Define the term "mutation." Describe how frequently mutations occur in individual genes and in the total gene pool of a population. Are mutations generally beneficial or harmful? What advantage do diploid organisms have over haploid organisms in terms of being protected from harmful mutations?
Mutations, or slight changes in the chemical structure of a gene, occur at random and are caused by a variety of influences. Mutations occur at very low rates for individual genes, but, because of the large total number of genes in organisms, mutations are constantly occurring within a species. Rarely is a mutation beneficial. The majority of new mutations are deleterious because of their randomness; in fact, mutations can create lethal alleles that have phenotypic expressions which kill the organism. Because natural selection acts on phenotypes and only indirectly on genotypes, only dominant deleterious mutations can be selected against. Recessive mutations are not easily selected against because usually an organism will have one normal dominant allele that masks the deleterious mutated recessive allele. Such mutations remain in populations for long periods of time. The advantage of diploidy is that deleterious recessive alleles can be masked, whereas, in haploidy deleterious mutations are always expressed.
