Transcript Now lets find the probability

Heredity, Genetics
Punnett Squares & Probability
Mr. Miller
Lets find out if the two pigeons on
the left produce offspring that have
the traits of the pigeon on the right
To do this we must
understand how to use a
Punnet Square
What is a Punnet Square?
• A chart that allows us to determine
the different genotypes that
offspring can inherit from their
parents
Lets see how to use it
• First we must get the genotype of each
parent
Example:
T: allele for tallness
t: allele for shortness
tt – mothers genotype
Tt – fathers genotype
Now lets set up the Punnet
Square
T
t
t
T t
t t
t
T
t
t
t
What are the number of genotypes
for the traits the offspring can
inherit?
•The offspring can
inherit two sets of
genes that will
produce a tall
phenotype
•The offspring can
inherit two sets of
genes that will
produce a short
phenotype
T
t
t
Tt
Tt
t
tt
tt
Now lets talk about
probability
What is probability?
Probability is the chance that an event will occur
How do you find the probability of an event?
You must know:
• the number of specific events
• the number of possible events
Lets find the probability the
child will be tall
How many
genotypes will
produce a tall
offspring? 2
What are number
of possible
genotypes? 4
T
t
t
Tt
tt
t
Tt
tt
Now lets find the probability!
Probability =
Number of specific event
Number of possible events
2
4
The probability of having a tall
offspring is ½, 1:2, or 50%
1
2
Now try this one
Determine the types of
genes an offspring can
inherit from parents that
have the following
genotypes:
Zz - father’s genotype
Zz - mother’s genotype
Z: gene for gray feathers
z: allele for white feathers
Z z
Z Z Z Zz
z Zz
zz
Now lets look at the possible genotypes and
the phenotypes that will be expressed
There is a single
possibility of inheriting
a homozygous (pure)
dominant genotype
which will produce a
phenotype with grey
feathers
There are two
possibilities of
inheriting
heterozygous (hybrid)
genotypes which will
produce a phenotype
with grey feathers
Z z
Z Z Z Zz
z Zz
zz
Now lets look at the possible genotypes and
the phenotypes that will be expressed
There is a single
possibility of inheriting
a homozygous (pure)
recessive genotype
which will produce a
phenotype with white
feathers
So two grey birds can
produce a pigeon with
white feathers!
Z z
Z Z Z Zz
z Zz
zz
Now lets find the probability
Lets find the
probability the
offspring will have
grey feathers.
number of specific events
number of possible events
Z
z
Z
ZZ
Zz
z
Zz
zz
3
=4
Now lets find the probability
Lets find the
probability the
offspring will have
white feathers.
number of specific events
number of possible events
Z
z
Z
ZZ
Zz
z
Zz
zz
1
=4