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Population genetics and Evolution (evolution and origin of life…
Population genetics and Evolution
Population Genetics
Factors that causes gene pool to change
Mutation
due to mutation there is decrease in the frequency of the existing alleles and there is increase in new alleles
the significance of mutation also depends on the population size.
Accidents
accidents are the events to which an organism cannot adapt.
if the population of a area has the same gene frequencies and sudden accidents happen in such area and the animals or plants are killed then that gene frequency is lost from earth.
Artificial Selection
it is the process in which humans purposefully change the allele frequency of a gene pool.
for example: selective breeding of crop plants and domestic plants.
natural selection
the most significant factor causing gene pool changes also called survival of the fittest.
natural selection is the most important factor in evolution.
for natural selection to occur, there are two conditions necessary:
the population must produce more offspring that can possibly grow and survive to maturity in that habitat
the progeny must differ from each other in their types of alleles.
Multiple selection pressures
the loss of an individual does not depend on a single factor, but it depends on many factors.
there are multiple internal and external factors that does carry out the selection process.
Speciation: natural selection has caused a new species to evolve, a process called speciation.
Phyletic Speciation
pollen transfer
: pollen grains are transferred long distance by the wind. If a pollen grain sperm cells can fertilize a egg cell which is different then an embryo might be formed with new allele.
seed dispersal
: long distance seed dispersal can help in the process of speciation
vegetative propagation
: if a species produces small, mobile pieces that reproduce vegetatively, they too contribute to gene flow. thousands of combinations can be done through vegetative propagation.
Divergent Speciation
Abiological reproductive barriers: any nonliving, physical feature that prevents two populations from exchanging genes.
biological reproductive barrier: any biological phenomenon that prevents successful gene flow is a biological reproductive barrier.
Convergent Evolution: if two distinct, unrelated species occupy the same or similar 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 strongly and are said to have undergone convergent evolution.
evolution and origin of life
conditions on earth before the origin of life
chemicals present in the atmosphere: earth was condensed with gases and dust 4.6 billion years ago. there was lack of molecular oxygen in the atmosphere
Energy sources: there was intense UV and gamma radiation
from the sun
part of ammonia must have decomposed to hydrogen and nitrogen adding complexity to the atmosphere
time available for the origin of life: the time available for the chemosynthetic origin of life basically had no limits because of lack of free molecular oxygen.
chemicals produced chemosynthetically
the miller experiment suggested that essential molecules for life like amino acids, sugars, lipids, nitrogen bases were formed non living environments.
formation of polymers
formation of polymer occurred because polymers were necessary to be formed from monomers for life to arise
Aggregation and organization
the next possible step in evolution of life would have been the aggregation of chemical components in masses that had some organization and metabolism.
early metabolism
oxygen
the evolution of chlorophyll a and photosynthesis had two profound consequences: 1. it allowed the world to rust.
it created conditions that selected for the evolution of aerobic respiration.
the presence of life
Rates of Evolution
evolution is a very slow process.
very few mutations produce a new phenotype.
Rate of evolution is a measurement of the rate of genotype change of species and organisms over a period of time.
