Agriculture Reference
In-Depth Information
In the mid-1800s an Austrian
monk named Gregor Mendel was
the fi rst person to begin moving
breeding from an art to a science.
Mendel experimented with peas to
demonstrate that observable traits
could be passed from parents to off-
spring with predictable results. In
his experiments, Mendel used green
peas and yellow peas. But what he
discovered about the genetic process
with those peas applies equally to all
living organisms.
The essence of Mendel's work
demonstrated that inheritance is
controlled by a hereditary unit now
called a gene, that genes come in
pairs (one gene from the mother and
one from the father), and that each
gene maintains its function from
generation to generation. (Mutations
are the rare exception to that last
part, and we'll discuss them in a min-
ute.) Mendel also hypothesized that
each gene could come in different
forms, called alleles. In peas there is
an allele for yellow pods and an allele
for green pods.
Some alleles are dominant and
some are recessive. When a dominant allele is present in a gene pair, the trait
represented by that dominant allele is observable. For peas the green pod
is dominant. For a recessive trait, such as the yellow pod, to show up, both
halves of the gene pair have to have that allele. In reality, most traits in most
animals are the result of not one gene pair, but many gene pairs working
together, referred to as polygenic traits. Some recessive alleles are extremely
undesirable. Lethals are one type of recessive allele. As the name implies, an
animal that receives two lethal alleles dies, often before birth. Fortunately,
lethal alleles by their nature are rare.
Mendel's Genetics Experiment
If you breed a green pea (with two GG
genes) to a yellow pea (with two YY genes),
each offspring will show the dominant
green trait but have one Y and one G gene.
Breed one of these offspring to a yellow
pea (middle row, right above) and half will
show the green trait, half the yellow.
