Transcript How to make a punnett square

Warm-up
Turn in your meiosis simulation activity and
your punnett piggy activity sheets
Dihybrid crosses
Dihybrid crosses are punnett squares used
to predict the probability of an offspring
having 2 traits at the same time.
 Ex: What are the chances of my baby
having brown eyes AND blond hair.
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Dihybrid crosses
Yellow seeds (Y) are dominant to green
seeds (y)
 Round seeds (R) are dominant to wrinkled
seeds (r)
 If both parents are heterozygous for both
traits, what are the genotypic and phenotypic
ratios of the offspring?
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Step 1
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Draw a box and divide
it into 16 squares.
Step 2
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Determine the
genotypes of the
parents
YyRr x YyRr
Ex: cross two pea
plants that are
heterozygous for
yellow peas and round
peas.
Yellow is dominant to
green and round is
dominant to wrinkled.
Step 3
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Determine all of the
possible gamete
combinations for each
parent by using the
F.O.I.L. method
FOIL= first, outside,
inside last
Ex: YyRr
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First- YR
Outside- Yr
Inside- yR
Last- yr
Principle of independent Assortment!
Step 4
YR
Write all of the possible
combinations of alleles
on the sides and top of
the punnett square.
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YR
Yr
yR
yr
YR
Yr
yR
yr
Yr
yR
yr
Step 5
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Do the cross
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Remember to keep all of YR
one letter together and
all of the 2nd letter
Yr
together.
yR
yr
YR
Yr
yR
yr
YYRR
YYRr
YyRR
YyRr
YYRr
YYrr
YyRr
Yyrr
YyRR
YyRr
yyRR
yyRr
YyRr
Yyrr
yyRr
yyrr
Step 6
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Go through the results
and determine what the YR
phenotype of each
offspring would be
Yr
yR
yr
YR
Yr
yR
yr
YYRR
YYRr
YyRR
YyRr
Yellow
round
Yellow,
round
Yellow,
round
Yellow,
round
YYRr
YYrr
YyRr
Yyrr
Yellow,
round
Yellow,w
rinkled
Yellow,
round
Yellow,
wrinkled
YyRR
YyRr
yyRR
yyRr
Yellow,
round
Yellow,
round
Green,
round
Green,
round
YyRr
Yyrr
yyRr
Yyrr
Yellow,
round
Yellow,
wrinkled
Green,
round
Green,
wrinkled
Step 7
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Figure out the
phenotypic ratio or
YR
answer whatever
question they ask you.
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9:3:3:1
Yr
Example: what are the
yR
chances of having a
yellow and wrinkled
yr
pea?
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3/16
YR
Yr
yR
yr
YYRR
YYRr
YyRR
YyRr
Yellow
round
Yellow,
round
Yellow,
round
Yellow,
round
YYRr
YYrr
YyRr
Yyrr
Yellow,
round
Yellow,
wrinkled
Yellow,
round
Yellow,
wrinkled
YyRR
YyRr
yyRR
yyRr
Yellow,
round
Yellow,
round
Green,
round
Green,
round
YyRr
Yyrr
yyRr
Yyrr
Yellow,
round
Yellow,
wrinkled
Green,
round
Green,
wrinkled
Incomplete Dominance

Heterozygous offspring show a phenotype that
is in between the phenotypes of the two
homozygous parents
Incomplete Dominance
R
R
W
RW
RW
W
RW
RW
Crossing homozygous parents to produce F1 generation
THE ALLELES REMAIN DISTINCT; ONLY THE
PHENOTYPE APPEARS BLENDED.
Codominance
Both alleles in the heterozygote
express themselves fully.
Example: Blood types
Roan cattle
Codominance
A person
homozygous for
Type A blood
And a person
homozygous for
Type B blood
Will produce a child
that will demonstrate
both Type A and Type
B blood (Type AB)
Summary
Incomplete Dominance
Codominance
Traits are blended
(red + white = pink)
Both traits are
expressed
(A + B = AB)
Multiple Alleles
A gene that has more than
two possible alleles, though
only two alleles are present
at a time.
EX: Blood Type
A, B, O
Polygenic Traits
Polygenic Traits- Traits controlled by two or
more genes that interact.
 Ex: Human Eye Color and skin pigment
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In summary:
Multiple Alleles
Polygenic Trait
More than two
possible alleles,
but only two
present at a
time.
Single trait
controlled by
more than one
gene.