BIOL 311 Lecture Notes - Lecture 1: Gregor Mendel, Plant Breeding, Heredity
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1.1 The Birth of Genetics
Throughout recorded history, people around the world have understood that
“like begets like.” Children resemble their parents, the seed from a tree
bearing flavorful fruit will in turn grow into a tree laden with flavorful fruit,
and even members of wolf packs show familial resemblances.
In the 1800s in Europe, horticulturalists, animal breeders, and biologists also
sought to explain the resemblance between parents and offspring.
A commonly held view at that time was the! !blending theory
or the belief that inheritance worked like the mixing of fluids such as paints.
Red and white paints, when mixed, give pink; and so a child of one tall parent
and one short parent could be expected to grow to a middling height.
While blending theory seemed to work at times, it was also clear that there were
exceptions, such as tall children born to parents of average height.
Blending theory also provided no mechanism by which the “heredity fluids” it
imagined, once mixed, could be separated—the red and white paints cannot be
reconstituted from the pink.
Thus, the long-term expectation of blending theory over many generations of
intermating among individuals is that all members of the population will come to
express the same average value of a trait. Clearly, this is not how nature works.
Human populations have people with a range of heights, from short to tall, and
we have not all narrowed in on a single average height despite the many
generations that human populations have dwelled on Earth.
Gregor Mendel—A monk in the garden
While the merits and failings of blending theory were being debated, Gregor
Mendel, an Austrian monk, was working to understand the rules that govern the
transmission of traits from parent to offspring after hybridization among
different varieties of pea plants.
(meaning of hybridization - the process of an animal or plant breeding with an individual of another species or variety.)