BIO - Unit 5: Monohybrid & Punnett Square Review

Reviewing Monohybrids &

Punnett Squares

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.

Match

Match the following terms with their definitions.

• Inherit

• Genes

• Trait

to get traits from parents' genes

parts of DNA that code for trait

characteristic you get from your parent

• to get traits from parents' genes

• parts of DNA that code for trait

• characteristic you get from your parent

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

Match

Match the following term to its example.

• Dominant Allele

• Recessive Allele

• Homozygous Genotype

• Heterozygous Genotype

H

g

KK

Dd

• H

• g

• KK

• Dd

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.

Reorder

Put the steps for completing a Punnett Square in order.

• Determine the genotypes of the parents

• Write the alleles for each parent on the top and side of the Punnett Square

• Fill in the Punnett Square

1

2

3

• 1
• 2
• 3

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

Match

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

Match the parent to their genotype.

• heterozygous tall plant

• homozygous short plant

• .

Tt

tt

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

Draw

Label the parent genotypes on the outside of the Punnett Square.

Remember! One parent was Tt and the other parent was 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

Draw

Fill in the Punnett Square.

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

Multiple Choice

A heterozygous tall plant (Tt) was crossed with a homozygous short plant (tt). Based on the completed Punnett square, what percentage of the offspring will be tall?

Remember that each box represents 25%.

• 0%

• 25%

• 50%

• 75%

Multiple Choice

A heterozygous tall plant (Tt) was crossed with a homozygous short plant (tt). Based on the completed Punnett square, what percentage of the offspring will be homozygous?

Remember that each box represents 25%.

• 0%

• 25%

• 50%

• 100%

Multiple Choice

Cross a homozygous dominant tall plant (TT) with a heterozygous tall plant (Tt). How many of the offspring will be tall?

• 0 out of 4

• 1 out of 4

• 2 out of 4

• 3 out of 4

• 4 out of 4

Multiple Choice

Cross a parent with dimples (Dd) with a parent without dimples (dd). What percentage of the offspring will not have dimples?

• 0%

• 25%

• 50%

• 75%

• 100%