What are we learning? Why are we learning this?
content, procedures, skills
Tier II: High frequency words used across content areas. Key to understanding directions, understanding relationships, and for making inferences.
Tier III: Low frequency, domain specific terms
Building on what we already know
What vocabulary & concepts were learned in earlier grades?
Make connections to prior lessons from this year.
This is where we start building from.
This next section is from Basic Principles of Genetics: An Introduction to Mendelian Genetics, Dennis O’Neil, Behavioral Sciences Department, Palomar College, San Marcos, California, http://anthro.palomar.edu/mendel/mendel_1.htm
For thousands of years farmers and herders have been selectively breeding their plants and animals to produce more useful hybrids.
It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown.
Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half.
By the 1890’s, the invention of better microscopes allowed biologists to discover the basic facts of cell division and sexual reproduction.
The focus of genetics research then shifted to understanding what really happens in the transmission of hereditary traits from parents to children. A number of hypotheses were suggested to explain heredity, but Gregor Mendel, a little known Central European monk, was the only one who got it more or less right.
His ideas had been published in 1866 but largely went unrecognized until 1900, which was long after his death. His early adult life was spent in relative obscurity doing basic genetics research and teaching high school Greek, mathematics, physics, in Brno (today, this town is in the Czech Republic.)
Today Brno is in the Czech Republic – but that nation didn’t exist at that time. Back then it was part of “The Margraviate of Moravia” – hey, I never heard of that either! Not a full-size nation, it was a marcher state existing from 1182 to 1918. – RK
In his later years, he became the abbot of his monastery and put aside his scientific work.
While Mendel’s research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals.
Through the selective cross-breeding of common pea plants (Pisum sativum) over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics.
How did Mendel cross-breed peas? Let’s start with the basics:
Plants with flowers have gendered sex-organs (male and female)
He found a way to take advantage of this, to breed plants as desired.
Mendel decided to study seven traits that are easily recognized, and easy to track as they only occur in one of two forms:
1. flower color is purple or white
2. flower position is axil or terminal
3. stem length is long or short
4. seed shape is round or wrinkled
5. seed color is yellow or green
6. pod shape is inflated or constricted
7. pod color is yellow or green
This observation that these traits do not show up in offspring plants with intermediate forms was critically important
His results would soon disprove the then-leading idea:
Some scientists in the 19th century, including Charles Darwin, were considering a model called “pangenesis”.The idea was that hereditary molecules in our bodies are affected by what we do during our lifetime. These modified particles were thought to migrate via blood to the reproductive cells (sperm or eggs.) Subsequently these changed traits would be inherited by the next generation.
The pangenesis hypothesis allowed for the possibility that a change to you, could be inherited by your children.
The germ-plasm hypothesis means that changes to you, could not be inherited by your children.
It turned out that the germ-plasm concept is right.
Today we don’t use the word “germ” – we call these particles “chromosomes”
Pea plants can either self-pollinate (sex with one parent)
or cross-pollinate with another plant. (sex with two parents)
This illustrations shows how Mendel was able to selectively cross-pollinate purebred plants with particular traits
He then could observe the outcome over many generations.
From Ask-A-Biologist: Mendel’s Garden