Transcript B - JhaveriChemBioWiki

Wednesday – September 23, 2009
Objectives:

SWBAT create and analyze Punnett Squares.
Catalyst:
 What is the difference between a gene
and an allele?
 How do we represent dominant alleles?
Recessive alleles?
Agenda
Catalyst Review
 Making Babies Lab (GASP!)
 Punnett Squares
 Guided Practice
 Independent Practice
 Closing

Catalyst


A gene codes for a trait- eye color, ear lobes,
dimples, etc.
An allele is a different version of a gene.
 Ex:
Brown vs. Blue eyes
 Ex: Attached vs. Free hanging earlobes
 Ex: Dimples vs. No dimples
Review Yesterday’s Vocab
Traits
 Allele
 Homozygous
 Heterozygous
 Dominant
 Recessive

Check
your
awesome
notes!
Remember…
GENOTYPE = combination of
alleles inherited from the
parents (the genes)
PHENOTYPE = physical
expression of the trait

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.
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
 It doesn’t give you the EXACT
outcomes

You
will see when we start creating
our Punnett Squares
Key Point #2

You can never know for sure
what offspring will look like,
you can only predict based on
probability.
Key Point #3

We refer to the parent generation as P1 and the
offspring of that generation as F1.
P1
F1
Before we get started…
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
Genotype: DD
Genotype: dd
Phenotype:
have dimples
Phenotype: no
dimples
Heterozygous
Genotype: Dd
Phenotype:
have dimples
Before we get started…
B = brown eyes
b = blue eyes
Homozygous
dominant
Homozygous
recessive
Genotype: BB
Genotype: bb
Phenotype:
brown eyes
Phenotype:
blue eyes
Heterozygous
Genotype: Bb
Phenotype:
brown eyes
Big Pun-nett

Let’s make our own. First things first, draw yourself
box and split it into 4 squares.
Punnett like its Hot


Now, read the problem and find the parents’
genotypes.
*Remember, use the first letter of the dominant trait.
BB
A homozygous dominant brown eyed male mates with a
blue eyed female.
bb
Punnett Squares are COOL


Parents go on the top and on the left (keep them
together)
It doesn’t matter which parents goes on the top or
the left
B
B
b
b b
b
Punnett Square Dance


Now, bring em together.
The four boxes represent the possible kids.
B
b
b
B
Bb
Bb
Bb
Bb
Just Punnett!


Now, we analyze.
Use quarters to figure out percentages.
B
•How many homozygous dominant
do we have? 0%
•How many heterozygous do we
have? 100%
•How many homozygous recessive
do we have? 0%
b
b
B
Bb
Bb
Bb
Bb
Punnett baby one more time

Lastly, figure out percentages by phenotypes.
•What percentage will have
brown eyes? 100%
•What percentage will have
blue eyes? 0%
B
b
b
B
Bb
Bb
Bb
Bb
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 free
hanging earlobe
female.
Find the genotype and
phenotype
percentages.
Oh, how we love Spongebob!
Your teacher will now pass out the GP & IP
“Punnett Squares – Spongebob Style”
worksheets
 We’ll do some of them together…then you
get to try the rest on your own!

Wrap Up
Punnett Squares are diagrams that are
used to predict the genotypes of
offspring.
 You can never know for sure what
offspring will look like, you can only
predict based on probability.
 We refer to the parent generation as P1
and the offspring of that generation as
F1.

Exit Question
Create a Punnett
Square. Do a cross of
two heterozyous
parents for brown
eyes. List the
genotypes &
phenotypes
probabilities of both the
P1 and F1
generations.