Chapter 20 ch 1 Flashcards
evolutionary theory
was created by Charles darwin
used by humans to vaccines
Charles Darwin year: 1831
5 year voyage on the H.M.S. Beagle around the world to study oceans and collect biological info
Natural Selection
slight variations among individuals affect chances for survival and production of offspring
theory of evolutionary change (def)
- Species change over time. Groups of organisms change (what they eat, where they live, the numbers of them with a certain trait etc)
- Species all share common traits, but the size and things may change.
- Process of this change is natural selection
* populations evolve
if they are evolutionarily successful,
can they reproduce? Are they surviving?
Population
a group of individuals of the same species that live and interbreed in a particular geographic area at the same time
Adaptation meaning
The process by which characteristics that are useful evolve
The characteristics themselves – something that has helped an organism adjust to conditions in an environment
*organism has adapted when scientists can demonstrate that some organisms survived the event better than others
Charles Darwin year 1866
Mendel publishes his paper of pea genetics (dominant and recessive traits)
Charles Darwin year 1900-1918
Basic principles of inheritance genetics established
Charles Darwin year 1947-1960
Emphasis on chromosomal evolution, models of speciation, geographic variation, population genetics
Charles Darwin year 1970(?)
Intro of molecular variation, phylogenetic analysis, sexual selection, behavior
Charles Darwin year 1980-present
Exponential increase in studies of molecular evolution and developmental processes of evolution
Sexual selection
introduced by Darwin, is that there are specific traits that organisms use to choose traits like Nice feathers, etc.
Heritable genetic variation:
potential for change because there is some variation from your parents that you received
ie. phenotype
phenotype
the physical expression of an organisms genes (characteristics like eye color, hair color)
trait
Specific forms of a characteristic (brown eyes)
Heritable trait
form of a characteristic at least partly determined by genes
genotype
genetic makeup of an organism. This is like Aa,
There must be differences in the genotypes as certain genotypes are more present than others therefore adaptations
population genetics’ three main goals
Explain origin and maintenance of a genetic variation
Explain the patterns and organization of genetic variation
Understand the mechanisms that cause changes in allele frequencies in populations
alleles
different forms of a specific gene
Gene pool
sum of all copies of all alleles at all loci in a population
two tenants of evolution
Survival and reproduction
Allele frequency
the proportion of a given allele or genotype in a gene pool at a particular locus
p and q
allelic frequencies
(P +Q)^2
phenotypic frequencies
P^2, 2pq, q^2
genotypic frequencies
5 restrictions on hardy equilibrium
- No mutations must occur so that new alleles do not enter the population.
- No gene flow can occur (i.e. no immigration/emigration of individuals into, or out of, the population).
- Random mating must occur (i.e. individuals must pair by chance)
- The population must be large so that no genetic drift (random chance) can cause the allele frequencies to change.
- No natural selection can occur so that certain alleles are not selected for, or against.
