Imagine in the future…
when something like THIS
could be possible…
On a clean sheet of paper, write down what you think is happening in
these pictures and how it makes you feel
The future is now…
WELCOME TO
GENETICS!!!
GENETICS
the study of how
traits are passed from
one generation to the
next
How can we
determine what the
offspring are going
to be?
PUNNETT
SQUARES
Reginald C. Punnett
• Inventor of the
Punnett Square
PUNNETT
SQUARES
charts showing the
possible combinations
of alleles in a cross
Punnett Squares
show the
probability of
getting a certain
type of offspring
PROBABILTY
is the chance that
an event will occur
PUNNETT SQUARES
Each square shows the chance of
getting a baby with that genotype
If there are
4 squares,
what
percent is
each square
worth?
THE PARENTS
GENOTYPES
• DAD = Tt (heterozygous)
• MOM = Tt (heterozygous)
PHENOTYPES
• DAD = Tall
• MOM = Tall
PUNNETT SQUARES
One parent’s genes go across the top
(one per box)
The other
parent’s
genes go
down the
side (one
per box)
PUNNETT SQUARES
Each letter goes into each box below it
Each letter
goes into
each box
next to it
PUNNETT SQUARES
Now we can predict the possibility that the
parents will have a baby with that kind of
phenotype
PUNNETT SQUARES
What is the possibility that the parents will
have a tall baby?
TT = tall
25%
Tt = tall
50%
So 75%
chance
PUNNETT SQUARES
What is the possibility that the parents will
have a short baby?
tt = short
25%
So 25%
chance
THE OFFSPRING
GENOTYPES
1TT:2Tt:1tt (1:2:1)
25% TT, 50% Tt, 25% tt
•
•
•
•
TT (homozygous dominant)
Tt (heterozygous)
Tt (heterozygous)
tt (homozygous recessive)
THE OFFSPRING
PHENOTYPES
3 Tall :1 Short (3:1)
75% Tall, 25% Short
•
•
•
•
TT (tall)
Tt (tall)
Tt (tall)
tt (short)
Cross a homozygous
dominant with a recessive
(for height where T is
dominant and tall).
Find the percent chance of
each genotype and each
phenotype
Cross a heterozygote with a
recessive (for height where T
is dominant and tall).
Find the percent chance of
each genotype and each
phenotype
Sex Linked Trait
a trait that is found
on either the X or Y
chromosome
Hemophilia is an
example of a sex
linked trait.
Hemophilia
a disease where your
blood does not clot.
Hemophilia only
occurs when all of the
X chromosomes have a
copy of the recessive
gene.
H
h
X X :female carrier
h
h
X X :female hemophiliac
H
X Y:normal male
h
X Y:hemophiliac male
INDEPENDENT
ASSORTMENT
Alleles will separate
independently. They don’t
stick together.
Why Did Mendel Conclude That
The Inheritance of one Trait is
Independent of Another?
The
alternative
and
incorrect
hypothesis:
dependent
inheritance
.
Because it’s the only way to explain
the pattern of inheritance.
Dihybrid cross
A cross of two hybrid traits
As example:
RrYy x RrYy
R= round r = wrinkled
Y=yellow y= green
Dihybrid cross
RrYy
Each allele gets paired up with
each of the other alleles.
Possible combinations:
Dihybrid cross
RrYy x RrYy
Arrange the punnett square the same way.
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Dihybrid cross
How much is each square worth now?
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
PHENOTYPES
9 round and yellow :3 wrinkled
and yellow: 3 round and green: 1
wrinkled and green (9:3:3:1)
•
•
•
•
•
•
•
•
RRYY (Round and yellow) - 1
RrYY (Round and yellow) – 2
RRYy (Round and yellow) - 2
RrYy (Round and yellow) - 4
Rryy (Round and green) - 3
rrYy (wrinkled and Yellow) - 1
rrYY (wrinkled and Yellow) - 2
Rryy (wrinkled and green) - 1