Midterm #2 Flashcards
What is fitness?
The ability of an individual to produce viable offspring and thus pass its alleles along.
Use elephants tusk to describe the difference between genotype, phenotype, and fitness.
Genotype: The genes that are inherited, different alleles for tusk genes contribute to difference amonst shape and size.
Phenotype: The physical manifestation of the gene. The actual size and shape of a tusk in an adult elephant doesn’t depend solely on the products of these tusk alleles. Instead, tusk growth also depends on environmental factors such as the amount and quality of food that the individual got early in life.
Fitness: The likelihood of an allele to continue and be passed on.
What are mutations?
Any change in the base sequence of DNA represents a mutation.
Mutations occur at random and change the genotype creating new alleles.
What is the central dogma of molecular biology?
Genes are made of DNA and that they contain heritable information, which can be passed on to offspring, in code form. The central dogma also states that the information encoded in genes is used to produce RNA and protein molecules that create an individual’s phenotype.
Evolution by the result of natural selection results from what three processes?
- Heritable variation exists in populations. Specifically, in most populations at most times, there are a variety of alleles at every gene. These alleles are created by mutation: random alterations to DNA sequences that can change the information encoded in a gene.
- Not all individuals in a population produce the same amount of viable offspring. In many or most cases, an individual’s reproductive success depends on which alleles it has. Specifically, some alleles lead to higher reproductive success in a particular environment than other alleles. Fitness is defined as the ability to produce viable offspring, so alleles that lead to higher reproductive success are said to have higher fitness.
- Because some alleles lead to more or fewer offspring each generation, the frequencies of alleles will change. This is evolution: a change in the genetic characteristics of a population over time.
Define evolution?
A change in allele frequencies in a population
When does natural selection occur?
When natural selection occurs, alleles that lead to greater fitness increase in frequency and alleles that lead to lower fitness decrease in frequency
When does artificial selection occur?
Humans actively and consciously select which individuals will be the parents of the next generation.
Define adapatation?
A trait the improves fitness
What are the two key impacts that directional selection have on a trait?
- The average changes, because individuals with one extreme have higher fitness while individuals with another extreme have lower fitness. (Think tusks)
- The amount of overall variation decreases, because alleles associated with one extreme are being eliminated.
What is stabilizing selection?
Stabilizing selection on a trait occurs when individuals with the average value have highest fitness and individuals with both extreme phenotypes have lower fitness.
What two impacts does stabilizing selection have on a trait?
1.The average does not change, because individuals with intermediate values of the trait have the highest fitness.
- The amount of overall variation decreases, because alleles associated with both extremes are being eliminated.
Who does genetic drift impact?
Everyone and every population.
What is genetic drift?
Any change in allele frequencies that is due to chance (does not need to impact fitness)
What are two chance events that cause genetic drift?
- Acts on all heritable traits (ones that are not under natural selection)
- Sampling error: Changes in allele frequencies that happen by random chance
How does genetic drift impact alleles?
Drift can lead to the random fixation and loss of alleles. When this happens, it means that genetic drift has reduced genetic variation in populations.
Does genetic drift have a bigger impact smaller or larger populations?
smaller populations
What causes genetic drift?
Genetic drift is mainly caused by luck but can be the result of founder events and bottleneck events
Founder events occur when a relatively small number of individuals disperse to a new habitat and found, or establish, a completely new population.
Bottleneck events occur when a species undergoes a large and rapid decrease in population size due to a disease epidemic, catastrophic storm, or other change.
What occurs during founder events?
Founder events occur when a relatively small number of individuals disperse to a new habitat and found, or establish, a completely new population. Because the founders are a small group, the allele frequencies in the new population are highly unlikely to be identical to the allele frequencies in the original population. The difference in allele frequencies between the two populations is simply due to chance.
Where does genetic drift state that homo sapiens are originally from?
South and east Africa and spread throughout the world
How does genetic drift impact small populations?
One of the major issues is that if the population is small enough, alleles that have low fitness can increase in frequency due to genetic drift. When this happens, populations that are struggling due to habitat loss or other issues can start to struggle due to genetic problems as well.
What is gene flow?
Gene flow causes allele frequencies to change when individuals and their alleles move from one population to join another population.
When gene flow occurs do allele frequencies become more or less similar?
