Dihybrid CrossesDihybrid Crosses

Biology 30 Biology 30 Mrs. S. Pipke-PainchaudMrs. S. Pipke-Painchaud

Dihybrid CrossesDihybrid Crosses the natural progression for Mendel was to the natural progression for Mendel was to

study 2 characteristics at the same time.study 2 characteristics at the same time.

thus, the study of 2 pairs of contrasting thus, the study of 2 pairs of contrasting traits at the same time = a dihybrid crosstraits at the same time = a dihybrid cross

ex.. round yellow seeds X wrinkled green seedsex.. round yellow seeds X wrinkled green seeds

Mendel’s Fourth LawMendel’s Fourth Law The Law of Independent AssortmentThe Law of Independent Assortment

During gamete formation, segregating pairs of During gamete formation, segregating pairs of unit factors assort independently of each other.unit factors assort independently of each other. the two traits are inherited totally independently of the two traits are inherited totally independently of

each other.each other. i.e. color is inherited independently of seed shape.i.e. color is inherited independently of seed shape. ExampleExample::

Homozygous Homozygous roundround green X green X wrinkledwrinkled homozygous yellow homozygous yellow

Solving Dihybrid CrossesSolving Dihybrid Crosses Follow the steps Follow the steps

If you were to cross a If you were to cross a Homozygous Homozygous roundround green X green X wrinkledwrinkled homozygous homozygous yellow plant, what would your phenotypic yellow plant, what would your phenotypic and genotypic ratios be?and genotypic ratios be?

Step 1: Make a Key….Step 1: Make a Key….

G= yellowG= yellow g = greeng = green W = roundW = round w = wrinkledw = wrinkled

Step 2: Give the genotypes of Step 2: Give the genotypes of the parents. . . the parents. . .

Homozygous Homozygous roundround green X green X wrinkledwrinkled homozygous yellow planthomozygous yellow plant

P1 = WWgg X wwGGP1 = WWgg X wwGG

Step 3: Step 3: Determine the Gametes . . . Determine the Gametes . . .

WWgg X wwGGWWgg X wwGG

WWgg = Wg, Wg, Wg, WgWWgg = Wg, Wg, Wg, Wg

wwGG = wG, wG, wG, wGwwGG = wG, wG, wG, wGHINT: Foil to get the gametesHINT: Foil to get the gametes

Step 4: Step 4: Fill in the Punnett square . . .Fill in the Punnett square . . .

WgWg WgWg WgWg WgWg

wGwG WwGgWwGg WwGgWwGg WwGgWwGg WwGgWwGg

wGwG WwGgWwGg WwGgWwGg WwGgWwGg WwGgWwGg

wGwG WwGgWwGg WwGgWwGg WwGgWwGg WwGgWwGg

wGwG WwGgWwGg WwGgWwGg WwGgWwGg WwGgWwGg

Step 5: Step 5: Answer any questions . . .Answer any questions . . .

Genotypic ratio Genotypic ratio = all WwGg= all WwGg

Phenotypic ratio Phenotypic ratio = all round yellow= all round yellow

G= yellowG= yellowg = greeng = greenW = roundW = roundw = wrinkledw = wrinkled

F1 X F1F1 X F1 = WwGg X = WwGg X WwGgWwGg Remember to determine the gametes for your Remember to determine the gametes for your

punnett square.punnett square.

Fill in the Punnett SquareFill in the Punnett SquareWGWG WgWg wGwG wgwg

WGWG WWGGWWGG WWGgWWGg WwGGWwGG WwGgWwGg

WgWg WWGgWWGg WWggWWgg WwGgWwGg WwggWwgg

wGwG WwGGWwGG WwGgWwGg wwGGwwGG wwGgwwGg

wgwg WwGgWwGg WwggWwgg wwGgwwGg wwggwwgg

The PATTERN . . . The PATTERN . . .

