What did the discovery of the underlying mechanism of heredity by Mendel allow?
Darwin’s theory of evolution by natural selection to become the grand unifying
theory of biology. It put the descent into the idea of “modification by descent”.
What does the underlying mechanism involve?
The underlying mechanism involves the equal segregation of particulate determinants
(now known as alleles) when reproductive cells (gametes) are formed, and their reassociation at fertilization, allowing reassortment. Each individual receives one allele from each parent and fertilization is random between gametes. Phenotype is simply the fortuitous combination of different sets of determinants, which behave independently from one another*. There is no blending, and no modification of determinants**.
What does the multifactorial hypothesis suggest?
That Mendelian genetics is completely consistent with the idea of evolution driven by natural selection, because continuous variation is the result of the action of many discrete determinants (loci) all individually obeying
Mendel’s laws. The active alleles of several QTLs contribute more or less additively to the
metric character. A histogram of metric traits in the progeny of a multiply heterozygous
individual shows a bell-shaped curve typical of continuous variation. This idea suggests that genetics is not really deterministic for most characteristics, but probabilistic, because of the number of loci involved.
What does genetics tell you?
Genetics is not just limited to hereditary mechanisms, but tells you about all biological
mechanisms.Genetic dissection of a biological property (forward genetics) begins with a
collection of mutants with varying phenotypes, and allows particular genes to be associated with particular processes. Forward genetics is an extremely powerful approach that has been successfully pursued in a range of model organisms, from bacteria to mouse.