When gene flow occurs between two populations, it makes their allele frequencies more similar. To capture this point, life scientists say that gene flow homogenizes allele frequencies among populations.
What are the fitness effects of gene flow?
Depending on the situation, average fitness in a population can increase, decrease, or stay the same after gene flow occurs. In most cases, though, research has shown that gene flow reduces the average fitness of individuals—meaning that in general, gene flow is a bad thing for the recipient population.
What is a genetic rescue?
Researchers will capture individuals from other populations, transport them, and release them into the struggling population in hopes that the new alleles they contribute will increase genetic diversity and lead to increased average fitness in the threatened population
What consequences does mutation have, in terms of changing allele frequencies and causing evolution?
Mutation is the process that creates new alleles. By creating new alleles, mutation creates genetic variation.
mutation on its own is too rare to create significant changes in the allele frequencies observed in populations.
What is a null model?
A null model specifies the results that should be observed when a process is not occurring. In the case of evolution, the null model specifies what the genotype frequencies will be when none of the four evolutionary processes are impacting allele frequencies at the gene you are interested in
What is the Hardy-Weinberg Principle?
The null model for testing whether or not evolution is occurring. The five assumptions that need to be met are:
1. No assoratative mating
2. Infinite population
3. No mutations
4. No migration
5. No natural selection
What are the genotypes possible in an F1 generation?
There are three genotypes possible in the F1 generation: LL, LS, and SS. The frequencies of these genotypes are p2, pq + pq = 2pq, and q2. These genotype frequencies have to sum to 100%, so p2 + 2pq + q2 = 1.
What is assortative mating?
when individuals choose mates on the basis of having the same or a different phenotype as themselves. In some human cultures, for example, people tend to choose mates with similar cultural, ethnic, physical, or professional traits. This leads to more homozygous phenotypes.
What is inbreeding?
Inbreeding is defined as mating among relatives.
Why Does Non-random Mating Violate the Hardy-Weinberg Principle?
Non-random mating does not change allele frequencies, so it does not cause evolution. It does, however, change genotype frequencies. And it changes them in a specific way: it increases the frequency of homozygotes.
What is the Anthropocene era?
Used to describe the era of human impact on earth.
What is inbreeding depression?
Lowered fitness due to the increased prevalence of homozygous recessive genotypes with deleterious effects.
What occurs during inbreeding depression?
Small populations become inbred. This increases the percentage of individuals with homozygous recessive genotypes, which increases the percentage of individuals expressing the loss-of-function phenotype, which lowers the average fitness of individuals in the population.
What occurs during the extinction vortex?
Once populations get small and/or fragmented due to human activities, the interactions between lack of gene flow and increased impacts from genetic drift, inbreeding, and natural selection make their chances of long-term survival appear slim to none.
What two things can humans do to lessen habitat fragmentation?
- Genetic Rescue
- Wildlife corridors
What is speciation?
The process that creates new types, or species, of organisms. It is a splitting event, where one species breaks into two or more separate species.
What are the two different groups in speciation?
Ancestral Group: The initial group
Daughter Species: Any subsequent groups that form
Why is speciation important?
It creates biodiversity.
What is the mass exctintion?
A current event where humans are altering habitats so profoundly all over the planet that researchers are concluding that a major global extinction event.
What is the only evolutionary function that leads to adaptation?
Natural selection
What are Darwins posulates?
- Phenotypic variation exists within a population.
- Variation is genetically heritable
- Differential reproduction/survival occurs based on that phontypic variation.
What is happening when Darwin’s Postulates are true?
Natural selection is occurring
What is disruptive selection?
Genetic variants that lead to average phenotype become less common in the population over time - selection favours genetic variants that are extremes
What are the four forces/mechanism that drive evolution?
- Natural Selection
- Mutation
- Genetic Drift
- Gene Flow
Do genetic drift and natural selection occur in isolation?
no
What are the two main types of mutations?
- Genetic Mutations: Change small numbers of nucleotides
- Chromosomal Mutations; Change the number o fchromosomes or structure of chromosomes.
What are the three impacts mutations can have in regrads to fitness?
Beneficial, Deleterious, or Neutral
What is allopatric speciation?
Speciation that occurs due to geographical barriers. Gene flow is cut off.
What is sympatric speciation?
Speciation that occurs within individuals in the same place. Temporal variation (different breeding times at day or night)
