Mendel and Heredity

Ch 11.1-3 - Genetics

Genetics

• Study of Heredity• Passing of traits from parents to offspring

• Trait: a specific characteristic

Gregor Mendel

• Father of genetics• Parents were farmers• He became ordained as a

priest• Studied science & math at

Univ of Vienna

Mendel’s Experiments

• Chose Pea plants as exp. Subjects–Easy to cross–Grow quickly–Produce high number offspring–Showed variety of contrasting

traits• Purple vs white flowers• Tall vs short stems• Round vs wrinkled seeds

Mendel’s experiments cont.

1. Chose true breeding lines of each plant/trait he studied.

a. True breeding always produced offspring of the same type

2. Crossed a true breeding plant with a plant of the opposite trait. (purple x white)

a. Called this the Parental (P) generation

3. Recorded data on the offspring of this cross. (hybrid)

3) First Filial generation (F1)

4. Self pollinated the F1 offspring5. Recorded data on the offspring

of the 2nd generation.5) Second Filial generation (F2)

Analysis: F1 Generation

• Always displayed one trait (he later called this the dominant trait)

• Must have within it the trait from the original parents – the white trait

Analysis: F2 Generation

• Displayed the hidden trait, ¼ of the F2 gen. had it (he later called this hidden trait the recessive trait)

• Each individual has 2 ”factors” that determine what external appearance the offspring will have– These factors are now called genes or

alleles

Mendel established 3 principles or laws from his research

The Principle of Dominance and Recessiveness

One trait is masked or covered up by another

trait

Principle of Segregation

The 2 factors (alleles) for a trait separate during gamete formation

Principle of Independent Assortment

Factors of a trait separate independently of one another during gamete formation.

Example:

• Whether a flower is purple has nothing to do with the length of the plants stems – each trait is independently inherited.

Modern Genetics

• Mendel’s factors are now called Alleles. (different versions of a gene)

–For every trait a person has, 2 alleles determine how that trait is expressed

• We use letters to denote alleles, since every gene has 2 alleles, all genes can be represented by a pair of letters

PP = purple,Pp = purple pp = white

Terms to know:

• Homozygous:

When the alleles are the same.

(true breeding)

Ex. AA, bb, EE, dd

Terms to know:

• Heterozygous:

When the alleles are different.(dominant allele is

expressed)

Ex. Pp, Aa, Bb

Terms to know:

• Genotype:

Letters used to denote alleles

(BB, Pp, aa)

Terms to know:

• Phenotype:

What an organism looks like.

(brown, purple, curly hair….)

Terms to know:

• Monohybrid cross:

a cross involving one pair of contrasting traits.

Ex. Pp x Pp

Terms to know:

• Punnett Square:

Used to determine the Probability of having a certain type of offspring given the alleles of the parents.

How to solve a Punnett Square:

1. Determine the genotypes (letters) of the parents.

1. (AA x aa ) or (Rr x Rr)2. Set up the punnett square w/one

parent on each side.3. Fill out the punnett square middle.4. Analyze the number of offspring of

each type.