Gregor Mendel.notebook
March 22, 2011
Gregor Mendel and Pea Plants
In 1822, Gregor Mendel was born in Austria. When he was 21 years old, he entered a monastery, where the monks taught science and performed experiments. Mendel was sent to school to learn how to teach, but he had trouble taking tests, and he failed his final exam.
So, Gregor Mendel went back to the monastery to do research, and he decided to study pea plants.
Mendel looked at many different characteristics (a feature that has different forms in a population) of pea plants, including:
1) seed shape: round or wrinkled
2) seed color: yellow or green
3) plant height: tall or short
4) flower color: purple or white
5) flower placement: axial (at the stem) or terminal (at the tips)
6) pod shape: smooth or bumpy
7) pod color: green or yellow
We call the different forms of the characteristics ­ traits.
Gregor Mendel.notebook
March 22, 2011
Mendel made sure his pea plants were true breeding, which means if the plant pollinates itself, the offspring always have the same traits as the parents.
Pollen, which contains sperm, comes off the anthers of a flower, and lands on the stigma. The pollen travels down to the ovary, and fertilizes the ovule (egg). This becomes the seed for the next generation of plants.. Mendel noticed that sometimes a trait in one generation (the parent generation) of pea plants wasn’t present in the first set of offspring (the F1 generation). But, the trait showed back up in the second set of offspring (the F2 generation).
Example: Flower color
Gregor Mendel.notebook
March 22, 2011
Mendel always got the same results, with the same traits as the parents. He realized the traits didn’t blend, (a popular theory of inheritance at the time), because he didn't get offspring that had a mixing of the parents' traits.
Mendel called the trait that appeared in the First Generation the dominant trait. The trait that seemed to go away, or recede, he called the recessive trait.
In Gregor Mendel’s next set of experiments, he self pollinated the First generation of offspring, and got some surprising results:
Flower color:
Parent Generation:
First Generation:
Second Generation:
Ratio:
Purple flowers
X
White flowers
Gregor Mendel.notebook
March 22, 2011
He found the same results for the other traits, too:
705:224
3.15:1
651:207
3.14:1
6022:2001
3.01:1
5474:1850
2.96:1
882:299
2.95:1
428:152
2.82:1
787:277
2.84:1
Mendel realized the only way he could get these results was if each plant had two sets of "instructions" for each characteristic. Each parent donates one set of "instructions" to the offspring.