Download Dihybrid Punnett Squares

Dihybrid Punnett Squares
What
exactly is a dihybrid cross?
Predicting
the outcomes from
crossing 2 traits.
Why
do we use them?
Instead
of doing to monohybrid
crosses, you can combine them to
see all the possible combinations
from that particular mother and
father.
Dihybrid Cross
Traits:
Seed shape & Seed color
Alleles: R round
r wrinkled
Y yellow
y green
RrYy
RY Ry rY ry
x
RrYy
RY Ry rY ry
All possible gamete combinations
Dihybrid Cross
RY
RY
Ry
rY
ry
Ry
rY
ry
Dihybrid Cross
RY
Ry
rY
RY RRYY
RRYy
RrYY
RrYy
Ry RRYy
RRyy
RrYy
Rryy
rY RrYY
ry RrYy
RrYy
Rryy
rrYY
rrYy
ry
rrYy
rryy
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
ratio
Incomplete Dominance
When
the heterozygous condition is
intermediate between dominant and
recessive
Happens because one allele is
defective, example: R=red flowers,
R’= white flowers so RR’ = pink flowers
(R codes for enzyme to produce red
pigment, R’=no enzyme)
RR x R’R’
Incomplete dominance
R’R’ x R’R’
Red
White
F1 generation: 1 Red: 2 Pink: 1 white
Codominance
Heterozygote
expresses both
alleles’ conditions
Ex.
A black rooster bred with a white
hen produces a black and white
checkered chicken.
Usually
uses both capital letters
(black= B, white=W , checkered
= BW)
Codominance practice: cross a
black rooster with a white hen
Key:
W
W
B = black
W = white
B
BW BW
BW = checkered
Results:
100% checkered
(BW)
B
BW BW
Now let’s cross a checkered hen
with a checkered rooster.
B
W
B
BB
BW
W
BW
WW
Results:
25% Black
50% Checkered
25% White
(1:2:1)
Codominance
Two
alleles are expressed (multiple
alleles) in heterozygous individuals.
Example: blood type
1.
2.
3.
4.
type
type
type
type
A
B
AB
O
=
=
=
=
IAIA or IAi
IBIB or IBi
IAIB
ii
Blood type quick facts
Red
blood cells are called
erythrocytes
Proteins on their surfaces are called
antigens, controlled by genes
Antigens make antibodies to foreign
substances, which includes RBCs with
different antigens on their surface
4 phenotypes: A, B, AB, O
3 alleles: IA, IB, i
Phenotype A
Surface molecule A
• The lA allele is
dominant to i, so
inheriting either the
lAi alleles or the lA lA
alleles from both
parents will give
you type A blood.
• Surface molecule
A is produced.
Phenotype B
• The lB allele is also
dominant to i.
• To have type B
blood, you must
inherit the lB allele
from one parent and
either another lB
allele or the i allele
from the other.
• Surface molecule B is
produced.
Surface molecule B
Phenotype AB
• The lA and lB alleles
are codominant.
• If you inherit the lA
allele from one parent
and the lB allele from
the other, your red
blood cells will produce
both surface molecules
and you will have type
AB blood.
Surface molecule B
Surface molecule A
Phenotype O
•No antigens produced
Blood
Group
Antigens
Antibodies
Can
receive
from
Can
give to
A
A
B
A or O
B
B
A
B or O
AB
A and B
None
O
None
both
A, B, AB,
O
O
A or
AB
B or
AB
AB
A, B,
AB, O
Codominance Problem
Example:homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
1/2 = IAIB
1/2 = IBi
Another Codominance Problem
Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
1/2 = IAi
1/2 = IBi