Download Probability of Inheritance Lesson 2

PROBABILITY OF
INHERITANCE
LESSON 2
Mrs. Anna Ward
Seventh Grade Science
Ridge Road MS
DO NOW!!!!
• Copy down this diagram in your notes!!!!
Agenda
• Review from yesterday.
• What is a Punnett Square?
• Why do we use them?
• What can they tell me?
• How to do a Punnett Square
• Six Steps to Success
• Discovery Ed video
• Think, Pair, & Share Practice
Punnett Square…What are they and why do we
use them?
•A Punnett Square is a chart used to show
the possible ways genes from two parents
can combine in order to predict possible
genotypes of offspring
•Punnett Squares also help us determine
the probability and ratios of these
offspring.
Punnett Squares—
STEP ONE
Identify the
Genotypes of
Each Parent!
In this case:
TT and tt
PUNNETT SQUARES
STEP TWO
DRAW
A BOX
WITH A
CROSS.
Punnett Squares—
STEP THREE
Add the Genotype
information from
One parent across
the top.
Add the Genotype
information from
the other parent
down the side.
TT x tt
Punnett Squares—
STEP FOUR
Add the
Alleles from
One Parent
to the
Punnett
Square.
TT x tt
Punnett Squares—
STEP FIVE
Add the
Alleles from
the other
Parent to the
Punnett
Square.
TT x tt
Punnett Squares—
STEP SIX
Calculate the Results
The final result of
crossing a Pea Plant
(TT) with a Pea
Plant (tt) is that all
the offspring will
have the
GENOTYPE “Tt”.
CFU: If all the
genotypes are “Tt”
what is the
phenotype? (Are
they tall or short?)
However, if those
two plants are
crossed…
What Happens???
Remember step
one…IDENTIFY
THE PARENT
GENOTYPES!
Tt x Tt
STEP 2
Draw
the Box
with a
cross.
STEP 3
Add in the
Genotypes of
the parents
across the
top and
down the
side.
Tt x Tt
STEP 4
Add the
alleles from
one parent
into the
Punnett
Square
Tt x Tt
STEP 5
Add the
alleles from
the other
parent into
the Punnett
Square
Tt x Tt
NOTE: When writing genotypes,
the DOMINANT allele ALWAYS
comes first!!!!!
Step 6—Calculate
the Final Results..
When crossing two plants with a Tt
genotype we get…
• One plant with the
genotype TT
• Two plants with the
genotype Tt
• One plant with the
genotype tt
Checking for
Understanding…
What are the phenotypes for the
Genotypes of this Punnett Square?
• One plant with the
genotype TT
• Two plants with the
genotype Tt
• One plant with the
genotype tt
In other words, we get three tall plants
for every one short plant.
Discovery Ed Video to help explain….
• http://player.discoveryeducation.com/index.cfm?guidAssetId=AB33
E612-2755-4901-8A44-857151E3BB24
Punnett Squares
• The type of Punnett Squares we are doing are MONOHYBRID
CROSSES.
• Monohybrid Crosses are used to evaluate the potential genotypes
of offspring when looking at traits that are determined by a single
allele.
• You will need to know the steps for completing a Monohybrid Cross
(or Punnett Square).
• Glue in the Punnett Square Cheat Sheets into your science
notebook.
Now it is time for you to practice…
1.
What would the result of crossing a Heterozygous Tall pea plant
(Tt) with a homozygous Tall pea plant?
2. What would be the result of crossing a homozygous Short pea
plant (tt) with a homozygous Short pea plant (tt)?
3. What would be the result of crossing a heterozygous Tall (Tt) pea
plant with a homozygous Short pea plant?
4. What would be the result of crossing a heterozygous tall pea
plant with a heterozygous tall pea plant?
Exit Ticket…
1.
Which of the following is a heterozygous genotype?
a.
Aa
b.
BB
c.
cc
d.
DD
2. What is another name for the type of Punnett Squares we are
completing?
3. What would happen if I cross a HOMOZYGOUS DOMINANT
Brown Haired Woman (BB) with a HOMOZYGOUS RECESSIVE
Blond Haired Man?