Warm-up Turn in your meiosis simulation activity and your punnett piggy activity sheets.
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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.
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?
Step 1
Draw a box and divide it into 16 squares.
Step 2
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
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 First- YR Outside- Yr Inside- yR Last- yr
Principle of independent Assortment!
Step 4
Write all of the possible combinations of alleles on the sides and top of the punnett square. YR Yr yR yr
YR
YR
Yr
Yr
yR
yR
yr
yr
Step 5
Do the cross Remember to keep all of
one letter together and all of the 2nd letter together.
YR
YR
Yr
Yr
yR
yR
yr
yrYYRR YYRr
YYRr YYrr
YyRR
YyRr Yyrr
YyRr
YyRR
YyRr
yyRR
yyRr yyrr
yyRr
Yyrr
YyRr
Step 6
Go through the results and determine what the phenotype of each offspring would be
YR
YR
Yr
Yr yR
yr
yrYYRR
Yellow round
YYRr
Yellow, round
YYRr
Yellow, round
YYrr
Yellow,wrinkled
YyRR
Yellow, round
YyRr
Yellow, round
Yyrr
Yellow, wrinkled
YyRr
Yellow, round
YyRR
Yellow, round
YyRr
Yellow, round
yyRR
Green, round
yyRr
Green, round
Yyrr
Green, wrinkled
yyRr
Green, round
Yyrr
Yellow, wrinkled
YyRr
Yellow, round
yR
Step 7
Figure out the phenotypic ratio or answer whatever question they ask you. 9:3:3:1
Example: what are the chances of having a yellow and wrinkled pea? 3/16
YR
YR
Yr
Yr yR
yr
yrYYRR
Yellow round
YYRr
Yellow, round
YYRr
Yellow, round
YYrr
Yellow, wrinkled
YyRR
Yellow, round
YyRr
Yellow, round
Yyrr
Yellow, wrinkled
YyRr
Yellow, round
YyRR
Yellow, round
YyRr
Yellow, round
yyRR
Green, round
yyRr
Green, round
Yyrr
Green, wrinkled
yyRr
Green, round
Yyrr
Yellow, wrinkled
YyRr
Yellow, round
yR
Incomplete Dominance
Heterozygous offspring show a phenotype that is in between the phenotypes of the two homozygous parents
Incomplete Dominance
R R
W
W
RW RW
RW RW
Crossing homozygous parents to produce F1
generation
THE ALLELES REMAIN DISTINCT; ONLY THE PHENOTYPE APPEARS BLENDED.
CodominanceBoth 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 DominanceTraits are blended
(red + white = pink)
CodominanceBoth traits are
expressed (A + B = AB)
Multiple AllelesA 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
Multiple AllelesMore than two
possible alleles, but only two present at a
time.
Polygenic TraitSingle trait
controlled by more than one
gene.
In summary:
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