1. Chapter C3
Section 2 Traits and Inheritance
A Great Idea
Mendel knew that there must be two sets of instructions for each characteristic.
The instructions for an inherited trait are called genes.
The different forms (often dominant and recessive) of a gene are alleles.
An organism’s appearance is known as its phenotype. Genes affect the phenotype.

2. Chapter C3 A Great Idea, continued
Section 2 Traits and Inheritance
A Great Idea, continued
The combination of inherited alleles together form an organism’s genotype.
Punnett Squares are used to organize all the possible genotype combinations of offspring from particular parents.

3. Chapter C3
Section 2 Traits and Inheritance

4. Chapter C3 What Are the Chances?
Section 2 Traits and Inheritance
What Are the Chances?
Probability is the mathematical chance that something will happen.
Probability is most often written as a fraction or percentage.

5. Calculating Probability
Chapter C3
Section 2 Traits and Inheritance
Calculating Probability

6. What Are the Chances?, continued
Chapter C3
Section 2 Traits and Inheritance
What Are the Chances?, continued
Genotype Probability To have white flowers, a pea plant must receive a p allele from each parent. Each offspring of a Pp Pp cross has a 50% chance of receiving either allele from either parent. So, the probability of inheriting two p alleles is 1/2  1/2, which equals 1/4, or 25%.

7. Chapter C3 More About Traits
Section 2 Traits and Inheritance
More About Traits
Incomplete Dominance Researchers have found that sometimes one trait is not completely dominant over another.
One Gene, Many Traits Sometimes one gene influences more than one trait.
Many Genes, One Trait Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together.

8. More About Traits, continued
Chapter C3
Section 2 Traits and Inheritance
More About Traits, continued
Genes aren’t the only influences on traits. A combination of things determine an individual’s characteristics.
Your environment also influences how you grow.
Lifestyle choices can also affect a person’s traits.