11.1 THE WORK OF GREGOR MENDEL (THE PEA MONK)

1. Every living thing- plant or animal, microbe, or human being – has a set of characteristics inherited from its parents or parent.

Heredity holds the key to what makes each species unique. The scientific study of heredity is genetics.

2. Gregor Mendel, an Austrian monk, had a very great life studying math and science, teaching high school, and piddling in the monastery gardens.

This man was fascinated with ordinary garden peas. He could never ever be bored because these things are the source of a great deal of knowledge 

3. Pea flowers produce pollen, which contains the male plants’ reproductive cells or sperm (stamen). The flowers also have female parts, which produce egg Cells (carpel). # 4 & 5 make up the male parts = pollen #2 & 3 make up the female part.

Fertilization produces a new cell, which develops into a tiny 4. During sexual reproduction, the male and female cells join, a process called fertilization. Fertilization produces a new cell, which develops into a tiny embryo encased within a seed.

The seeds that are produced inherit 5. Pea flowers are normally self-pollinating, which means that sperm cells in pollen fertilize the egg cells in the same flower. The seeds that are produced inherit all of their characteristics from the single plant that bore them. They have a single parent!

6. Mendel discovered that his pea plants were true-breeding, meaning that if they were allowed to self-pollinate, they would produce offspring identical to themselves!! One stock of seeds would produce only tall plants, another short ones. One line produced green seeds, another yellow ones.

7. Mendel wanted to produce seeds by joining sperm and eggs from two different plants. To do this he had to prevent self-pollination!!! This is what he did! He cut away the pollen-bearing male parts then dusted pollen from another plant onto the flower.

7. This process is called cross-pollination. It produced seeds that had two different plants as parents! This made it possible for Mendel to cross-breed plants with different characteristics, and then study the fascinating results!!

8. Mendel studied seven different pea plant traits. A trait is a specific characteristic that varies from one individual to another. Each of the 7 traits Mendel studied had two contrasting characters, such as green/yellow seeds color, tall/short plants, etc.

9. Mendel crossed plants with contrasting characters and studied their offspring. He called the original set of parents the P (parental) generation. He called the offspring the F1 “first filial” generation. The offspring of crosses between parents of diff traits are called hybrids.

Hybrids from a cross between a tall plant and a short plant

10. Mendel was a busy man. He was also surprised 10. Mendel was a busy man! He was also surprised! All of the offspring in the F1 generation had the character of ONLY one of the parents! The character of the other parent seemed to have disappeared!!...Was this magic? Or was there another explanation?

Hybrids from a cross between a tall plant and a short plant

11. Mendel drew two conclusions: 1. Biological inheritance is determined by factors that are passed from one generation to the next. (Today, we call the chemical factors that determine traits genes. Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms.)

11. (These contrasting forms produced the different characters of each trait. The diff forms of a gene are called alleles).

X = Purple X = Axial X = Yellow X X X X

2. The Principle of dominance states that some alleles are dominant & others are recessive. An organism with the dominant form of an allele will always exhibit that form of the trait.

2. An organism with the recessive allele for a particular form of a trait will exhibit that form ONLY when the dominant allele for that trait is NOT present!!

12. Mendel wanted to know if the recessive alleles had disappeared, or were they still present in the F1 plants?? He allowed all seven kinds of F1 hybrid plants to produce an F2 (2nd filial) generation by self-pollination.

13. The results of the F1 cross were REMARKABLE!! When Mendel compared the F2 plants, he discovered that the traits controlled by the recessive alleles had reappeared!! Roughly ¼ of the F2 plants showed the trait controlled by the recessive allele!!!

Recessive allele traits reappeared in about ¼ of the F2 plants P Generation F1 Generation F2 Generation Recessive allele traits reappeared in about ¼ of the F2 plants

14. WHY did the recessive alleles seem to disappear in one generation and reappear in the next??? The answer is segregation!!! The reappearance of the recessive trait (short plant in this case) indicated that it had somehow become separated from the allele for tallness.

So how did this separation or segregation occur So how did this separation or segregation occur? Mendel suggested that the alleles for tallness and shortness in the F1 plants segregated from each other during the formation of the sex cells, or gametes.

15. If F1 plants inherit an allele for tallness from one parent and an allele for shortness from another parent, all the F1 plants are tall because the allele for tallness is dominant.

When each F1 plant flowers and produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes ---those with the allele for tallness and those with the allele for shortness.

Figure 11-5 from pg. 266 Draw and Label Gamete formation: alleles