Natural and artificial
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Explain how a population's capacity to produce many offspring contributes to natural selection.
Overproduction leads to competition for limited resources. This 'struggle for existence' results in individuals with advantageous adaptations being more likely to survive, reproduce, and pass on their alleles, driving natural selection.
Describe how directional selection affects allele frequencies in a population.
Directional selection favors one extreme phenotype, causing a shift in the population's allele frequencies over time. Alleles contributing to the favored phenotype become more common, while those linked to the opposite extreme become less frequent.
Define the founder effect and explain its impact on allele frequencies.
The founder effect occurs when a small group of individuals establishes a new population, carrying only a subset of the original population's genetic diversity. This can lead to altered allele frequencies in the new population compared to the original, potentially reducing genetic variation.
Outline how genetic drift, specifically the bottleneck effect, can alter allele frequencies in a population.
The bottleneck effect occurs when a population undergoes a drastic reduction in size, often due to a catastrophic event. The surviving individuals may not represent the original population's genetic diversity, leading to random changes in allele frequencies and reduced genetic variation.
Describe the mechanism by which bacteria become resistant to antibiotics.
Random mutations can arise in bacteria, some conferring resistance to antibiotics. In the presence of antibiotics, susceptible bacteria die, while resistant bacteria survive and reproduce. This leads to a rapid increase in the frequency of antibiotic resistance alleles within the bacterial population due to natural selection.
State the conditions under which the Hardy-Weinberg principle can be applied.
The Hardy-Weinberg principle applies when: 1) There is no mutation, 2) There is random mating, 3) There is no gene flow, 4) There is no natural selection, and 5) The population size is large (no genetic drift).
Describe the principles of selective breeding (artificial selection).
Selective breeding involves humans selecting individuals with desirable traits to breed, aiming to enhance these traits in subsequent generations. This process can lead to significant changes in a population's characteristics over time, but reduces genetic diversity and can lead to inbreeding.
Give an example of selective breeding for disease resistance in plants.
Varieties of wheat and rice have been selectively bred to introduce genes conferring resistance to specific fungal or viral diseases. This process involves crossing plants with resistance genes with high-yielding varieties, selecting for offspring that combine both traits.
Explain how inbreeding and hybridization are used in maize breeding.
Inbreeding is used to create homozygous lines in maize, leading to uniform traits but reduced vigor. Hybridization then crosses these inbred lines to create F1 hybrids, which exhibit hybrid vigor (increased yield and robustness) due to the masking of deleterious recessive alleles.
Outline the process of selective breeding to improve milk yield in dairy cattle.
Dairy cattle with high milk yields are selectively bred, and their offspring are evaluated for milk production. Artificial insemination using sperm from high-yielding bulls accelerates genetic improvement. This process focuses on heritability of milk production traits and can be aided by genetic screening.
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