WGWG WgWg wGwG wgwg

WGWG WWWWGGGG WWWWGgGg WwWwGGGG WwWwGgGg

WgWg WWWWGgGg WWWWgggg WwWwGgGg WwWwgggg

wGwG WwWwGGGG WwWwGgGg wwwwGGGG wwwwGgGg

WgWg WwWwGgGg WwWwgggg wwwwGgGg wwwwgggg

What are the ratios?What are the ratios? Genotypic Ratio:Genotypic Ratio:

1 WWGG1 WWGG 2 WWGg2 WWGg 1 WWgg1 WWgg 2 WwGG2 WwGG 4 WwGg4 WwGg 2 Wwgg2 Wwgg 1 wwGG1 wwGG 2 wwGg2 wwGg 1 wwgg1 wwgg

WGWG WgWg wGwG wgwg

WGWG WWGGWWGG WWGgWWGg WwGGWwGG WwGgWwGg

WgWg WWGgWWGg WWggWWgg WwGgWwGg WwggWwgg

wGwG WwGGWwGG WwGgWwGg wwGGwwGG wwGgwwGg

WgWg WwGgWwGg WwggWwgg wwGgwwGg wwggwwgg

Phenotypic Ratio:Phenotypic Ratio: Phenotypic Ratio:Phenotypic Ratio:

9 Yellow Round9 Yellow Round Dominant DominantDominant Dominant

3 Yellow Wrinkled3 Yellow Wrinkled Dominant RecessiveDominant Recessive

3 Green Round3 Green Round Recessive DominantRecessive Dominant

1 Green Wrinkled1 Green Wrinkled Recessive RecessiveRecessive Recessive

Genotypic Ratio:Genotypic Ratio: 1 WWGG1 WWGG 2 WWGg2 WWGg 1 WWgg1 WWgg 2 WwGG2 WwGG 4 WwGg4 WwGg 2 Wwgg2 Wwgg 1 wwGG1 wwGG 2 wwGg2 wwGg 1 wwgg1 wwgg

G= yellowG= yellowg = greeng = greenW = roundW = roundw = wrinkledw = wrinkled

** Explain the patterns

The Short Cut:The Short Cut:

can only be used if you have can only be used if you have (Big little Big little X Big little Big little)(Big little Big little X Big little Big little)

BbTt x BbTtBbTt x BbTt

Do these fit?Do these fit? BBTt X BbTtBBTt X BbTt BbTt x Bb ttBbTt x Bb tt

Try this:Try this:

C= Inflated PodC= Inflated Pod c = constricted podc = constricted podD = TallD = Tall d = dwarfd = dwarf The cross:The cross: a plant heterozygous for inflated a plant heterozygous for inflated

pod and heterozygous tall is crossed with a pod and heterozygous tall is crossed with a another heterozygous inflated pod and another heterozygous inflated pod and heterozygous tall plant. What are the heterozygous tall plant. What are the genotypic and phenotypic ratios?genotypic and phenotypic ratios? The parents are:The parents are:

CcDd x CcDdCcDd x CcDd

Example:Example: CcDd x CcDdCcDd x CcDd Does this fit the Does this fit the

short cut?short cut? YesYes

C= Inflated PodC= Inflated Podc = constricted podc = constricted podD = TallD = Talld = dwarfd = dwarf

Genotypic Ratio:

1

2

1

2

4

2

1

2

1

Genotypic Ratio:

1 CCDD

2 CCDd

1 CCdd

2 CcDD

4 CcDd

2 Ccdd

1 ccDD

2 ccDd

1 ccdd

Phenotypic Ratio:

(D) (D)

9

(D) ®

3

® (D)

3

® ®

1

Phenotypic Ratio:

(D) (D)

9 Inflated Tall

(D) ®

3 Inflated Dwarf

® (D)

3 Constricted Tall

® ®

1 Constricted Dwarf

Now try . . .Now try . . . Refer to the assigned questions in your Refer to the assigned questions in your

duotang.duotang.