Transcript Dihybrid Crosses - Kent City School District

Mendel’s peas
Character
Seed shape
Seed color
© 2007 Paul Billiet ODWS
Trait
Allele
Round
R
Wrinkled
r
Yellow
Y
Green
y
Combinations
Genotype
RRYY
RRYy
RrYY
RrYy
RRyy
Rryy
rrYY
rrYy
rryy
© 2007 Paul Billiet ODWS
Phenotype
Round Yellow
Round Yellow
Round Yellow
Round Yellow
Round Green
Round Green
Wrinkled Yellow
Wrinkled Yellow
Wrinkled Green
THE LAW OF INDEPENDENT
ASSORTMENT
 It appears that the inheritance of seed shape has
no influence over the inheritance of seed color
 The two traits are inherited INDEPENDENTLY
 The pairs of alleles that control these two traits
assort themselves independently
© 2007 Paul Billiet ODWS
Mendel & Meiosis
 The pairs of chromosomes could orientate in
different ways at Anaphase 1
© 2007 Paul Billiet ODWS
Dihybrid cross genetic diagram
P
Phenotypes Round Yellow
seed
Genotypes
Gametes
X
Wrinkled
Green seed
RRYY
rryy
meiosis
meiosis
RY
ry
fertilization
F1 Phenotypes
RrYy
Genotypes
Round Yellow
Proportions
100%
© 2007 Paul Billiet ODWS
(Pure bred)
When working with Dihybrid
Crosses we use the FOIL method
Example of a Dihybrid Genotype
Bb CC
First
BC
Outside
Inside
Last
BC
bC
bC
Examples of FOIL- Use these
parental genotypes to find the
possible gametes:
1.
2.
3.
4.
5.
RrTt
RRTT
rrTt
RRTt
Rrtt
No need to repeat gametes if they are
the same…pay close attention!
In mice, running is dominant to waltzing, and black
coat color is dominant to white. Use a punnet square
to predict the results of a cross between a
heterozygous running, white mouse and a waltzing,
heterozygous black mouse.
*First we need to FOIL out the genotypes
____ ____, ____ ____ X ____ ____, ____ ____
F:
F:
O:
O:
I:
I:
L:
L:
Solving a Dihybrid
 Create your dihybrid cross [4x4]
Solving a Dihybrid
 Determine Genotype Ratios
 record all genotypes you have
 count and record number of each genotype
 RrBb
 rrBb
 Rrbb
 rrbb
Rb
Rb
rb
rb
rB
RrBb
RrBb
rrBb
rrBb
rb
Rrbb
Rrbb
rrbb
rrbb
rB
RrBb
RrBb
rrBb
rrBb
rb
Rrbb
Rrbb
rrbb
rrbb
Solving a Dihybrid
 Determine Phenotype Ratios
 count how many of each phenotype you have
 record # of phenotypes represented