Chapter 9 Introduction to Genetics
Developed by Nancy Manikas (6-21-97)

Heredity - biological inheritance

Genetics - branch of biology that studies heredity

I. The Work of Gregor Mendel

A. Early Ideas About Heredity

Theory of Blending Inheritance:

B. Gregor Mendel

- Austrian Monk in the 1850's

- teacher, put in charge of gardens

- studied pea plants which are normally _____________________. Mendel cut off the male parts of one plant and the female parts of the other and _____________________ his pea plants. He crossed plants with different characteristics and observed what happened.

- he was working with ________________ pea plants.

- he decided to study just a few isolated ___________ that could be easily observed:

- size of plant
- shape of pod
- color of seed

C. Genes and Dominance

- Mendel produced ___________ by crossing tall and short plants, for example.

- Mendel found that characteristics did not __________ as expected. Offspring has characteristics of one of the parents.

- __________ - factors that control traits.

1. Mendel found that individual factors (genes) controlled each trait.

- ______________ - different forms of a gene (eg. "tall" and "short" are alleles of the gene for height).

2. Mendel also came up with the principle of dominance.

- some factors (alleles) are _______________, while others are __________________. If you mix a dominant and a recessive, only the dominant trait shows up.

D. Segregation

Mendel then crossed the hybrids to see what would happen. He called:

P generation - ____________ parental plants

F₁ generation - ___________ generation = first generation of plants produced by cross-pollination.

F₂ generation - result of crossing ____________ (produced in F₁)

gametes - reproductive cells

The F₁ Cross:

 

This can be better represented using a Punnet Square.
Click here for more information.

Results:

1/4 of the plants are TT (tall) purebreds
1/2 of the plants are Tt (tall) hybrids
1/4 of the plants are tt (short) purebreds

Phenotype - how the plants look - the physical characteristics (3/4 look tall in the above example; 1/4 look short)

Genotype - genetic makeup of the organism (1/4 TT; 1/2 Tt; 1/4 tt in the above example)

Homozygous:

Heterozygous:

E. Independent Assortment (2 factor crosses)

Mendel wanted to know if alleles segregate independently. He chose:

P -->

F-->

1. If the two traits are linked (i.e. on the same chromosome), then:

gametes would be _______ and _______

 

	RY	ry
RY
ry

2. If the two traits are not linked (on different chromosomes), then the gametes would be:

________, ________, _________, __________

This is called independent assortment.

 

	RY	Ry	rY	ry
RY
Ry
rY
ry

II. Applying Mendel's Principles

A. Genetics and Probability

- Probability is ___________________________________________

 

- Probability = ------------------------------------------------------------------

- example: What is the probability of getting "heads" when flipping a coin?

- example: What is the probability of pulling a king from a deck of cards?

- example: What is the probability of pulling a "club" from a deck of cards?

- you only get the expected ratios with a _________ number of trials.

- previous events do not affect ___________ ____________.

B. Using the Punnet Square

Work the two sample problems on page 191.

Do the section review questions on page 192.

Link to Chapter 9 Part II: Meiosis