Transcript 3.2 Punnett Squares

Big Punnett-ing

Catalyst:
Six
fingers (S) is dominant over five
fingers (s). What is the phenotype of a
person who is heterozygous?
How did Mr. LY decide to use the letters
“S” and “s” to represent dominant and
recessive, above?
Write in complete sentences!
Don’t talk during the Catalyst!
Objectives
By the end of today, SWBAT…

Create and analyze Punnett Squares
Agenda
Catalyst Review
 Making Babies Lab (GASP!)
 Punnett Squares
 Guided Practice
 Independent Practice
 Closing

Remember…

GENotype = Combination of
alleles inherited from the
parents (the GENes)
PHenotype = PHysical
expression of the trait

Before we get started, remember…
CAPTIALIZED letters are DOMINANT
 lowercase letters are recessive
Examples:
B = brown hair (DOMINANT)
b = blonde hair (recessive)
Y = yellow (DOMINANT)
y = green (recessive)
P = purple (DOMINANT)
p = white (recessive)

Before we get started…
D = dimples
d = no dimples
Homozygous
dominant
Homozygous
recessive
Heterozygous
recessive
Genotype: DD
Genotype: dd
Genotype: Dd
Phenotype:
have dimples
Phenotype: no
dimples
Phenotype:
have dimples
Before we get started…
B = brown eyes
b = blue eyes
Homozygous
dominant
Homozygous
recessive
Heterozygous
recessive
Genotype: BB
Genotype: bb
Genotype: Bb
Phenotype:
brown eyes
Phenotype:
blue eyes
Phenotype:
brown eyes
Today, you are going to have 20 kids.
What?
 Yes. In 15 minutes, you will have 20
kids.
 You will need to find someone in the
class to mate with.
 We will demonstrate how this works.

Making Babies Lab!
Each partner has one lunch bag. Each lunch
bag represents the genes that person gives to
their child.
 Inside the bag are the two alleles for ONE
gene.
 To make a baby…

 WITHOUT
looking into the bag, reach in and grab a
letter (your partner will do the same).
 Record the genotype in the table below.
 YOU HAVE JUST MADE A BABY.
Key Point #1

Punnett Squares are diagrams that are
used to predict the genotypes of
offspring.
Probability…not EXACT
It is important to note that Punnett
Squares only give probabilities for
genotypes
 They don’t give you the EXACT
outcomes

Big Pun-nett

Let’s make our own. First things first, draw yourself
box and split it into 4 squares.
Punnett like its Hot
Read the problem and find the parents’
genotypes.
 Remember to use the first letter of the
dominant trait.

BB
A homozygous dominant brown eyed male mates
with a heterozygous female.
Bb
Punnett Squares are COOL


Parents go on the top and on the left (keep each
parents’ alleles together)
It doesn’t matter which parents goes on the top or
the left
B
B
B
b
Punnett Square Dance


Now, bring them together.
The four boxes represent the possible kids.
B
B
B
BB
BB
b
Bb
Bb
Just Punnett!


Now, we analyze.
Use quarters to figure out percentages.
•How many homozygous
dominant do we have? 50%
•How many heterozygous do
we have? 50%
•How many homozygous
recessive do we have? 0%
B
B
B
BB
BB
b
Bb
Bb
Punnett baby one more time

Lastly, figure out percentages by phenotypes.
•What percentage will
have brown eyes? 100%
B
B
B
BB
BB
b
Bb
Bb
•What percentage will
have blue eyes? 0%
Let’s do one more on the board

A heterozygous dimpled male mates with a
heterozygous dimpled female.
Whiteboard Guided Practice: Seed Shape

R
R
R
RR
RR
r
Rr
Rr


R = round
r = wrinkled
Solve the following
Punnett Square.
A homozygous
dominant round
seeded plant is
crossed with a
heterozygous wrinkled
plant.
Find the genotype and
phenotype
probabilities.
Guided Practice: Earlobes

F
f
f
Ff
ff
f
Ff
ff


F = free
f = attached
Solve the following
Punnett Square
A male with attached
earlobes mates with a
heterozygous female.
Find the genotype and
phenotype
percentages.
Oh, how we love Spongebob!
Mr. LY will now pass out the “Punnett
Squares – Spongebob Style” worksheet
 We’ll do some of them together… then you
get to try the rest on your own!

Exit Question
D = dimples, d = no dimples
Create a Punnett
Square for two parents
who are heterozygous.
List the percent of
children that will have
each genotype AND
each phenotype.