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Biology: Genetics, Reproduction, and Biotechnology - Evolution, Natural Selection, Speciation, and Evidence for Evolution

Grade 8IB

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

🔑Concepts

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Evolution is the cumulative change in the heritable characteristics of a population over time. It is driven by the process of Natural Selection, which acts on the phenotype of organisms.

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Natural Selection occurs through four main steps: Variation (genetic differences due to mutation/meiosis), Overproduction (more offspring than environment can support), Selection (differential survival and reproduction), and Adaptation (favorable alleles becoming more common).

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Evidence for evolution includes the Fossil Record (showing transitional forms), Comparative Anatomy (Homologous structures like the pentadactyl limb), and Molecular Biology (similarities in DNA sequences).

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Speciation is the formation of new and distinct species in the course of evolution. This typically occurs via geographical or reproductive isolation, preventing gene flow between populations.

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Artificial Selection (Selective Breeding) is a human-driven process where specific traits are chosen, providing evidence that populations can change significantly over generations.

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The concept of 'Survival of the Fittest' describes the reproductive success of an organism; fitness is measured by the contribution an individual makes to the gene pool of the next generation.

📐Formulae

p+q=1p + q = 1

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

R=ΔGΔtR = \frac{{\Delta G}}{{\Delta t}}

I=faft×100I = \frac{{f_a}}{{f_t}} \times 100

💡Examples

Problem 1:

In a population of beetles, the frequency of the dominant allele for color (AA) is p=0.7p = 0.7. Calculate the frequency of the recessive allele (aa), denoted as qq.

Solution:

Using the formula p+q=1p + q = 1, we substitute the known value: 0.7+q=10.7 + q = 1 q=1−0.7q = 1 - 0.7 q=0.3q = 0.3

Explanation:

In population genetics, the sum of the frequencies of all alleles for a particular gene must equal 11 (or 100%100\%).

Problem 2:

Explain the evolution of Antibiotic Resistance in bacteria using the principles of natural selection.

Solution:

  1. Variation: A population of bacteria has a mutation that provides resistance to an antibiotic. 2. Selection: When the antibiotic is applied, non-resistant bacteria die. 3. Reproduction: The resistant bacteria survive and reproduce via binary fission. 4. Frequency: The frequency of the resistance allele increases in the population over time.

Explanation:

This is an example of 'Directional Selection' where an extreme phenotype (resistance) is favored by environmental pressure.

Problem 3:

Calculate the percentage of heterozygous individuals (2pq2pq) in a population where the frequency of the recessive allele is q=0.4q = 0.4.

Solution:

First, find pp: p=1−q=1−0.4=0.6p = 1 - q = 1 - 0.4 = 0.6 Next, calculate 2pq2pq: 2×0.6×0.4=0.482 \times 0.6 \times 0.4 = 0.48 Percentage: 0.48×100=48%0.48 \times 100 = 48\%

Explanation:

The Hardy-Weinberg equation allows us to predict the genotype frequencies in a population based on allele frequencies.

Evolution, Natural Selection, Speciation, and Evidence for Evolution Grade 8 Notes & Examples