18 Questions
What is the smallest unit of evolution?
Population
What happened to the average beak size in the finch population after the 1977 drought?
It increased
What is the effect of a bottleneck on genetic variation in a population?
A decrease in genetic variation
What type of change in allele frequencies occurred in the finch population after the 1977 drought?
Directional change
What is the primary mechanism that drives adaptive evolution in a population?
Natural selection
What is the importance of genetic drift in conservation biology?
It decreases genetic variation
What did not occur in the individual finches during the 1977 drought?
An evolution of larger beaks
What is the result of birds with large beaks being better able to survive and reproduce during a drought?
An increase in the proportion of birds with large beaks in the population
What is the term for the change in allele frequencies in a population over time?
Microevolution
Which mechanism of evolution can lead to a loss of allelic variation in a population?
Genetic drift
What is the process that can introduce new alleles into a population from other populations?
Gene flow
What is the key concept that was missing from Charles Darwin's explanation of evolution?
The concept of inheritance
What is the primary reason why the change in allele frequencies from one generation to the next is very small?
Mutations are rare.
What is the effect of nonrandom mating on allele frequencies in a gene pool?
It has no effect on allele frequencies.
What is the primary mechanism by which natural selection alters allele frequencies?
Differential reproductive success.
What is the effect of genetic drift on the genetic variation of a population?
It reduces the genetic variation of a population.
What is the primary mechanism by which new alleles can enter a population?
Gene flow from other populations.
What is the significance of the increased frequency of the DDT-resistance allele in Drosophila melanogaster?
It is an example of natural selection.
Study Notes
The Evolution of Populations
- A common misconception about evolution is that organisms evolve during their lifetimes, but it is the population that evolves, not the individual.
- Natural selection acts on individuals, affecting their survival and reproductive success relative to others in the population.
The Medium Ground Finch Example
- In 1977, a drought on the Galápagos Islands affected the medium ground finch (Geospiza fortis) population, with only 180 out of 1200 birds surviving.
- The surviving finches had larger, deeper beaks than those that died, allowing them to crack open large, hard seeds that were abundant during the drought.
- After the drought, the average beak size in the population was larger, demonstrating evolution by natural selection.
Microevolution and Mechanisms of Change
- Microevolution is defined as a change in allele frequencies in a population over time.
- Three mechanisms can cause allele frequencies to change: natural selection, genetic drift, and gene flow.
- Natural selection is the only mechanism of adaptive evolution, improving the match between organisms and their environment.
Genetic Variation and Evolution
- Mutation and sexual reproduction produce the genetic variation that makes evolution possible.
- Charles Darwin proposed a mechanism for change in species over time, but lacked an understanding of inheritance that could explain how chance variations arise in a population.
- Gregor Mendel's particulate hypothesis of inheritance supported Darwin's theory, stating that parents pass on discrete heritable units (genes) that retain their identities in offspring.
Mechanisms of Evolutionary Change
- New mutations can modify allele frequencies, but the change is small because mutations are rare.
- Nonrandom mating can affect the frequencies of homozygous and heterozygous genotypes, but has no effect on allele frequencies in the gene pool.
- Natural selection, genetic drift, and gene flow are the three mechanisms that directly alter allele frequencies, leading to evolutionary change.
Natural Selection
- Individuals in a population vary in their heritable traits.
- Individuals with variations better suited to the environment tend to produce more offspring than those with less suitable variations.
- As a result of selection, alleles are passed on to the next generation in frequencies different from their relative frequencies in the present population.
- For example, the fruit fly Drosophila melanogaster developed an allele conferring resistance to insecticides, which increased in frequency from 0% to 37% over 20 years of DDT use.
Learn about microevolution, the change in allele frequencies in a population over time, and its mechanisms, including natural selection, genetic drift, and gene flow. Understand how these processes shape the characteristics of a population.
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