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.
