Transcript Dihybrid Cross Notes

Dihybrid Cross Notes
Example
Heterozygous, black, hairless male mouse is
crossed with a white heterozygous hairy female
mouse.
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
Example
1. Determine
dominant and
recessive traits
Will be stated in
the problem
Black is
dominant to
white
Hairy is
dominant to
hairless
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
Example
2. Assign letters
for the trait
Dominant trait
gets the capital
letter
B = black
b = white
H = Hairy
h = hairless
Recessive traits
gets the lower
case letter
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
3. Determine Each parent
genotype for must have 4
parents
alleles
Each parent will
have has two
alleles for two
traits
Example
Heterozygous,
black, hairless male
= Bbhh
White heterozygous
hairy female = bbHh
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
4a. Draw a 4x4
square
There will be 16
boxes total
Notes
Example
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
4b. Put parent
Separate
gamete
parental alleles
combinations on
box
Think of it like
distributing
You should have
four possible
combination
Example
Bbhh gametes:
Bh, Bh, bh, bh
bbHh gametes:
bH, bh, bH, bh
Step 4b.
Bh
bH
bh
bH
bh
Bh
bh
bh
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
5. Determine
genotype of
offspring
Punnett square
holds offspring
genotypes
Genotype =
letter code
You should have
16 possible
offspring
Example
Step 5.
Bh
bH
Bh
bh
bh
BbHh BbHh bbHh bbHh
Bbhh
Bbhh
bbhh
bbhh
bh
BbHh BbHh bbHh bbHh
bH
Bbhh
bh
Bbhh
bbhh
bbhh
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
5. Determine
genotype of
offspring
Punnett square
holds offspring
genotypes
Genotype =
letter code
You should have
16 possible
offspring
Example
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
6. Determine
genotype ratio
Count offspring
in the Punnett
square
Example
4 BbHh
4 Bbhh
4 bbHh
You should have 4 bbhh
16 possible
offspring
Heterozygous, black, hairless male mouse is crossed with
a white heterozygous hairy female mouse.
Step
Notes
Example
7. Determine
phenotype
ratio
Phenotype =
what they look
like
4 Black Hairy
4 Black Hairless
4 White Hairy
4 White Hairless
You have two
traits to describe!
*ratio MUST add
up to the number
of boxes*
Genotype Practice
1. In bunnies, black is dominant to white. Rough is
dominant to smooth.
Give the genotype for each of the following:
a. Homozygous black, smooth bunny: _____________
b. Heterozygous black-rough bunny: _____________
c. White, homozygous rough bunny: _____________
d. White, smooth bunny: _____________
e. Homozygous black-rough bunny: _____________
f. White, heterozygous rough bunny: _____________
Gamete Combination Practice
2. Give the gamete combination for each genotype.
a. AATt _____, _____, _____, _____
b. AaTT _____, _____, _____, _____
c. aatt _____, _____, _____, _____
d. AAtt _____, _____, _____, _____
3. In hamsters, black coat is dominant to white coat and
rough coat is dominant to smooth coat. Two heterozygous
black-rough coated hamsters where mated.
a. Give the genotype cross: ____________x____________
b. List the possible gametes formed by each parent.
____, ____, _____, _____
3. In hamsters, black coat is dominant to white coat and
rough coat is dominant to smooth coat. Two heterozygous
black-rough coated hamsters where mated.
d. What would be the genotype ratio of the F1 generation?
___ BBRR : ___ BBRr : ___ BBrr : ___ BbRR :
___ BbRr : ___ Bbrr :
___ bbRR : ___ bbRr :
___ bbrr
e. What would be the phenotype
ratio of the F1 generation?
____ Black-Rough :
____ Black-Smooth :
____ White-Rough :
____ White-Smooth