Students will learn about Punnett squares. Students will gain practice in completing a monohybrid cross Punnett square and will be exposed to dihybrid crosses, but are not required to do these.
2. LET’S REVIEW!
What is Mendel’s Law of
Segregation?
The 2 alleles for each trait
separate during meiosis
During fertilization, 2 alleles
for that trait unite
3. LET’S REVIEW!
What is Mendel’s Law of
Independent Assortment?
A random distribution of
alleles occurs during gamete
formation
Monohybrid cross results in 4
possible gametes
4. PUNNETT SQUARES
What can Punnett Squares help you
do?
Can help PREDICT ratios of
dominant to recessive traits in the
genotype of offspring
2 types
Monohybrid cross: looking at 1
trait – 2 x 2
Dihybrid cross: looking at 2 traits –
4 x 4
5. PROBABILITY
The inheritance of genes can be compared to the
probability of flipping a coin
The probability of a coin landing on heads is 1 out of 2
or ½
If the same coin is flipped twice, the probability of
landing on heads is ½ each time or ½ x ½ or ¼ both
times
6. BEGINNER’S GUIDE TO PUNNETT
SQUARES
Mr. Andersen’s Beginner’s Guide to Punnett
Squares:
https://www.youtube.com/watch?v=Y1PCwxUD
Tl8
7. CHECKING FOR UNDERSTANDING
Who was Gregor Mendel?
How do Punnett Squares help you predict possible
offspring?
What does the 9:3:3:1 ratio tell you?
8. PUNNETT SQUARE PRACTICE
One flower is
heterozygous red (Rr)
and it is crossed with a
homozygous white (rr)
plant. Create a Punnett
square to determine
the probability of one
of their offspring
having a red color.
9. PUNNETT SQUARE PRACTICE
In a species of plant, the color purple (P)
is dominant to the color white (p). If a
homozygous purple plant is crossed with
a homozygous white plant,
What is the probability of the offspring
being purple?
What about white?
** Create a Punnett square to show your
work**
10. GENETICS PRACTICE
Use the table above to answer the questions.
SpongeBob Squarepants is heterozygous for
his squarepants shape. What is his genotype?
SpongeBob’s wife SpongeSusie is
homozygous for her roundpants shape. What
is her genotype?
Characteristic Dominant Gene Recessive Gene
Body Shape Squarepants (S) Roundpants (s)
11. PUNNETT SQUARE PRACTICE
Characteristic Dominant Gene Recessive Gene
Body Shape Squarepants (S) Roundpants (s)
Spongebob and SpongeSusie want to have children. Draw a
Punnett Square to show the possibilities.
1. List the possible genotypes and phenotypes for the kids.
2. What is the probability of kids with squarepants?
3. What is the probability of kids with roundpants?
12. LET’S RECAP!
In a monohybrid corss, how many traits are you looking
at?
In a dihybrid cross, how many traits are you looking at?
Do you think Punnett squares are 100% accurate? Why
or why not?
