Genetics and Genetic Engineering

The Study of Genetics

Genetics is the study of inheritance and variation. It seeks to understand the units of genetic action, heredity, mutation, and recombination. Since Darwin's work on the evolution of pigeons, finches, and earthworms, natural historians had been looking for casual mechanisms to explain evolution. The theory of natural selection proposed by both Darwin and independently by Alfred Russell Wallace posited that populations that can adapt to their environment are more likely to pass on their traits to future generations or progeny.

By 1900, natural historians had a prime candidate for the casual mechanisms of evolution when Hugo de Vries, Erich von Tschermak, and Carl Correns rediscovered the basic laws of inheritance. Gregor Mendel, an Austrian monk studying in the 19th century, developed a theory of inheritance while studying the reproduction of peas from 1857–63. According to Mendel, the variation of an organism's characteristics is the outcome of combinations and expressions of genes. For each characteristic of an organism, each individual inherits genes called alleles from each parent. Each characteristic is an expression of an alleles' molecular synthesis. If the alleles differ, some alleles will be dominant with others being recessive. The presence of a dominant allele will express that particular trait, but the recessive allele will still be in the hereditary material of the organism. For a recessive allele to be expressed all the units of heredity must be the same.

Biologists distinguish between phenotype and genotype. The phenotype of an organism is the expression of the organism's traits like eye color or leaf size. The phenotype of an organism can also be affected by its environment, such as when some plants are stunted by exposure to excess light. The genotype is all the hereditary material carried by an organism including the recessive traits not expressed in the organism. The genotype is the coded information found in almost all living cells that are passed along through heredity. The genotype codes for the expression of phenotype, and the phenotype can subsequently altered by its environment.

Soon after the rediscovery of Mendel's work, William Bateson coined the term genetics in 1905. Thomas Hunt Morgan incorporated much of Mendel's work into his own chromosomal theory of inheritance where chromosomes carry hereditary materials. Morgan's work suggested a sex-linked model of inheritance based on the white eye mutation in fruit flies (spp. Drosophila), which has become the model insect for geneticists.

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