I. Gregor Mendel “father of genetics”

a. Inheritance Theory Prior to Mendel

1. Traits “blended”

• Trait: characteristics to be passed from parent to offspring

• “bloodlines”: thought traits passed through the blood

2. Problem with blending: cannot account for unexpected traits

II. Mendel- the story

a. Personal history

1. Austrian monk

2. Teacher of high school natural science- love of evolution, nature, meteorology

3. “for the fun of it”: crossed peas and mice- saw inheritance patterns

4. pea plants- a formal test

5. let’s add math:- importance of statistics and ratios: basis for his hypotheses- problem the math created: not used in

biology previouslyb. The research

1. pea plants- why?- structure (male and female parts on same plant)- distinctive traits- rapid reproduction- ability to control pollination and fertilzation

Steps of Mendel's

Experiment

1.   Mendel studied the inheritance of one trait (for example plant's height, color of  flowers or color and shape of seeds).

2.    Mendel first cross pollinated tall pea plants (identified as

TT, height of plants in this variety were about six feet

tall) with each other.

Mendel noticed, that only tall plants were produced. He came to a

conclusion, that the tall variety of a pea plant, must contain some

factor for tallness.

3.   Mendel then cross pollinated short pea plants (identified as tt, height of plants in this variety were about one foot tall) with each other.

X

In every generation of this plant only short plants were produced. Once again he concluded that pea plant must contain some factor for height (in that variety - for shortness).

4.   The next step of Mendel's experiment was to crossed tall pea plants (TT) with short pea plants (tt). The resulting plants were labeled Tt and only tall plants were produced.

T

t

T

t

Tt

Tt

Tt

Tt

All plants were tall

LabelingThe standard way of labeling the variation information of a trait in a

particular organism is using two letters. Capital letters represent information which is dominant. Lowercase letters represent the recessive. The letter being used describes a variation (usually the recessive) of the trait.

• TT stands for a plant where both pieces of height information are dominant - tall. The plant is tall.

Tt stands for a plant where one piece of height information is dominant - tall, and the other is recessive - short. The plant is tall.Tt stands for a plant where one piece of height information is recessive - short, and the other is dominant - tall. The plant is tall.tt stands for a plant where both pieces of height information are recessive - short. The plant is short.

Here we crossed two peas which contained both tall and short information.

T

T

t

t

Tt

Tt

TT

tt

A cross in which only one trait is studied is called monohybrid cross .

5.  Mendel named every generation: Starting generation – P (parent) generation.

The following offspring generation was called

F1 - first generation (daughter generation),

F2 - second filial generation, and so on.

P F1 F2

2. results from experiments- tall x short ----- > all tall- “dominant” ---- > tall- “recessive” ---- > short- hybrid x hybrid ---- > result of crossing F1 generation- led to the idea of gene forms3. the gene- sections of chromosomes coding for a trait- alleles: forms of a gene (ex: tall and short for the gene for height)

4. no blending: Mendel found that blending was not occurring since all traits expressed were either dominant or recessive, but not in between (ex: either tall or short; not medium)

5. example crosses:

AA x AA aa x aa

Aa x Aa

c. Research rejected1. why?- math not previously used in science - public skeptical- information not understood- public distracted by Charles Darwin’s study on evolution

d. Importance of research- evolution: provided genetic support for this theory

- modern genetics studies: we still use much of Mendel’s conclusions in our own theories/ studies in genetics