Flashcards in Final Exam Review Deck (48)
What is evolution?
A change in allele frequencies in a population over time
Does NOT require a change in species
Does NOT indicate why allele frequencies have changed
Occurs in populations, NOT individuals
Requires genetic variation to act on , which comes from mutations that generate new alleles
What are the mechanisms of evolution?
1. Selection (Artificial, Natural, Sexual)- Process by which allele frequencies change due to differential reproduction
2. Genetic Drift
3. Migration- When new individuals enter a population from another population and may bring different alleles
**All can cause allele frequencies to change
What is heritability (h2) and how is it measured?
Proportion of a population's phenotypic variation controlled by genetic rather than environmental factors
Slope of regression line between mean parent and offspring values for a trait
VP= VG + VE
How do the different forms of selection differ from each other? How are they the same?
All forms of selection share 2 variables:
1) Heritable variation among individuals
2) Differences among individuals in number of surviving offspring
Artificial- Humans choose which individuals pass on alleles; Some alleles become more common because of selective breeding
Natural- Nature decides which individuals reproduce most; Different environments select for different traits depending on major causes of death; Results in ADAPTATIONS; NOT goal-oriented; Can be fast or slow, depends on how much advantage trait provides; Does not create new traits, but eliminates old ones if a better one exists
Sexual- individuals who are better at obtaining mates reproduce more (2 components- female mate choice and male competition)
What is fitness?
# of copies of an individual's genes that get passed on to future generations
Good indicator is number of surviving children and grandchildren
What are adaptations?
Traits that help an organism survive and reproduce in a particular environment
Favored by selection
How do the following provide evidence of evolution: fossils, homology, vestigial
traits, biogeography, the universality of the genetic code, ERVs?
All demonstrate change over time and common ancestry and support each other
Fossils- Mere existence does NOT provide evidence for evolution; but, the fossil record does; Organisms are found in historical sequence; Fossils demonstrate a gradual transition among forms
Homology- Similarities in structure among organisms, as is predicted if they arose from the same common ancestor
Vestigial traits- Structures that have no apparent purpose, but are carry-overs from ancestral species
Biogeography- Observations: Many island species are endemic; endemic species on islands are similar to species on nearest mainland; species found on nearby islands are similar to each other; Best explanation: the island species evolved from populations that were begun by individuals from the mainland; This is the pattern predicted by common ancestry
Universality of genetic code- All living organisms have the same system for building proteins, which is STRONG evidence that all life shares a common ancestor
ERVs- Inactive viral sequences embedded in the genome; Remnants of past infections; Patterns of shared ERVs correspond to hypothesized phylogenies, as would be predicted by common ancestry
What is a scientific theory?
A big explanatory idea
Broad-ranging; pulls together diverse observations
Testable; allows predictions about future observations; conforms to laws of chemistry and physics; open to revision
What criteria must be met for an explanation to be considered scientific?
1) Be testable
2) Conform to the laws of chemistry and physics (be natural, not supernatural)
Open to revision
What is the significance of Hardy-Weinberg Equilibrium?
Dominant alleles do not automatically spread: there needs to be an evolutionary mechanism to cause an allele to spread
We can analyze populations to identify genes that are evolving
There is no evolution in the absence of an evolutionary mechanism
Allele frequencies are inherently stable unless there are pertubations
What were the important trends in human evolution?
Human and chimp lineages diverged about 6 mya
Many different hominin species have existed, often simultaneously
Human family tree is a twiggy bush rather than a linear progression
Few older hominin fossils have been found because they died in forests that do not fossilize well and are hard to find fossils in
1st bipeds (walk on 2 legs) appeared early in hominin evolution (advantage= can see farther, keep cooler, carry food, and better for long-distance travel)
1st manufactured stone tools about 2 mya
Fire about .5 mya
What is the relationship between humans and chimpanzees?
Humans and chimps share a recent common ancestor that lived about 6 million years ago
What are the different forms of symbiosis?
1. Mutualism- a symbiosis in which both organisms benefit (bee and flower)
2. Commensalism- a symbiosis in which one organism benefits without helping or harming the other (Clown fish and anemone)
3. Parasitism- a symbiosis in which one organism benefits at the expense of the other (humans and tapeworms)
How do organisms optimize offspring size and number?
Optimizing size vs number of offspring
Larger offspring typically have higher survival, but fewer can be produced
Solution: produce offspring of size that yields the greatest number of survivors
Multiply number by survival probability for each size
How are population sizes estimated in the field?
Mark and recapture studies
1. Capture sample of animals and mark them
2. Release marked animals
3. Later date: capture new sample
4. Use the proportion of marked animals that were recaught to estimate total population size
Marked(1)/Pop. size= recaught marked (2)/Total caught (2)
What is an age structure diagram and how is it used?
Description of what % of population is of reproductive vs prereproductive age
Generates prediction of how population size will change in the future
Width of segment represents percent of population in that age bracket
What is a survivorship curve and what does it tell you about a population?
Represents probability of survival relative to stage of life
1. Convex 2. Constant 3. Concave
% surviving vs. % max lifespan
How do we use a life table to determine life expectancies and survivorship curves?
Give a systematic picture of age specific mortality and survival
What is intrinsic rate of increase (r)?
Population growth rate for a population with unlimited resources
Larger organisms have smaller Rmax values
What is carrying capacity (k)?
The maximum number of individuals that an environment can sustainably support
What is environmental resistance?
Factors that limit population growth
Maintain populations at or below carrying capacity
Two categories: density-dependent and density-independent
What is the difference between density-dependent and density-independent effects
on population growth?
Dependent- Limit population growth as density increases by decreasing the birth rate and or increasing the death rate; Can cause population to stabilize or decline
Intraspecific competition (within species)-reduces individual growth rate and reproduction
Disease/parasites- spread easily as pop. density increases
Predation- as prey increase, supports larger population of predators
Food, light, space
Affect population size regardless of density
What are the trends in human population growth?
Growth rate for humans is 1.1%
Majority in less developed countries
Past increases in human pop. size were associated with increases in carrying capacity
Has been a decline in pop growth RATE since 1960s
Increases in carrying capacity with tool-making and industrial revolutions
What is the competitive exclusion principle?
No 2 species can have exactly the same niche
2 species that compete for the same resources cannot steadily coexist.
One species will outcompete the other
What is resource partitioning?
How species avoid niche overlap
The use of slightly different niches to minimize competition
Examples: different species of warblers live in different areas of same trees, different root morphologies in plants, finches eat different foods, hawks and owls are active at different times of day, frogs breed at different times of the year
How do we interpret the zero-growth isoclines for competing populations?
For analysis of interspecific competition
Mathematical representation of competitive exclusion principle
How do predator-prey cycles work?
The 2 populations limit each other's density
Prey pop limited by predation and predator pop limited by prey availability
Many infectious diseases also follow cycle pattern if the disease can only be contracted once
What is coevolution?
2 species evolve together and have specific adaptations for dealing with each other
Like an arms race, because 2 sides go back and forth putting pressure on one another to get better
Can lead to extreme adaptations for both
What is genetic drift (incl. bottleneck and founder effects)?
Any change in allele frequencies due to chance, especially important in small populations where alleles are easily lost
Founder effect= a few individuals start a new population, but new population usually only contains a subset of alleles from parent population
Bottleneck effect= a catastrophic event reduces the population to a small size and survivors are unlikely to carry all alleles from original population