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Population Genetics and Evolution - Coggle Diagram
Population Genetics and Evolution
Concepts
Evolution is the gradual conversion of one species into one or, in some cases, several new species.
This occurs mostly by
Natural Selection
Mutations
cause new alleles or new genes to arise that affect the fitness if the individual, making it more or less suitable for its environment.
If the mutation is deleterious, the individual may grow or reproduce slowly or even die early without reproducing.
If a mutation is
harmful
or non-beneficial to the species, it will die off and not pass said allele around very far. If the mutation is
beneficial
individuals harnessing it will grow and reproduce better than those without it, making it more common.
Evolution is an incredibly slow process. It could take a thousand generations/ millions of years to see a notable difference in a species.
During explorations of new lands, people noted the similarities of some plants and animals to those native to their own land.
Charles Darwin- Discovered natural selection mid 1800s, explanation in
Origin of Species
(1859.) Concept of 'survival of the fittest' Gave many findings a new explanation
About this time things like genes, cell theory, chromosomes, etc were discovered as well.
Population Genetics
Pop. genetics
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.
Gene Pool
total number of alleles in all the sex cells of all individuals of a population.
Say 'A' has 4 alleles, A1, A2, A3, and A4. They are most likely not present in equal numbers. G.H. Hardy and G. Weinberg discovered that if only sexual reproduction was involved the ratio between the 4 would stay the same.
Factors that cause the Gene pool to change
- Mutation, accidents, artificial selection, and natural selection.
Mutation- All genomes are subject to mutagenic factors and mutations occur continually. Because of mutations, existing alleles decrease and new ones appear.
Accidents- events in which an organism cannot adapt. They can be small or large Ex: a meteorite hits earth. In this case either all or some of the alleles will be killed off.
Artificial selection- process in which humans purposefully change the allele frequency of a gene pool. Ex: selective breeding of crops
Natural selection- usually described as 'survival of the fittest.' Most significant factor in causing gene pool changes.
Situations in which natural selection does not operate- Cannot operate if individuals are all genetically identical, no competition, all seeds germinate and grow.
Rates of Evolution
Although evolution seems like it occurs over just a few generations, it does not.
Some plants have gone tens of millions of years without diverging into a new species
There is a very rapid speciation occurring in a group of asters in Hawaii
Shortly after Kauai formed 5.2 million years ago, an aster seed arrived, thrived, and reproduced, spreading rapidly in the unpopulated island. Its descendants have diversified into 3 distinct genera with many species. A new group arises about every 500,000 years.
Speciation- natural selection has caused a new species to evolve.
So much change has occurred on a population for many generations that the frequencies and alleles of the population change
Phyletic Speciation
- one species gradually becomes so changed that it must be considered a new species
Usually takes millions of years. The critical feature is that new beneficial alleles arise and are selected for, they become spread throughout the entire population. This is also known as gene flow which occurs in many ways such as pollen transfer, seed dispersal, and vegetative propagation
Pollen Transfer- can be spread via wind or animal mediation (birds, bees)
Seed dispersal- seeds can be carried by wind, floods, animals and stream flow. Migrating animals can carry seeds long distances.
vegetative propagation- a form of asexual reproduction of a plant. Only one plant is involved and the offspring is the result of one parent. The new plant is genetically identical to the parent.
Divergent Speciation
- results from reproductive isolation of two parts of a population.
reproductively isolated
- interbreeding between the two groups is prevented by some barrier.
A-biological reproductive barrier
- any physical, nonliving feature that prevents two populations from exchanging genes
Allopatric/geographic speciation
- the original species is divided into two or more populations that cannot interbreed; speciation results.
Biological Reproductive Barriers
- any biological phenomenon that prevents successful gene flow.
Sympatric Speciation
- when 2 groups become reproductively isolated even though they grow together
hybrid sterility
- One of the earliest postzygotic barriers to arise.
hybrid inviability
- zygote or embryo dies early in development
adaptive radiation
- special case of divergent evolution in which a species rapidly diverges into many new species over an extremely short time, just a few million years.
Founder effect- loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. It was first fully outlined by Ernst Mayr in 1942
Divergent Speciation
- some populations of a species evolve into a new, second species while other populations either continue relatively unchanged as the parental, original species or evolve into a new third species.
Convergent evolution
- if 2 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 the Origin of Life
Chemosynthesis
- the chemosynthetic hypothesis attempts to model the origin of life using only known chemical and physical processes, rejecting all traces of diving intervention.
First proposed by Russian scientist, A. Oparin in 1924, then by J. B. S. Haldane in England.
They postulated the earth's surface used to be different than the way it is now and was able to create more complex chemicals.
4 Conditions would have had to been present to support the chemosynthetic origin of life
1: the right inorganic chemicals
2: appropriate energy sources
3: a great deal of time
4: an absence of oxygen in its destructive molecular form (O2)
Graduate student S. Miller in 1953 conducted an experiment to show the chemosynthetic origin of life is possible.
He constructed a container that had boiling water in the bottom and a reducing atmosphere in the top; electrodes discharged sparks into the gases, simulating lightning. As the water boiled, steam rose and mixed with the atmosphere and was acted on by the electrical sparks and then condensed and fell back into the water to be cycled again.
The chemosynthetic theory postulates a long series of slow, gradual transitions from completely inorganic compounds to living bacteria
Conditions on Earth Before the Origin of Life
The first atmosphere made up of hydrogen was lost in space due to it being a light gas. The
second atmosphere
replaced it and was produced by a release of gases from the rock matrix composing earth and from heavy bombardment of meteorites
the second atmosphere was also a
reducing atmosphere
due to its lack of molecular oxygen and the presence of powerful reducing agents
The chemistry must have been complex due to its exposure of of powerful energy sources such as UV and gamma radiation from the sun.
Monomers present in the early ocean had to polymerize if life were to arise but this required high concentrations of monomers.
Aggregates
It is not believed that these aggregates were alive or even had the early stages of life because at that point no means of storing genetic information existed. At some point, presumably an aggregate formed that did not have inheritable information molecule able to direct the synthesis of products useful to the aggregate.
The presence of heredity changed everything. Any mutation that caused the production of a more efficient, more advantageous enzyme or structural protein provided a strong selective advantage and could be passed on to progeny aggregates. Currently, attention is focusing on RNA is the first heritable information molecule. As the aggregate increased in size its information molecule would replicate
These first aggregates would have formed basically at random, controlled only by relative solubility. If some of the proteins had some enzymatic activity by chance, the aggregate would have had some simple metabolism perhaps a conversion of some molecule, absorb from the sea, and to another molecule; the aggregates would have been heterotrophs completely
Early Metabolism
The aggregates would have been complete heterotrophs, absorbing all material from the ocean and modifying only a few molecules. As they continue to consume certain nutrients however scarcity occurred. Being able to synthesize valuable scarce molecule From an abundant free one which gave it an advantage because it would have a more rapid metabolism and would have grown and reproduced more rapidly as well.
The diagram prior shows the ability to synthesize the scarce molecule from an abundant one still available in the ocean. This would be the metabolic pathway two steps long that involves two enzymes
Oxygen
The evolution of chlorophyll a and photosynthesis had to profound consequences when it allowed the world to rust into it created conditions that selected for the evolution of aerobic respiration. The atmosphere present today was derived from the early second atm by this edition of oxygen from photosynthesis.