p can be calculated by
number of copies of the allele in the population OVER sum of all alleles in the population
polymorphic
multiple alleles
monomorphic
has one allele and frequency is one
calculating allelic frequencies (Conant)
add up all the allele ASK PEOPLE
When the value isn’t 1 in hardy weinberg
Important for predicting the approximate genotype frequencies of a population
Can show which mechanisms of evolution are acting on a population by how it is deviating from H-W equilibrium
Consequences of ideal conditions of hardy Weinberg:
Frequencies of alleles at a locus remain constant from generation to generation
Following one generation of random mating the genotype frequencies occur in the following proportions:
mutations (The Mechanisms of Evolution)
Any change in an organism’s DNA
Appear to be random
Harmful or neutral changes may become advantageous over time
Can restore alleles to populations that have been lost
Mutation rates low for most loci (one in a million)
Gene flow (The Mechanisms of Evolution)
Migration of individuals of similar species from other populations
Relatively common
May add new alleles to gene pool
May change frequency of alleles
Genetic drift (The Mechanisms of Evolution)
Random changes in allele frequencies
Harmful alleles may increase, advantageous alleles may be lost
Population bottlenecks (The Mechanisms of Evolution)
large populations go through large loss of numbers,
genetic variation may be lost
usually followed by founder effect: new individuals populate a new region bringing new alleles, change in genetic variation, often found after bottleneck
Non-random mating (The Mechanisms of Evolution)
Choosing particular genotypes as mates, homozygous genotypes overrepresented
includes self-fertilization
fitness (Mechanisms of Evolutionary Change)
the reproductive contribution of a phenotype to subsequent generations relative to the contributions of other phenotypes
Determined by the average rates of survival and reproduction of individuals with
a certain phenotype
natural selection results are
variable – most advantageous characteristics are influenced by multiple alleles and genetic variations
Stabilizing selection (Mechanisms of Evolutionary Change)
favors average characteristics/individuals (human height, birth weights)
Reduces variations in populations without
changing mean values
- most common
Directional selection (Mechanisms of Evolutionary Change)
favors individuals that vary in one direction from the mean of population
If apparent in multiple generations an
evolutionary trend is seen (toxin resistance
in snakes, Texas Longhorns)
Disruptive selection (Mechanisms of Evolutionary Change)
– favors individuals that vary in opposite directions from mean of population
Bimodal distribution of a phenotype (black
-bellied seedcracker)
Sexual selection (Mechanisms of Evolutionary Change)
acts on characteristics that determine reproductive success
Darwins’s explanation for the evolution of apparently useless characteristics
(bright colors, long tail, horns, antlers, elaborate courtship displays)
These features either improved the ability to compete for access to mates or
made bearers more attractive to mates
characteristics may indicate increased, health, reproductive fitness
Neutral alleles (How is Genetic Variation Maintained?)
an allele that is no better or worse than alternative alleles at the same locus
Tend to accumulate in a population over time providing genetic variation
Sexual recombination (How is Genetic Variation Maintained?)
generates an endless variety of genotypic combinations
increases the evolutionary potential of a population
Gives more variability (good evolutionarily)
Frequency-dependent selection (How is Genetic Variation Maintained?)
the maintenance of a polymorphism when the fitness of a genotype depends on its frequency in a population (scale eating fish)
- more polymorphism usually means that more organisms are going to survive
- Having different organisms have different characteristics (ie breeding in June vs october) helps keep population alive
- Having different coloured body parts stops predation etc.
- Multiple genotypes in the population help maintain the species as a whole
Environmental variation (How is Genetic Variation Maintained?)
no single genotype performs well in all environmental conditions
Favors genetic variation
Geographically distinct subpopulations (How is Genetic Variation Maintained?)
subject to different selective pressures in different environments and areas
Developmental processes (Constraints on Evolution)
we build on what we already have. If there are new structures and reproductive ways, it was built on the basis of what was already there
Means that evolution takes a long time
may sacrifice one ability to gain another
Trade-offs (Constraints on Evolution)
fitness benefits must outweigh fitness costs
Maintaining features may be energetically costly, lifespan may be shorter
Short-term and long-term outcomes may differ (Constraints on Evolution)
it is not always known how a short-term noticeable evolutionary feature will fare in the future
How evolutionary processes act may change over time
different lineages may evolve in different directions
how have humans influenced evolution?
Reduced loss of life due to predators, bad weather
Increased loss of life due to disease, accidents, war, murder
Control of species we consider “pests”
name some mechanisms of evolutionary change
gene flow etc.
what result in adaptation?
any selections
how is genetic variation maintained in populations?
types of variations
contraints on evolution?
long term, fitness, structure etc.
Natural selection vs adaptation
natural selection is what a pressure selects for
Population has adapted when it survives the pressure
Adaptation is a response to selective pressure
most likely to result in adaptation?
directional selection
