the science of genetics
started, people tried to reproduce organisms with only the most preferred traits, by allowing only those organisms
with the desireable traits to reproduce. This method was not always successful, but through time (trial and error),
this practice of controlled breeding provided scientists with the information to determine which alleles were responsible
for specific traits.
purebred organisms, a breeder would choose pure bred parents, those parents whose ancestors have produced only
the desired characteristic they want (true-breeding). If a breeder chooses two different 'true-breeds' then a hybrid
would be produced.
two different true-breeds will result in all of the offspring having the same characteristic, that is, the dominant trait. Only the DNA instructions for the dominant trait will be carried out.
hybrids, the average results will produce 75% of the offspring with the dominant trait and 25% of the offspring
with the recessive trait, because there are only 4 possible combinations. One traits is recessive and therefore
the allele is recessive. A recessive trait only appears in the offspring if two recessive alleles are inherited.
Other Patterns of Inheritance
dominance occurs because the dominant-recessive
pattern does not alwys prevail. When the alleles are neither dominant, nor recessive, an intermediate trait will
occur (combining the two traits).
Unlike Either Parent. More than one gene location and more than one allele may be responsible for specific traits. As a result, the variation
of traits an offspring has may be accounted for by the complex mixing of the possibile combinations for that particular
Factors can also have a bearing on how DNA
is interpreted and developed. Fetal alcohol syndrome can be a direct result of alcohol consumption during the developing
stages of the offspring. The 'normal' DNA is affected by the alcohol and will not develop normally. Taking drugs
can also affect the DNA during normal development and defects in the organism can occur. (Thalidimide)