Sriharsha Kota

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Genetic Variation

        Genetic variation has many important parts to it, a big portion being mutation. A mutation is a change in the nucleotide sequence of DNA dealing with its genes and alleles. A point mutation is a change in a single base in a nucleotide sequence. That being said, the origin of how a mutation forms is mutagenesis. There are three types of point mutations: substitution, frame shift(insertion and deletion), and an editing error. Substitution is the replacement of one nucleotide and its partner with another pair of nucleotides. A frame shift mutation occurs whenever the number of nucleotides inserted or deleted is not a multiple of three. While dealing with mutations, several characteristics must also be included. These are randomness, non-directionality, change in phenotypic traits, and gametic change. These all contribute to how a mutation may be classified going from physical descriptions to the very gametes themselves. An example of a mutation could occur when sickle cell anemia occurs because of a mutation in protein structure.

        The following part deals with chromosomal mechanisms. There are four different results that occur when there is chromosomal breakage. A deletion occurs when a chromosomal fragment lacking a centromere is lost. Sometimes a deleted fragment may become attached as an extra segment to a sister chromatid, producing a duplication. A chromosomal fragment may also reattch to the original chromosome but in the reverse orientation, producing an inversion. A fourth possible result of chromosomal breakage is for the fragment to join a nonhomologous chromosome, a rearrangement called a translocation. Crossing over greatly contributes to genetic variation in the fact that it is the reciprocal exchange of genetic material. When there is an abnormal chromosome number, an aneuploidy can occur. The chromosomal alteration for organisms that havemore than two complete chromosome sets is polyploidy. Some other mechanisms are transposable elements, virus induced charges, and genetic engineering. A transposable element is a segment of genetic material that is able to change its position in the genome. Genetic engineering is a technique used to duplicate or manipulate genetic material. The changes induce by a virus is also classified in this category of chromosomal mechanisms.

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        The way in offspring are even produced is by sexual reproduction. When two parents contribute genetic material, they go through meiosis and crossing over occurs, which reshuffles traits promoting diversity. Recombination occurs when individual chromosomes that carry genes derived from two different parents. The principle in which each homologous pair of chromosomes is positioned independently of the other pairs into daughter cells is called independent assortment. Random fertilization adds to the genetic variation arising from meiosis. When offspring are created with gene pool connection, it is called cross breeding.

        Darwin’s theory of natural selection is divided into five observations. ...

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