The Theory of Evolution
In 1831, Charles Darwin took a voyage to the Galapagos islands. While there he noticed animals on the islands were similar to each other, but also adapted to specific characteristics of the environment. Darwin specifically noticed finch beaks were unique to the type of food available on the island. This made him ponder on the origin of species. After several years, Darwin concluded the finches he observed all came from a common ancestor. In 1859, Darwin published a book called "On the Origin of Species". In his book, he introduced the theory of evolution. The theory of evolution (also referred to as the theory of evolution by natural selection) states that all species on Earth are related and change or evolve over time. The evolution of organisms occurs within a population as a result of natural selection and variation in the genetic sequence of a species.
Although these giraffes are the same species, they are not genetically identical. There are some differences in their genetic material making them unique from each other. These small variations produce different characteristics in giraffes. Darwin's theory of evolution discussed the idea of natural selection that says organisms best suited for the environment will survive and pass their genetic information onto offspring. The giraffes that are better suited for the environment will survive, reproduce and pass their genetic information. Overtime, these successful genes become the predominant characteristics in the population. If the acacia trees the giraffes primarily feed on were to continue to get taller, the tallest giraffes would survive and reproduce. There would still be a variation in giraffe height, but the taller giraffes would be more successful passing their genes onto the next generation. This would cause the population of giraffes to gradually be taller. Evolution is best described as an editing process because it selects individuals with traits best suited for the current environment.
There are three types of evolution:
- Divergent evolution: In divergent evolution a species gradually becomes different from its ancestors over time. This leads to speciation (new species).
- Convergent evolution: In convergent evolution, two distantly related organisms evolve similar structures and traits to adapt to the environment even though the organisms are independent of each other.
- Parallel evolution: In parallel evolution, two unrelated species in the same environment evolve together forming similar characteristics.
What is genetic variability?
Genetic variability describes the potential for a characteristic to vary in a population. Sources of genetic variability are dependent on factors affecting changes in DNA.
- Mutations cause changes in the DNA sequence of an organism.
- Gene flow describes the movement of genes into and out of a population (ex: a bee carries pollen from one population of plants to another population of plants).
- Sexual reproduction occurs when genetic information from two organisms combines creating new combinations that are passed to the offspring.
Genetic variability describes the tendency at which traits in that population may vary. Increases in a population's mutation rate, gene flow, and sexual reproduction will lead to increased genetic variability.
Increased genetic variability allows a population to better adapt to environmental changes. A population with low genetic variability will have a lower chance of adapting to environmental changes.
The trees in this forest have variations within each species. Some may grow to be taller or have resistance to certain diseases. The genetic variability looks at how tree height or resistance varies with the population.
Genetic variation describes the naturally occurring genetic differences among individuals. A population can be examined for many different types of variation. Some variations such as size, color, shape are easy to see. Other variations such as enzyme activity, or changes in DNA that do not result in changes we can physically observe can be harder to determine.
Sources of genetic variability such as mutations, gene flow, and sexual reproduction cause genetic variation.
- As alterations in DNA occur, genes and traits in the organism evolve, increasing variation.
- As new genes are moved into a population, genetic variation increases. If a certain population of a species leaves the area, genetic variation will decrease.
- Sexual reproduction also increases genetic diversity. The reproductive cells of each parent contain genetic information. When these cells combine during fertilization, the genetic information is combined creating new combinations and increasing genetic variation.
Why is genetic variation important?
Genetic variation increases the evolutionary success and survival of a species. It enables organisms to survive better than other organisms in the species when changes occur. The greater the genetic diversity, the greater the resilience of the population.
These salmon have evolved to have different spawning migration timing. Over time, conditions change to favor different spawning times. When conditions favor one variation of salmon, the population of the other variations decrease since spawning is decreased and genetic information from that variation of salmon is not passed onto the next generation. The salmon able to successfully spawn during this new environment causes an increase in the population of those variations of salmon. The genetic variation in spawning migration time has allowed the population of salmon to remain stable.
A mutation is a change in the genetic sequence of an organism and occurs in the DNA of a cell. DNA is made of bases. These bases code for amino acids which form proteins. Proteins play a crucial role in organisms such as enzymes, antibodies, hormones. When DNA is mutated, formation of the protein can be affected.
Mutations can be caused from various factors including:
- Errors while DNA is being replicated or copied before cell division.
- Exposure to chemicals that can damage DNA
- Exposure to radiation such as gamma rays, X-rays and Uv light can also interact with compounds in the cell leading to damaged DNA.
Each of these sources can lead to mutations such as bases of DNA being substituted, changed, added, or deleted.
Variations in a population are caused by mutations. The small variations contributing to the variation in human eye color are a result of mutations in DNA. These mutations are able to be passed onto the next generation because the DNA the mutation occurs in is found in the reproductive cells forming the offspring. Some changes in DNA do not result in variations being passed on to the next generation. In these mutations, the DNA in the reproductive cells is not affected.
Many mutations that occur in organisms are random. Random mutations are changes in the nucleotide sequence of DNA that occur without pattern and introduce new variation into a population.
There are three causes of random mutations in DNA:
- Base substitutions, also called point mutations, occur when a single base in the DNA is changed. These can cause silent mutations where a change in the amino acid the DNA codes for is not changed. A base substitution can also lead to a missense mutation where the base substituted causes a different amino acid to be made. A base substitution can also lead to a nonsense mutation where the base substituted results in the protein chain being truncated.
- Deletions occur when one or more bases is deleted.
- Insertions occur when one or more bases are inserted.
Charles Darwin introduced the theory of evolution that states all species on Earth are related and change or evolve over time. Darwin said evolution of organisms occurs within a population as a result of natural selection and variation in the genetic sequence of a species. Evolution can be best described as an editing process because it selects individuals with traits best suited for the current environment. There are three types of evolution: divergent evolution, convergent evolution, and parallel evolution.
Genetic variability describes the potential for a characteristic to vary in a population. Sources of genetic variability are dependent on factors affecting changes in DNA and include mutations in DNA, gene flow, and sexual reproduction. Genetic variation describes the naturally occurring genetic differences among individuals. These variations may include size, color, shape, enzyme activity, or other changes in DNA. Genetic variation increases the evolutionary success and survival of a species by enabling organisms to survive better than other organisms in the species when changes occur. A mutation is a change in the genetic sequence of an organism and occurs in the DNA of a cell. Many mutations that occur in organisms are random mutations, which are changes in the nucleotide sequence of DNA that occur without pattern.
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What is an example of genetic variability?
Genetic variability describes the potential for a characteristic to vary in a population. An examples includes the trees in this forest which have variations within each species. The genetic variability looks at how tree height or resistance varies with the population.
What is the meaning of genetic variation?
Genetic variation describes the naturally occurring genetic differences among individuals. This may include variations in an animal's size, color, shape ,enzyme activity, or other changes in DNA.
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