Honors Bio Chapter 13 Study Guide

UNIT 1

1. What is a population?
  • A population is defined as a group of individuals of the same species that live in the same area and mate to produce fertile offspring.
2. What is a gene pool?
  • A gene pool encompasses all the genes, including all the different alleles for each gene, that are present in a population at any one time.
3. What is allele frequency?
  • Allele frequency refers to the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene.
4. What does natural selection act on?
  • Natural selection acts on the phenotype of an entire organism rather than its genotype.
5. What are the three sources of genetic variation?
  • The three sources of genetic variation include:
      - Mutations
      - Genetic recombination during sexual reproduction
      - Lateral gene transfer
6. What is lateral gene transfer? Give an example.
  • Lateral gene transfer is the passing of genes from one individual to another that is not through offspring, which can occur between individuals of the same species or different species.
      - Example: Many bacteria exchange genes via plasmids, which can lead to antibiotic resistance.
7. What is the difference between a single gene trait and a polygenic trait?
  • Single gene trait: Exhibits 2-3 distinct phenotypes, with phenotype ratios determined by the frequency of alleles in the population and whether the alleles are dominant or recessive.
  • Polygenic trait: Displays many possible genotypes and an even greater variety of phenotypes, which are often not clearly distinct from one another. Typically represented by a bell-shaped curve (normal distribution) of phenotypes.
8. What does the number of phenotypes for a trait depend on?
  • The number of phenotypes for a trait depends on how many genes control that trait.
9. How does the number of phenotypes differ between single gene traits and polygenic traits?
  • Single gene traits have 2-3 distinct phenotypes, while polygenic traits can have many possible genotypes and an even greater variety of phenotypes that are not clearly distinct from each other.
10. What does the distribution of phenotypes for a polygenic trait typically look like?
  • The distribution of phenotypes for a polygenic trait typically resembles a bell-shaped curve.
11. If a single gene trait has two alleles with a simple dominant-recessive pattern how many phenotypes will be in the population?
  • There will be two phenotypes in the population.

UNIT 2

12. What are the FIVE mechanisms of evolution?
  • The five mechanisms of evolution that affect allele frequencies in a population are:
      - Natural Selection
      - Mutation
      - Genetic Drift
      - Gene Flow
      - Non-random Mating
13. For each type of selection (directional, stabilizing, and disruption) give a definition, example, and describe its effect on the distribution curve of traits.

  • Directional Selection:
      - Definition: A form of natural selection in which individuals at one end of a distribution curve have higher fitness than those in the middle or at the other end.
      - Example: Galapagos finches with thicker beaks can eat larger seeds when smaller seeds become scarce. This results in an increase in the average beak size of the population.
      - Effect: The range of phenotypes shifts in one direction.

  • Stabilizing Selection:
      - Definition: A form of natural selection where individuals at the center of a distribution curve have higher fitness than those at either end.
      - Example: In varying seed supplies, birds with extreme beak sizes (very fat or very small) are outcompeted by medium-sized beaks. Over time, the population becomes dominated by medium-sized beaks.
      - Effect: The center of the curve remains the same, but the curve narrows.

  • Disruptive Selection:
      - Definition: A form of natural selection where individuals at both extremes of a distribution curve have higher fitness than those in the middle.
      - Example: When mid-sized seeds become less common, birds with either small or large beaks would have a fitness advantage, causing the population to split into two distinct groups.
      - Effect: The single curve can split into two distinct phenotypes, increasing diversity within the species.

14. What is genetic drift? What types of populations does it occur in?
  • Genetic Drift is defined as a random change in allele frequency due to a series of chance occurrences that can cause an allele to become more or less common in a population. It predominantly occurs in small populations.
15. What is the bottleneck effect?
  • The bottleneck effect refers to a change in allele frequency that follows a dramatic reduction in population size, wherein the surviving population may have a different allele frequency than the original population.
16. What is the founder effect?
  • The founder effect is a change in allele frequencies resulting from the migration of a small subgroup of a population, which establishes a new population with a potentially different allele frequency.
17. What is genetic equilibrium?
  • Genetic equilibrium is the state in which allele frequencies in a population remain constant over time, implying no evolution is occurring.
18. List the FIVE conditions that disturb genetic equilibrium and cause evolution to occur.
  • The five conditions that disrupt genetic equilibrium and contribute to evolutionary changes are:
      - Non-random Mating
      - Small Population Size
      - Gene Flow
      - Mutations
      - Natural Selection
19. When does a population evolve?
  • A population evolves when there are changes in allele frequencies over time through mechanisms of evolution.

UNIT 3

20. What is speciation? What causes it?
  • Speciation is defined as the formation of a new species, which occurs when interbreeding between populations of a species is restricted for any reason.
21. What is reproductive isolation?
  • Reproductive isolation refers to the separation of a species or population in such a way that they no longer interbreed, leading to the evolution of separate species. Changes in the gene pool of one population cannot spread to the other population.
22. For each type of reproductive isolation give a definition AND example: geographic, behavioral, temporal.

  • Behavioral Isolation:
      - Definition: Two populations develop differences in courtship rituals or other behaviors, thereby preventing them from breeding.
      - Example: Eastern and Western meadowlarks have overlapping habitats but do not interbreed because they use different songs to attract mates.

  • Geographic Isolation:
      - Definition: Two populations are separated by geographic barriers, such as rivers, mountains, or bodies of water.
      - Example: A large river may separate squirrels but not birds.

  • Temporal Isolation:
      - Definition: Two populations reproduce at different times.
      - Example: Three similar species of orchids exist in the same rainforest but bloom at different times of the year, preventing pollination between them.

UNIT 4

23. How do genes evolve?
  • Genes evolve through duplication followed by modification of existing genes.
24. How have genomes been affected since genes evolved?
  • The human genome now contains six copies of the gene for beta globin (a polypeptide in hemoglobin), with each copy having mutated differently over time. Gene duplications and rearrangements have markedly increased the size and complexity of eukaryotic genomes.
25. What are Hox genes? How have they led to evolution?
  • Hox genes determine the development of an embryo's body plan, including the formation of arms, legs, and wings, influencing their size and shape. Minor changes in these genes can lead to significant developmental changes and variations in adult body shapes, facilitating evolution.
26. What is a molecular clock? How is it used to determine evolutionary relationships?
  • A molecular clock uses mutation rates in DNA to estimate the time since two species have evolved independently. The greater the differences observed between the DNA of two species, the longer it has been since they shared a common ancestor.
27. Mutations that are of evolutionary significance must occur in what type of cells?
  • Mutations that have evolutionary significance must occur in gametes.