Chapter 5 Notes 

I.                 Mendel and His Peas

Heredity-passing of traits from parent to offspring

A.Who Was Gregor Mendel?

Monk in Austria/worked in monastery gardens

B. Unraveling the Mystery

Patterns of inheritance not always clear

Studied pea plants


1. Self-Pollinating Peas

Pea plants-grow quickly, different traits to study, could self pollinate

True-breeding=all offspring like parent

Cross-pollination=1 plant fertilizes another

2. Characteristics

Feature with different  forms in a population

Ex-hair color, eye color, vision

Trait-different forms of a characteristic

Ex-brown hair, blue eyes, near-sightedness

3. Mix and Match

Cross-pollinated plants with different traits

Ex-purple flowers with white flowers

C. Mendel’s 1st Experiments

1st generation-parent gen

1st gen of offspring-1st generation or f1

Traits that always showed-dominant

Traits that disappeared and reappeared-recessive

D.                        Mendel’s 2nd Experiments

Recessive trait reappears in 2nd gen

1. Ratios in Mendel’s Experiments

Ratio of dominant to recessive- 3 to 1

2. Gregor Mendel-Gone but Not Forgotten

Mendel’s work not recognized until 30 yrs after death

Mendel’s Laws of Heredity

1.  Mendels Law of Segregation.   

Get 1 trait from both parents

2. Law of Independent Assortment

Get a mixture of traits from both parents

II  Traits and Inheritance

A.                      A Great Idea

Gene-instructions for traits

Alleles-different forms of genes

1.           Phenotype



Phenotype-appearance/looks like


Albinism-no color in hair, eyes, skin


2.           Genotype

Genotype-gene pair Pp, BB, bb

Homozygous-2 dominant or recessive genes  PP or bb

Heterogygous-2 different genes  Pp or Bb

3.           Punnett Squares-shows ratios

4.           More Evidence for Inheritance


B.                      What Are the Chances?

Coin toss, 50% chance for heads

1.           Probability-mathematical chance something will happen

Probability-written as fraction or per cent

2.           Calculating Probability

Each time you toss coin, multiply by 1/2

3.           Genotype Probability

C.                      More about Traits

1.           Incomplete Dominance



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