What is genetic load? This explanation is found at the linked website:
"Genetic load is a measure of the number of harmful mutations an average member of a population is carrying. Although harmful recessive mutations will be selected against, they will not generally be eliminated from a population because once such mutations are present at a very low frequency, it will be rare for any two individuals carrying them to mate. As a result, most individuals in stable populations carry a number of recessive lethal mutations, termed their "genetic load".
There is a dubious claim made. Is a recessive mutation, causing a deleterious phenotype, selected against? Of course if the mutation is not expressed because of a dominant allele there is no basis for selection. But if there are two recessive alleles and a deleterious trait is expressed, will the reproductive fitness of the effected organism be compromised? Probably not.
Organisms display many thousands of phenotypic effects. Most are functional and benefit the organism. However, some compromise fitness without being lethal. Organisms are composites of mostly functional parts mixed with sub-optimal functions resulting from mutations. The capacity to reproduce despite impaired functions is characteristic of life.
This post is a table setter for another one to come which will focus on assumptions embedded in evolution.
Labels: Natural Selection