Chapter 14 - Microevolution/Population Evolution Flashcards
Does natural selection act on individuals?
Yes, natural selection acts on individuals. (but that’s not the same as evolution which acts on the level of populations!!)
Can the evolutionary impact of natural selection be seen on the individual level?
No. It’s apparent only in the changes seen in a population of organisms over generations.
What is a population?
A group of individuals of the same species, in the same area that produce fertile offspring.
Evolution can be measured as…
…a change in the prevalence of certain heritable traits in a population over a number of generations.
What is microevolution?
Microevolution can be measured as…
Evolution on the smallest scale (just looking at one population of a species).
…a change in allele frequency in a population over time.
What is macroevolution?
Evolutionary change above the species level including the origin of new taxonomic groups, adaptive radiation, and mass extinction.
What is a gene pool?
The total collection of genes in a population at one time. All of the alleles in all of the individuals within the population.
Where do new alleles come from?
New alleles originate by mutation, which is a change in the nucleotide sequence of DNA.
Can all types of cells pass their mutations on to offspring?
No, only mutations in cells that produce gametes can be passed onto offspring.
Are random mutation usually beneficial to organisms?
No, but on rare occasions, you can win the “genetic lottery” or the environment can change so a mutation becomes favourable.
What type of error in meiosis can provide an important source of genetic variation?
Duplication of small pieces of DNA.
Why are we more likely to see mutations in prokaryotes?
Because they multiply so rapidly AND because they are haploid.
What is the average mutation rate in plants and animals?
1 in every 100,000 genes per generation.
What prevents most mutations from notably affecting genetic variation in plants and animals (3 factors)?
Low mutation rates, long generation times, and having a diploid genome.
Which parts of meiosis function to
increase genetic variability within a population (3)?
Independent assortment.
Crossing over in prophase 1.
Random fertilization of gametes.
What is the ultimate source of genetic variability that makes evolution possible?
MUTATION!!!!!
What is the Hardy-Weinberg equation used for?
To test whether a population is evolving.
What is the Hardy-Weinberg principle?
Genetic variation is necessary for a population to evolve, but does not guarantee that it will.
Using the H-W equation, we know a population is NOT evolving when…
… the frequency of each allele remains the same from generation to generation.
In the Hardy-Weinberg equation, which letters are used to represent dominant and recessive alleles?
p = Dominant allele
q = Recessive allele
What two equations are used in the Hardy-Weinberg principle? What do the different parts represent?
p + q = 1
p² + 2pq + q² = 1
A gene has two alleles A and a
Frequency of allele A = p
Frequency of allele a = q
* remember to account for organisms being diploid!
Frequency of genotype AA = p²
Frequency of genotype Aa = 2pq
Frequency of genotype aa = q²
In a H-W example, how do we find out the allele frequency for the next generation?
By plugging the parent frequencies into a heterozygous x heterozygous Punnett square or the H-W equation.
Review notes/slide for details.
A population is in H-W Equilibrium when… (5 conditions).
How often does this happen in real life?
- The population is very large (no genetic drift);
- There is no gene flow between populations;
- There are no mutations;
- Mating is completely random;
- There is no natural selection.
Rarely, if ever.
What are the 3 main causes of evolutionary change/mechanisms of microevolution?
Natural selection, genetic drift, and gene flow (because mutations on their own are uncommon and change allele frequencies very slowly).
What is genetic drift?
When chance events cause allele frequencies to fluctuate unpredictably from one generation to the next. The smaller the population the greater the effect.
What two types of genetic drift did we talk about?
The bottleneck effect and the founder effect.
What is the bottleneck effect? How does it impact the alleles in a gene pool?
When catastrophes kill large numbers of individuals, leaving a small surviving population with a different a genetic makeup. Usually reduces the number of alleles within the gene pool.
What is the founder effect?
Genetic drift likely to occur when a few individuals colonize an island or new habitat. The colonizing group could have a very different ratio of alleles than the population they left.
What is gene flow?
When a population gains or loses alleles when fertile individuals or their gametes (i.e. tree pollen) migrate.
What is the ONLY mechanism/ means of microevolution that leads to adaptive evolution? Why?
Natural selection because it combines chance AND sorting. By consistently favouring some alleles over others, natural selection works to improve the match of an organism with its environment.
What is relative fitness?
The contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
More fit = more viable offspring.
What are the three ways natural selection can alter populations?
Stabilizing, directional or disruptive.
What is stabilizing selection?
Selection favours intermediate phenotypes (the mid point in a range of phenotypes). Reduces variation and maintains the status quo for a particular trait.
What is directional selection? When is it most common?
Selective pressure against one of the phenotypic extremes (all phenotypes shift away from this extreme). Most common during periods of change or when species migrate to a new habitat.
What is disruptive selection?
Extremes are favoured over intermediate phenotypes. It’s like the opposite of stabilizing selection.
What is sexual selection? What are the two types
Selection surrounding reproduction where individuals with certain traits are more likely than others to obtain mates. Inter and intra sexual selection
What is sexual dimorphism?
A difference in appearance between males and females of the same species.
What is inter sexual selection?
Selection between opposite sexes.
Females may be choosy when selecting their mates, so not every male has the same opportunity to pass on their genes.
What is intra sexual selection.
Selection within the same sex, usually between males. i.e. physical fighting or other competitions to obtain breeding rights.
Why aren’t recessive traits eliminated/How does being diploid help maintain genetic variation?
Recessive alleles are only subject to natural selection in homozygous recessive individuals. Heterozygous individuals can keep these alleles, which maintains a larger gene pool.
Why can’t natural selection make perfect organisms (4)?
- It has to work with existing alleles.
- It’s descent with modification,
not working from scratch. - Adaptations are often compromises.
- Chance plays a large role than so sometimes beneficial alleles may be lost.
Does an evolutionary trend imply that evolution is goal oriented?
No, evolution is just the result of interactions between organisms and their current environment.
