Selection in Humans

Both natural and artificial selection occur in human beings. If a trait is lethal and kills before reproductive maturity, then that gene mutation is gradually depleted from the population. Mutations with milder effects persist longer and are more common than very severe mutations, and recessive mutations persist for much longer than dominant ones. With a recessive trait, such as albinism, the parents are usually both carriers of a single copy of the gene and may not know that they carry it. If a child receives a copy of this gene from both of the carrier parents, the albino child may die young, may find it difficult to find a partner, or may end up marrying much later in life. This is usually considered a form of natural selection.

Considerable abuse of genetic knowledge in the first half of the twentieth century led to the eugenics movement. Advocates of eugenics claimed some people were more fit and others less fit (or unfit), and argued that the least fit should be persuaded or forced not to reproduce. Eugenicists typically defined as unfit those who were "feeble-minded, criminal, socially deviant, or otherwise undesirable." Coerced sterilization, a form of artificial selection, was practiced on some of these individuals. see also Cloning Genes; Eugenics; Hardy-Weinburg Equilibrium; Muller, Hermann; Mutagenesis; Mutation.

Elof Carlson

Bibliography

Huxley, Julian. "Adaptation and Selection." In Evolution: The Modern Synthesis. New York: Harper and Brothers, 1942.

Pianka, Eric. Evolutionary Biology, 6th ed. San Francisco: Addison-Wesley-Longman, 2000.

recessive requiring the presence of two alleles to control the phenotype dominant controlling the phenotype when one allele is present eugenics movement to "improve" the gene pool by selective breeding il

Sequencing DNA

A gene is a segment of DNA that carries the information needed by the cell to construct a protein. Which protein that is, when it is made, and how damage to it can give rise to genetic disease all depend on the gene's sequence. In other words, they depend on how the building blocks of DNA, the nucleotides A, C, G, and T (adenine, cytosine, guanine, and thymine) are ordered along the DNA strand. For example, part of a gene may contain the base sequence TGGCAC, while part of another gene may contain the base sequence TCACGG. Knowing a gene's base sequence can lead to nucleotides the building blocks of RNA or DNA

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