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: