Punnett Squares and Heredity

Punnett Squares

Mendelian Genetics

Punnett Squares

-A punnett shows the possible outcomes of crossing two parents (having
two parents reproduce)

-Tracks only one trait

-A trait is any inheritable factor

-Can you name some traits?

Multiple Choice

An inheritable factor, such as hair color, is called a

• trait

• DNA

• nucleotide

• punnett square

Punnett Square Misconceptions

-Does not show the actual results of the offspring produced.

-Shows the probability of each possible outcome.

How to Make a Punnett Square

-A grid which contains 4 boxes.

-Parents genotypes are placed on the outside of the box. One parent goes
on one side, the other parent on the top.

- A dominant trait is represented with a capital letter, while recessive traits are

represented with a lower case letter

-Homozygous: AA or aa | Heterozygous: Aa

Multiple Choice

Which of the following is an example of a heterozygous genotype?

• bb

• BB

• Bb

Multiple Choice

Which of the following allele pairs is homozygous recessive?

• RR

• Rr

• rr

Punnett Square Drawings

Draw a punnett square, then add parents to it who are BB (brown eyes) and bb (blue eyes)

In pea plants, round seeds (R) are dominant to wrinkled (r). If a homozygous dominant plant is crossed with a homozygous wrinkled
plant, draw the punnett square.

Probability Percentages

Ratio

Probability (%)

0/4

1/4

2/4

3/4

4/4

Multiple Choice

If green (G) is dominant, and yellow (g) is recessive, what percentage of the plants in the shown punnett square would be green?

• 50%

• 100%

• 75%

• 25%

Practice #1: Brown eyes are dominant to blue eyes. If a homozygous blue eyes parent is crossed
with a heterozygous brown eye parent, what is the probability of them having a blue eyed child?

Practice #2: In deer, albinism is a recessive characteristic (a) to non-albinism (A). If a deer with a genotype of
Aa is crossed with another that has Aa, what is the probability that they produce an albino (aa) deer? Show
your work with a punnett square.

Multiple Choice

T - tall and t = short
In the punnett square below, what belongs in the missing square

• tt

• Tt

• Bb

• TT

Multiple Choice

What allele combination should go in the missing box?

• AA

• Aa

• aa

• none of these

Multiple Choice

In a flowering plant species, red flower color (R) is dominant over white flower color (r). What is the genotype of any red-flowering plant resulting from this species?

• rr

• R

• RR

• RR or Rr

Open Ended

In 1-2 sentences, summarize what you learned in class today.