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Population Genetics and Evolution (Population Genetics (It deals with the…
Population Genetics and Evolution
Population Genetics
It deals with the abundance of different alleles within a population and the manner in which the abundance of a particular allele increases, decreases, or remains the same with time.
The genetic recombination that occurs during several reproduction is important only if the two sexual partners have different genotypes.
Crossing-Over also increases genetic diversity in population.
The total number of alleles in all the sex cells of all individuals of a population constitutes the gene pool of the population.
Evolution is the gradual conversion of one species into one or in some cases, several new species.
Evolution occurs for the most part by natural selection.
-Mutation causes new alleles or new genes to arise that affect the fitness of the individual.
As evolution by natural selection continues, the types and abundances of alleles present in the species change, and consequently, the phenotype also changes.
Evolution is an extremely slow process that may require thousands of generations and millions of years to produce obvious changes in species.
Alfred Russel Wallace and Charles Darwin independently discovered the basis-natural selection in the mid 1800's, the critical explanation being given in Darwin's Origin of New Species published in 1859.
Factors that cause the gene pool to change
Accidents
: Accidents are events to which an organism can not adapt, such as the collision of a large meteorite with earth.
Artificial Selection:
It is the process in which humans purposefully change the allele frequently of a gene pool.
Mutation
: Because of mutation, existing alleles decreases frequently, and new alleles increases.
Natural Selection:
- It is the most significant factor causing gene pool changes.
It is usually described as survival of the fittest.
Two conditions myst be met before occurring natural selection.
1) The population myst produce more offsprings that can possibly grow and survive to maturity in that habitat.
2) The progeny must differ from each other in their types of alleles.
Convergent Evolution:
If two distinct, unrelated species occupy the same habitats, natural selection may favor the same phenotypes in each. As a consequence, the two may evolve to the point that they resemble each other strangely and are said to have undergone convergent evolution.
Evolution and the Origin of Life
Chemosynthesis: The most seriously considered hypothesis about the origin of life on earth.
Factors that are not part of natural selection
It does not include purpose, intention, planning, or voluntary decision making.
Speciation
Natural selection has caused a new species to evolve, a process called speciation.
-Speciation can occur in two fundamental ways.
1)
Phyletic speciation in which one species gradually becomes so changed that it must be considered a new species.
2)
Divergent speciation in which some population of a species evolve into a new second species while other population either continue relatively unchanged as the original, parental species or evolve into a new third species.
If alleles that arise in one part of the range do not reach individuals in another part, the two regions are reproductively isolated.
Conditions on earth before the origin of life.
Chemical present in the atmosphere
Earth condensed from gases and dust about 4.6 billion years ago.
Second atmosphere produced by the release of gases from the rock matrix composing earth and from heavy bombardment by meteorites (reducing atmosphere)
Energy sources
Formost was intense UV and gamma radiation
Head another source of energy.
Oxygen
The evolution of chlorophyll a and photosynthesis that liberates oxygen had to profound consequences. 1) It allowed the world to rust and it created conditions that selected for the evolution of aerobic respiration. The atmosphere present today was derived from the early second atmosphere. By, this addition of oxygen from the photosynthesis, it is an oxidizing atmosphere.
