BIO - Unit 5: Monohybrid & Punnett Square Review

What is Heredity?

• Heredity is the passing of traits from parents to offspring.

• Inherit: To get traits from parents through their genes.

• Genes: parts of DNA that decide what traits you will have.

• Traits: Features or characteristics you get from your parents.

Genes & Alleles

• Genes carry information for a trait, and alleles are different forms of the same gene

• Example: The gene for flower color has different versions/alleles of purple or white.

What is a Monohybrid Cross?

• A monohybrid cross examines the inheritance of a single trait.



• Example: Crossing a tall plant with a short plant. This example is focused on the height of the plant.

Key Vocabulary

• Dominant Allele: Masks the effect of the recessive allele. Written as an uppercase letter
ex: T

•Heterozygous: Having two different alleles for a particular gene.
ex: Tt

• Recessive Allele: Only seen when both alleles are recessive. Written as a lowercase letter
ex: t

•Homozygous: Having two identify alleles for a particular gene.
ex: TT or tt

How a Punnett Square Works

• Step 2: Write the alleles of each parent on the top and side.

• Step 3: Fill in the squares by combining the alleles.

• Step 1: Figure out the genotypes of each parent.

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and
short (t)

Steps:
1. What are the genotypes (alleles) of
each parent?
______Tt_______ x _______tt_______
(heterozygous tall) (homozygous short)

2. Put the alleles for each parent outside
the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and short (t)

Steps:
1. What are the genotypes (alleles) of each parent?

2. Put the alleles for each parent outside
the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and short (t)

Steps:
1. What are the genotypes (alleles) of
each parent? Tt & tt

2. Put the alleles for each parent outside the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a

homozygous short plant. Tall (T) and
short (t)

Steps:
1. What are the genotypes (alleles) of
each parent?
______Tt_______ x _______tt_______
(heterozygous tall) (homozygous short)

2. Put the alleles for each parent outside
the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and short (t)

Steps:
1. What are the genotypes (alleles) of
each parent? Tt & tt

2. Put the alleles for each parent outside the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and short (t)

Steps:
1. What are the genotypes (alleles) of
each parent? Tt & tt

2. Put the alleles for each parent outside the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt

Example of a Punnett Square

• A heterozygous tall plant with a homozygous short plant. Tall (T) and short (t)

Steps:
1. What are the genotypes (alleles) of
each parent? Tt & tt

2. Put the alleles for each parent outside the Punnett Square.

3. Fill in the Punnett Square.

T

t

t

t

Tt

Tt

tt

tt