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Questions and Answers
What is a primary reason why genetic variation is important in natural selection?
What is a primary reason why genetic variation is important in natural selection?
What does the term 'struggle for existence' refer to in natural selection?
What does the term 'struggle for existence' refer to in natural selection?
Which of the following factors does NOT contribute to the extinction of a species?
Which of the following factors does NOT contribute to the extinction of a species?
Why do organisms over-produce offspring?
Why do organisms over-produce offspring?
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Which reproductive strategy is associated with fungi for increasing their population rapidly?
Which reproductive strategy is associated with fungi for increasing their population rapidly?
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What effect does temperature have on the c^s allele in Siamese cats?
What effect does temperature have on the c^s allele in Siamese cats?
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How did Potentilla glandulosa demonstrate that environment affects phenotype?
How did Potentilla glandulosa demonstrate that environment affects phenotype?
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What happens to Arctic foxes' coats as winter approaches?
What happens to Arctic foxes' coats as winter approaches?
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Which statement is true about human height with respect to genetic inheritance?
Which statement is true about human height with respect to genetic inheritance?
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What is the primary function of the enzyme tyrosinase in Siamese cats and Himalayan rabbits?
What is the primary function of the enzyme tyrosinase in Siamese cats and Himalayan rabbits?
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What is the primary characteristic of stabilising selection?
What is the primary characteristic of stabilising selection?
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How does directional selection affect the mean of a population's phenotype?
How does directional selection affect the mean of a population's phenotype?
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What effect does stabilising selection have in an environment with fluctuating temperatures?
What effect does stabilising selection have in an environment with fluctuating temperatures?
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Which selection type is characterized by favouring individuals with traits that vary in one direction from the mean?
Which selection type is characterized by favouring individuals with traits that vary in one direction from the mean?
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Which scenario exemplifies disruptive selection?
Which scenario exemplifies disruptive selection?
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What is a common outcome of stabilising selection?
What is a common outcome of stabilising selection?
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Which statement describes a gene pool?
Which statement describes a gene pool?
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What is an example of an environmental factor that acts as a selection pressure in a population?
What is an example of an environmental factor that acts as a selection pressure in a population?
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How does natural selection affect allele frequencies in populations?
How does natural selection affect allele frequencies in populations?
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Which type of natural selection favors individuals at both extremes of a trait?
Which type of natural selection favors individuals at both extremes of a trait?
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What is the primary consequence of intraspecific competition in a population?
What is the primary consequence of intraspecific competition in a population?
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Which of the following best defines selection pressure?
Which of the following best defines selection pressure?
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What is a significant outcome of overproduction in a species?
What is a significant outcome of overproduction in a species?
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Which scenario best illustrates stabilizing selection?
Which scenario best illustrates stabilizing selection?
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Which factor is NOT typically considered a selection pressure?
Which factor is NOT typically considered a selection pressure?
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Study Notes
Variation
- Variation refers to the differences between organisms within a species.
- Continuous variation shows a gradual range of phenotypes with no distinct categories. Examples include height and mass in humans.
- Continuous variation is controlled by many genes (polygenes).
- Discontinuous variation shows distinct categories or phenotypes with little overlap. An example is the ABO blood grouping system (A, B, AB, O).
- Discontinuous variation is often controlled by one or a few genes.
Environmental Influences
- Environmental factors determine the expression of a genotype, leading to different phenotypes.
- Examples of environmental influences include diet, temperature, and sunlight.
- These factors affect the overall phenotype without altering the genetic code.
Causes of Variation - Genetic Differences
- Genetic variation results from the genotype (genes and alleles).
- Variations occur among the alleles from one generation to the next due to mutations, crossing over during meiosis, and random assortment of chromosomes.
- Mutations occur if there are errors in the copying of DNA.
- Crossing over during meiosis involves recombination of chromosomes, splitting and recombining of genes and therefore generating new combinations.
Summary Test 17.1
- Continuous variation shows a range, with no distinct separation.
- Discontinuous variation shows distinct categories.
- Polygenes and environmental factors contribute to continuous variations.
- A single gene, or a few, typically control discontinuous variation with less environmental influence.
- Examples of continuous variation in humans include height and mass.
- Examples of discontinuous variation in humans include ABO blood groups.
- A change in DNA sequence is known as a gene mutation.
- Crossing over during meiosis results in recombinants.
The t-test
- The t-test is used to determine if the difference in mean values between two sets of continuous data is significant or due to chance.
- The test requires data from a normally distributed population.
- Standard deviations should be similar.
- Each sample should contain less than 30 values.
- The equation involves mean, standard deviation, and sample sizes to obtain degrees of freedom.
Calculating the standard deviation
- The formula for standard deviation involves summing the squared deviations from the mean, dividing by the number of values minus one, then taking the square root.
- The steps are:
- Find the mean of the values.
- Subtract the mean from each value.
- Square each of the differences.
- Sum the squared differences.
- Divide this sum by the number of values minus one.
- Take the square root of the result to find standard deviation.
Natural Selection
- Natural selection is where better-adapted organisms are more likely to survive and pass on their genes.
- Populations produce more offspring than can be supported by resources, resulting in competition.
- Individuals with advantageous traits are more likely to survive and reproduce (survival of the fittest).
- Beneficial alleles become more frequent in the population over time.
- Examples of natural selection include antibiotic resistance in bacteria and industrial melanism in peppered moths.
Environmental and Phenotype
- Organisms' phenotypic expression is influenced by the environment, not just their genes.
- Environmental examples include Siamese cats (temperature affects fur colour), Arctic foxes (temperature affects fur colour) and plants growing at different altitudes.
- Genotypes provide a blueprint for development, while the environment determines expression within limits of the blueprint.
Causes of Extinction
- Climate change, habitat loss, competition from other species (including humans), overhunting.
- Extinction is a natural process but often accelerated by human activities.
Allele Frequencies
- A gene pool is the complete set of alleles in a population at a given time.
- Allelic frequency describes how often an allele occurs in the gene pool.
- The Hardy-Weinberg principle describes conditions where allele frequencies remain constant from one generation to the next (no mutations, no selection, large population, random mating, no gene flow).
Processes Affecting Allele Frequencies
- Selection pressure and the founder effect are two processes that can alter allele frequencies in populations.
- Selection pressures favor certain traits. An example is how in a malarial area, individuals with sickle cell trait (heterozygous) have an advantage.
- Founder effect occurs when a small group colonizes a new region. This group carries only a fraction of the original population's genetic diversity.
Isolation Mechanisms and Speciation
- Speciation is the formation of new species.
- Species are groups of organisms that can interbreed naturally to produce fertile offspring.
- Isolation mechanisms prevent gene flow between populations (e.g., geographic, ecological, behavioral isolation).
- Allopatric speciation occurs because of geographical barriers.
- Sympatric speciation occurs without geographical barriers.
Selective Breeding
- Selective breeding, or artificial selection, is the selection of individuals with desired traits to reproduce and pass their genes to the next generation.
- This method reduces genetic diversity.
- Examples are improvements of milk yield in dairy cattle.
- Examples include crops that are disease resistant and have higher yields.
Crop Improvement
- Improving crop yield involves selecting varieties with advantageous traits and continuously breeding them with the same traits for generations.
- This process can lead to characteristics like disease resistance, higher yields, and better quality produce.
- Introduction of disease resistance and gibberellin synthesis are examples.
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Description
Test your understanding of natural selection and genetic variation with this comprehensive quiz. Explore concepts like the struggle for existence, reproductive strategies, and the effects of temperature on phenotypes. Challenge yourself with questions that delve into the science of evolution and adaptation.
