Download Chapter 4 Section : Patterns of Heredity

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.

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.

Punnett Squares
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D
D
d
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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

Ratios and Percentages
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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.
Ratios and Probability
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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.
Alleles
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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