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Unity and diversity - Evolution and speciation

Grade 11IBBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Evolution is defined as the cumulative change in the heritable characteristics of a population over time. These changes are passed down through genes.

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Natural Selection is the primary mechanism of evolution. It requires variation within a species, which is produced by mutation, meiosis (crossing over and independent assortment), and sexual reproduction.

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Adaptive Radiation occurs when a single ancestral species evolves into several different species that occupy different ecological niches. A classic example is the pentadactyl limb, a homologous structure found in amphibians, reptiles, birds, and mammals.

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Speciation is the process by which new species are formed. This occurs when populations of the same species become reproductively isolated, meaning they can no longer interbreed to produce fertile offspring.

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Isolation mechanisms include: 1. Geographic isolation (Allopatric speciation), 2. Behavioral isolation (Sympatric), and 3. Temporal isolation (Sympatric).

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Evidence for evolution includes the fossil record (showing transitions), selective breeding of domesticated animals, and molecular evidence (DNA and protein sequences).

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Cladistics uses shared derived characteristics to establish evolutionary relationships. A clade is a group of organisms that have evolved from a common ancestor.

📐Formulae

p+q=1p + q = 1

p2+2pq+q2=1p^2 + 2pq + q^2 = 1

💡Examples

Problem 1:

In a certain population of beetles, the allele for black wing color (BB) is completely dominant over the allele for green wing color (bb). If 9%9\% of the population is green, calculate the frequency of the dominant allele (pp) and the percentage of the population that is heterozygous (2pq2pq), assuming the population is in Hardy-Weinberg equilibrium.

Solution:

  1. Identify the frequency of the homozygous recessive genotype (q2q^2): q2=0.09q^2 = 0.09.
  2. Calculate the frequency of the recessive allele (qq): q=0.09=0.3q = \sqrt{0.09} = 0.3.
  3. Calculate the frequency of the dominant allele (pp): p=1−q=1−0.3=0.7p = 1 - q = 1 - 0.3 = 0.7.
  4. Calculate the frequency of the heterozygotes (2pq2pq): 2pq=2×0.7×0.3=0.422pq = 2 \times 0.7 \times 0.3 = 0.42.
  5. Convert to percentage: 0.42×100=42%0.42 \times 100 = 42\%.

Explanation:

The frequency of the dominant allele pp is 0.70.7. Since 42%42\% of the population carries the BbBb genotype, they will appear black but carry the green allele.

Problem 2:

Explain how the evolution of antibiotic resistance in bacteria serves as an example of natural selection.

Solution:

  1. Variation exists in a bacterial population; some bacteria have a mutation providing resistance to an antibiotic.
  2. When the antibiotic is applied, the non-resistant bacteria are killed (SelectionPressureSelection Pressure).
  3. The resistant bacteria survive and reproduce, passing the resistance gene to the next generation via binary fission or horizontal gene transfer.
  4. Over time, the frequency of the resistant allele increases in the population.

Explanation:

This demonstrates a rapid evolutionary change driven by environmental pressure (the antibiotic), leading to a population better adapted to the environment.