Mutations present permanent and heritable changes in the genome. We distinguish gene and chromosome mutations. Mutations in the level of genes are called point mutations because only one to several nucleotides are changed. These processes are known as deletion, insertion, and substitution. Deletion presents a loss of nucleotides which changes DNA sequence. When new nucleotides are embedded in the DNA chain, it is known as insertion. Substitution implies the process where new nucleotides are inserted while the ones that were present in that specific spot in a DNA molecule are deleted.
Mutations can also appear in chromosomes altering their number and structure. There are four types of mutations - deletion, duplication, inversion, and translocation. In deletion, a whole or one part of a chromosome is lost. Duplication presents an extra copy of a whole or one part of a chromosome. In an inversion, parts of a chromosome change order, while in translocation a part of one chromosome detaches and then connects to another.
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<span>Plato first proposed that the planets followed perfect circular orbits around the Earth. Later, Heraclides (330 B.C.) developed the first Solar System model, placing the planets in order from the Earth it was is now called the geocentric solar system model.
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