BIO 370 Lecture Notes - Lecture 9: Blending Inheritance, Heredity, Transversion
Transmission Genetics and the Sources of Genetic Variation
The advent of agriculture 10,000 years ago certainly carried with it the notion that traits
present in the parental stock of one generation somehow affect the traits in offspring
generations.
The question
at the time of
Darwin was:
How?
Early formal ideas on inheritance
Work of Joseph Kölreuter (18th century) supported the theory of blending inheritance.
Credited with first experimental study of inheritance (1761-1766).
Bred tobacco plants and found that offspring were usually intermediate between parents.
What is Blending Inheritance?
This is the idea that the factors that dictate heredity are blended together from one generation
to the next.
Both parents make an equal contribution to the traits of the offspring.
Consequences for Evolution
• By the mid-19th century it was believed that these blended traits could change over
generations, typically through acquired inheritance.
• Laak’s idea of auied iheitae.
Blending Inheritance
reduces diversity
Initial population is half big, half
short, half red, half white.
Let’s look at the fate of this
particular combination.
REMEMBER: THIS IS THE BOUNDS OF THE SECOND GENERATION! NEXT GEN CAN BE NEITHER
TALLER NOR SHORTER, NOR REDDER NOR WHITER.
Blending Inheritance
cannot explain
re-emergence
of traits.
The problem was that there was no good alternative.
• Darwin’s theory of natural selection not his entire theory was scientifically criticized
early on because blending inheritance would eliminate beneficial characteristics in
one or a few generations, much faster than would occur by natural selection.
I.e., for lack of an alternative, blending inheritance held sway
Problem was, blending did explain a lot of traits inheritance and there was’t a ette
alternative in explaining the rest.
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The major questions of this section are:
How does an understanding of DNA, amino acids, and proteins help solve the dilemmas
encountered by blending theory, and open up a much broader view of inheritance and
transmission genetics?
What is transmission genetics, and how does our understanding of this topic affect the way that
we study the process of evolution?
Transmission genetics – transmitting genetic material from one generation to the next.
Mendel cleverly focused on traits which preliminary experiments seemed to show were
inherited independently of one another*
• 8 years, 5,000 plants, on 4.9 acres of pea plants that had been first planted in 1830 by
his mentor.
• Started with pure-bred strains and then crossed them.
• He also back-crossed the offspring with the pure-bred parental lineages.
• In short, a large, sophisticated experiment with controls with lots of data subjected to
rigorous statistical analysis.
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There had to be two factors determining color in each individual.
One factor for purple and one for white. One (purple) was dominant to the other (white.) The
presence of the dominant factor determined color.
Factors were inherited randomly from each parent, meaning that one had to separate or
segregate from the other.
Mendel crossed parent plants that were true-breeding (homozygous) for two discrete
phenotypes of a particular trait. In the example here, pea plants with purple flowers (PP) were
crossed with pea plants with white flowers (pp). In the F1 generation, all hybrids were purple
(Pp). In the F2 generation, the majority of the plants were purple, but some were white.
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find more resources at oneclass.com
Document Summary
Transmission genetics and the sources of genetic variation. The advent of agriculture 10,000 years ago certainly carried with it the notion that traits present in the parental stock of one generation somehow affect the traits in offspring generations. Work of joseph k lreuter (18th century) supported the theory of blending inheritance. Credited with first experimental study of inheritance (1761-1766). Bred tobacco plants and found that offspring were usually intermediate between parents. This is the idea that the factors that dictate heredity are blended together from one generation to the next. Both parents make an equal contribution to the traits of the offspring. Consequences for evolution: by the mid-19th century it was believed that these blended traits could change over generations, typically through acquired inheritance. Initial population is half big, half short, half red, half white. Let"s look at the fate of this particular combination. Remember: this is the bounds of the second generation!
