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Life: the Science of Biology by Purves, Sadava, Orians, Heller
Evolution in genetic terms means changes in proportions of alleles present in a population for a particular trait across generations.
Genes have different forms called alleles. If the two copies of a gene are identical alleles, this is a homozygous condition. If the two allele copies are different, this is a heterozygous condition.
The alleles a person inherits are his or her genotype. Observable functional or physical traits, such as attached earlobes, are the phenotype. The gene pool is the total of all the alleles in a population.
Population is a localized group of individuals that belong to the same biological species and who are capable of interbreeding and producing viable offspring. A population's gene pool is defined by its allele frequencies.
A species is a group of potentially interbreeding organisms that produce fertile offspring and share similar characteristics. Speciation is the splitting of one species into two or more species or the transformation of one species into a new species over time; speciation is the final result of changes in gene pool allele and genotypic frequencies.
1. What are the mechanisms of evolution?
Evolution occurs through the process of descent with modification. All life is made up of cells. Cells arise from pre-existing cells. As life perpetuates itself over time, differences appear and these differences accumulate and cause different species to come into existence.
It is not individuals that evolve, it is populations that do. In order for a population to evolve, there must be heritable genetic variation among its members. The mechanisms that change the genetic structure of a population and cause evolution are: Mutation, migration (gene flow), genetic drift, nonrandom mating, and natural selection.
1) Mutation: Mutation is any change in the DNA of an organism. Any mutations in the reproductive cells (eggs and sperms) of an organism are inherited. Mutations can alter allele frequencies within a population by changing one allele into a different allele. The DNA affects the structure and functions of an organism. Thus any change in DNA can cause a change in an organism.
2) Migration (gene flow): Gene flow (or gene migration) is the movement of alleles among populations by migration. Allele frequencies change when individuals leave a ...
Answers four questions on mechanisms of evolution, natural selection, mutation etc.