1. Chapter 4 Section : Patterns of Heredity
Objectives:
1. I can use Punnett squares to understand patterns of heredity
2. I can use ratios and probability to describe patterns of heredity
3. I can Analyze experimental data to find probabilities.

2. Punnett Squares Mendel noticed that traits are inherited in patterns.
A punnett square is a tool that illustrates how the parents’ alleles might combine in offspring.
Each parent has two alleles for a particular gene
An offspring will receive one allele from each parent.
A Punnett square shows how the parents alleles may be passed to potential offspring.

3. Punnett Squares
D D d
The top of the Punnett square shows one parents alleles
The side shows the other parents alleles
Each box in the Punnett square shows a way the alleles would combine in the offspring
D = Regular Height d = dwarf height

4. Ratios and Percentages
A ratio compares the relationship between two quantities.
Punnett Squares and their ratios express probability
Probability is the chance of a specific outcome in relation to the total number of outcomes.
The ratios from a Punnett square, tell you the probability that any one offspring will get certain genes and express a certain trait.

5. Ratios and Probability
If one parent has 2 dominant traits, and the other has two recessive traits, there is a 100% chance that the offspring will have the dominant phenotype.
If both parents have 1 dominant and 1 recessive trait, there is a 75% chance that the offspring has the dominate phenotype.
Punnett squares and probability do not guarantee the outcomes of a genetic cross
They indicate the probability of different outcomes.
Actual experimental results may not match predicted outcomes.

6. Alleles
An organism is considered homozygous dominant or homozygous recessive if it receives the same two alleles
Ex. – BB (homozygous dominant)
Ex. – bb (homozygous recessive)
An organism is considered heterozygous for a trait if it has one of each allele.
Ex. - Bb