Punnet Squares
!  Objective: SWBAT explain what a
punnett square is and use a punnett
square.
!  Warm Up: Why do sex cells (Sperm,
eggs) only have 23 chromosomes and
not 46 like the rest of our cells?
Career of the
Week!
Genetic Engineer
!   a scientist who modifies the genes of organisms to
help diagnose diseases, develop new crops, and
better medications.
!   Education- Bachelors Degree (Science)
Doctoral Degree (Ph.D.)
!   Average Salary- $65,110 per year
!   Duties- working in a team, doing labs everyday,
experimenting on animals before people.
Quick Review
!  Dominant vs Recessive
!  If one parent gives you the allele for blue
eyes, and another parent gives you the
allele for brown eyes, you will most likely
have brown eyes.
!  Why?
Time to be VAIN together!
What about you?
!  Widow’s Peak
!  Earlobes
!  Dimples
!  Taco Tongue?
Notes
Phenotype:
Latin Root:
“Pheno” means
“to show”
An organism’s physical
appearance or visible trait.
*you CAN see this!
Notes
Genotype: An organism s allele
combination.
*you can t see this, it s in the
nucleus
Writing Genotypes
(1). The first letter of the dominant
allele is the letter used.
(2). The capital letter represents a
dominant allele.
(3). The lower case letter represents
a recessive allele.
Example: Brown and Blue Eyes
(1). If brown is the dominant allele, which
letter are we going to use?
(2). Does brown get a capital or lower
case letter?
(3.) Does blue get a capital or lower case
letter?
Writing Genotypes
If a person has two alleles for brown, the
genotype is: BB
If a person has two alleles for blue, the
genotype is: bb
If a person has one allele for brown, one
for blue, the genotype is: Bb
Quick Check (Think-Pair-Share)
!  Why do we have two alleles for each
gene?
Quick Check
!   Which one describes the phenotype
(PHYSICAL trait you can see), brown or BB?
!   Which describes the genotype (GENETIC
makeup that you can t see), brown or BB?
!   If the genotype is Bb, what is the phenotype?
Trait: Dimples
Dimples are dominant over No dimples.
1. What letter will we use to represent the
dimples trait?
2. For the Dimples allele, do we use D or
d?
3. For the No Dimples allele, do we use D
or d?
Trait: Dimples
4. If you get a Dimples allele from your
dad and a No Dimples allele from your
mom, what is your genotype?
5. If you get a Dimples allele from your
dad, and a No Dimples allele from your
mom, what is your phenotype?
Trait: Nose Shape
Pointy nose shapes are dominant over
round nose shapes.
1. If you get a Round nose allele from
your dad and a Round nose allele
from your mom, what is your
genotype?
2. If you get a Round nose allele from
your dad and a Round nose allele
from your mom, what is your
phenotype?
New Vocabulary:
!  Hybrid or Heterozygous: when the 2 alleles
are different
•  Ex. Bb, Rr, Ww
!  Homozygous: when the 2 alleles are the
same
•  Ex. BB, bb, WW, ww, RR, rr
Punnett Squares
!  Punnett Square:
a tool used to see all the
possible combinations
of alleles from the
parents.
Here is how Punnett Squares
work…
•  Mom s alleles (PP: Purple flowers)
•  Dad s alleles (pp: white flowers)
P
p
Pp
P
Pp
p
Pp
Pp
!   All four offspring would be Purple flowers (Pp)
(4/4=100% Pp)
Example:
!  Freckles (F) are dominant over no freckles
(f). The mother is a heterozygous freckled
woman (Ff) and the father is a homozygous
non-freckled man (ff). They have a baby.
What is the likelihood that the baby will
have freckles?
!  Mom: (Ff)
Dad: (ff)
What did you get?
!   Freckles (F) are dominant over no freckles (f). The mother is a heterozygous
freckled woman (Ff) and the father is a homozygous non-freckled man (ff).
They have a baby. What is the likelihood that the baby will have freckles?
!   Mom: (Ff)
Dad: (ff)
Example # 2:
!  Curly hair is dominant to straight hair. If a
HETEROZYGOUS Curly haired man had a
baby with a HYBRID Curly Haired woman,
what is the likelihood that the babies will
have curly hair?
What did you get?
!   Curly hair is dominant to straight hair. If a HETEROZYGOUS Curly haired
man had a baby with a HYBRID Curly Haired woman, what is the likelihood
that the babies will have curly hair?
Video
!  http://www.brainpop.com/science/
cellularlifeandgenetics/heredity/
Homework
!  Complete the two punnett square
questions on the back of your notes.
November 21, 2011
(Page 73)
!  Objective: SWBAT predict the outcome
of a genetic cross using a punnett
square.
!  Catalyst:
Write a heterozygous genotype:
Write a homozygous genotype:
Punnett Square Review
!  What is the difference between
dominant and recessive alleles?
Punnett Square Review
!  Why is a genotype always written with
two alleles?
Punnett Square Review
!  What is a phenotype?
Punnett Square Revew
!  How is the genotype related to the
phenotype?
Punnett Square Review
!   Freckles are dominant over no freckles. The
mother is a heterozygous freckled woman (Ff) and
the father is a homozygous freckled man (FF).
They have a baby. What is the likelihood that the
baby will have freckles?
Homework Review
!  Question #1. Brown eyes (B) are dominant
over blue eyes (b). A blue-eyed woman (bb)
and a brown-eyed man (BB) have a child.
(1). What is the genotype of the woman?
(2). What is the phenotype of the woman?
(3). What is the genotype of the man?
(4). What is the phenotype of the man?
Homework Review
!   (6) How many boxes have BB? __________
Bb? __________
bb? __________
!   (7) Of the four boxes, how many show brown-eyed babies?
!   (8) Of the four boxes, how many show blue-eyed babies?
!   (9) What is the probability of this couple having a browneyed baby? (give a fraction)
!   (10) What is the probability of this couple having a blueeyed baby? (give a fraction)
Homework Review
!  Question #2. Freckles (F) is dominant over
no freckles (f). Juan (FF) and Carolina (Ff)
have a baby.
(13). What is Juan s phenotype?
(14). What is Carolina s phenotype?
Homework Review
(16) How many boxes have FF? _____
Ff? _____ ff? ______
(17) Of the four boxes, how many show freckles?
(18) Of the four boxes, how many show no freckles?
(19) What is the probability of this couple having a
freckled baby? (give a fraction)
(20) What is the probability of this couple having a
non-freckled baby? (give a fraction)