIV
CCR-(delta)32
Did the CCR-32 mutation arise because of HIV?
No! It predates evolution by hundreds or thousands of years and was neutral
the change in allele frequencies that occurs by chance events. In essence, it is identical to the statistical phenomenon of sampling error on an evolutionary scale.
It is a random (stochastic) process.
Genetic Drift
Does the strength of genetic drift get larger or smaller as populations get smaller?
Larger
Does genetic drift generally result in adaptation?
No. There is little effect on large populations with one exception
What is the exception to genetic drift not resulting in adaptation?
It does effect populations over enormous spans of time
When the frequency of an allele reaches 1.0, what is the allele called? This can result in a population becoming homozgous at many loci
Fixed
genetic drift that occurs when a few individuals, representing a fraction of the original allele pool, invade a new area and establish a new population.
Founder Effect
The Amish and the California Cypress a large populations established from a small number of individuals and are therefore examples of
The Founder Effect
periods of very low population size or near extinction. This is another special case of genetic drift.
Bottlenecks
What happens to genetic variation when population ssize is allowed to go very low (when bottlenecks occur?)
Genetic variation is reduced
Cheetahs, Northern Elephant Seals, Ashkenazic Jews, and endangered species are all examples of population that were once in a
Bottleneck
by decreasing genetic diversity, it can put the population at risk of extinction
its random nature increases the genetic differentiation between two or more populations
Genetic Drift
What might occur when one or more populations become reproductively isolated by genetic drift
Speciation
This caused by genetic drift may change the genetic background against which new mutations act. If there is epistasis, a new mutation may be favorable in some populations and unfavorable in others.
Genetic Differentiation
postulates that the interplay between drift and selection are necessary for the origin of certain adaptations.
Wright’s Shifting Balance Theory of evolution
It runs in parallel with Darwinian evolution by natural selection, though its effects are most noticeable and easiest to understand on loci for which there are no differences in fitness between alleles
The Neutral Theory of Molecular Evolution
One of the most interesting breakthroughs in evolutionary biology in the 1960’s-1990’s, has been the development of the neutral theory of molecular evolution.
It was introduced by the Japanese theoretician Motoo Kimura, in the late 1960’s.
It is a theory of evolution that Darwin never could have anticipated (evolutionary biology does not begin and end with Darwin).
The Neutral Theory of Molecular Evolution
It causes change over vast spans of time, at a more-or-less constant rate, when averaged over many loci.
For that reason, it can be used to develop a “molecular clock”..to tell how long it has been since two lineages have diverged.
The Neutral Theory of Molecular Evolution
In the 1960’s techniques of observing genetic variation in natural populations became available, and were pioneered by researchers such as Richard Lewontin.
It was discovered that, in natural populations, many selectively neutral genetic polymorphisms exist.
Kimura based his theory upon this.
The Neutral Theory of Molecular Evolution
He hypothesized that much of genetic variation is actually neutral
Motoo Kimura
He also asserted that most evolutionary change is the result of _______ acting on neutral alleles.
Genetic Drift
New alleles originate through the spontaneous mutatation of a single nucleotide within the sequence of a gene.
In single-celled organisms, or asexuals, this immediately contributes a new allele to the population, and this allele is subject to drift.
The Neutral Theory of Molecular Evolution
In sexually reproducing, multicellular organisms, the nucleotide substitution must arise within the germ line that gives rise to gametes.
The Neutral Theory of Molecular Evolution
Most new alleles are lost due to ______, but occasionally one becomes more common, and by random accident, replaces the original.
The chance of this is small, but over time, it happens occasionally, at a predictable rate.
Genetic Drift
n this way, neutral substitutions tend to accumulate, and genomes tend to evolve.
Many of the polymorphisms we see may be “transient”-one allele is in the process of replacing another.
The Neutral Theory of Molecular Evolution
Is the neutral theory well supported now?
Yes
Do rates of molecular evolution vary among proteins, and among organisms?
Yes. Some proteins allow much less neutral variation, and evolve more slowly.
Is population size important for rates of molecular evolution?
Why?
No.
It cancels out in the math, small populations drift faster, but have fewer mutants per generation
