Download Genetics Day 2 Punnett Squares

Genetics
Notes Day 2
Warm Up – What is the difference
between a genotype and a
phenotype? Give an example of
each.
We are doing “Throw Back
Thursday” this week!
Bring in your
PHOTOS!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
A diagram that predicts the
expected outcome of a genetic
cross.
Punnett Squares
Helps you keep
track of traits.
Punnett Squares
.
Dominant and recessive alleles
are represented by letters.
Punnett Squares
A capital letter (T) is used for
dominant alleles.
Punnett Squares
A lowercase letter (t) is
used for recessive alleles.
Example (Tall or short)


T = dominant allele
Homozygous dominant
–

Phenotype = __________
Heterozygous
–

Genotype = _____
t = recessive allele
Genotype = _____
Phenotype = __________
Homozygous recessive
–
Genotype = _____
Phenotype = __________
Punnett Squares
If you wanted to know the type of offspring
a cross between two parents would
produce, you can use a punnett square.
Tt x Tt
TT,Tt for tall
Tt for short
Punnett Squares
The letters representing the alleles from
one parent are placed along the top of the
square.
T
t
Punnett Squares
The letters representing the two alleles from the second
Parent are places along the side of the square.
T
t
Punnett Squares
T t xT t
T
T
t
t
Punnett Squares
Squares are filled by writing the letter at the
top beside the letter on the side.
T
T
TT
t
Tt
t
Tt
tt
Punnett Squares
The letters in each of the squares
represents the Genotypes of the offspring
that the parents could produce.
T
T
TT
t
Tt
t
Tt
tt
TT
Tt
Tt
tt
Punnett Squares
The genotype (genetic makeup)
can be used to predict the
phenotype (physical appearance)
of the offspring.
Punnett Sqaures
Genotype
TT
Tt
Tt
tt
Phenotype
tall
tall
tall
short
Punnett Squares
Probability: the ratio that a
particular event could occur.
3 would be tall
out of 4 offspring
1 would be short
Punnett Squares:
•Help you keep track of traits.
•Predict genotype and phenotype.
•Calculate probability.
BB x bb
b
B
B
Bb
Bb
b
Bb
Bb
Genotypes: Bb, Bb, Bb, Bb
Phenotypes: All brown
Probability: 100%
BB x Bb
B
B
B
BB
BB
b
Bb
Bb
Genotypes: BB, BB, Bb, Bb
Phenotypes: All brown
Probability: 100% brown
Genetics Notes Day 3

Warm Up: Create a Monohybrid cross from
these parents:
Dad = heterozygous for Brown Eyes
Mom = homozygous recessive for Blue
Eyes
b
b
B
b
Bb
bb
Bb
bb
Dihybrid Crosses

A cross that involves two pairs of contrasting
traits.
–
RrYy
–
RY
RY
–
crossed with
Ry
Ry
rY
rY
ry
ry
RrYy
BBff
x BBFF
• Bf
Bf
Bf
Bf
• BF
BF
BF
BF
Ttrr
x
ttRr
• Tr
Tr
tr
tr
• tR
tr
tR
tr