Transcript Dihybrid Cross

BELL WORK:
• In pigeons, ash-red feathers (B) are
dominant to blue feathers (b).
• A heterozygous pigeon is crossed with a
homozygous recessive pigeon. What
percent of the offspring will have ash-red
feathers?
• You do not have to copy the question,
but you must complete a Punnett
square!
B
b
b
Bb
bb
b
Bb
bb
HOMEWORK!!
Tonight’s homework:
answer questions on the worksheet
as you watch the video (same video
as the last homework).
CO: I will predict genetic
outcomes using dihybrid
crosses.
LO: I will write notes and
practice dihybrid crosses.
A Dihybrid Cross shows the
possible offspring for two traits
Fur Color:
B: Black
b: White
Coat Texture:
R: Rough
r: Smooth
In this example, we will cross a
heterozygous individual with another
heterozygous individual. Their
genotypes will be:
BbRr x BbRr
Dihybrid Cross
BbRr x BbRr
Step 1: Find ALL possible gametes that can
be made from each parent.
Remember, each gamete must have one B
and one R.
Dihybrid Cross
BbRr x BbRr
Possible gametes:
BR
Step 2: Arrange all possible
Br
gametes for one parent on
the top of your Punnett
bR
Square and the other parent
br
on the side
Dihybrid Crosses:
a cross that shows the possible offspring for two traits
BbRr x BbRr
Fur Color:
B: Black
b: White
Coat Texture:
R: Rough
r: Smooth
Step 3: Fill in the
Punnett Square
(find the possible
genotypes of the
offspring)
BR
BR
Br
bR
br
Br
bR
br
Dihybrid Crosses:
a cross that shows the possible offspring for two traits
BR
Br
bR
br
BR
BBRR
BBRr
BbRR
BbRr
Br
BBRr
BBrr
BbRr
Bbrr
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
BbRr x BbRr
Fur Color:
B: Black
b: White
Coat Texture:
R: Rough
r: Smooth
How many of the
offspring would have a
black, rough coat?
How many of the
offspring would have a
black, smooth coat?
How many of the
offspring would have a
white, rough coat?
How many of the
offspring would have a
white, smooth coat?
BR
Br
bR
br
BR BBRR
BBRr
BbRR
BbRr
Br
BBRr
BBrr
BbRr
Bbrr
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
Fur Color:
Coat Texture:
B: Black
R: Rough
b: White
r: Smooth
How many of the
offspring would have
black, rough coat?
How many of the
offspring would have a
black, smooth coat?
How many of the
offspring would have a
white, rough coat?
How many of the
offspring would have a
white, smooth coat?
BR
Br
bR
br
BR BBRR
BBRr
BbRR
BbRr
Br
BBRr
BBrr
BbRr
Bbrr
bR
BbRR
BbRr
bbRR
bbRr
br
BbRr
Bbrr
bbRr
bbrr
Phenotypic Ratio=
9:3:3:1
Fur Color:
Coat Texture:
B: Black
R: Rough
b: White
r: Smooth
Mendelian Genetics
Review
Walk around the room and answer
the review questions with a partner
or by yourself.
You do NOT have to write the
question, but you MUST write the
question NUMBER!
Practice in your notes…
In pea plants, yellow seeds (Y) are dominant over
green seeds (y), and rounded peas (R) are
dominant over wrinkled peas (r).
Cross (what do you have to draw?) a plant that is
heterozygous for both traits with a plant that is
homozygous recessive for both traits. Draw a
Punnett square to show all possible offspring,
and determine the genotypic and phenotypic
ratios.