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Dihybrid Crosses

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Dihybrid Crosses Biology 30 Mrs. S. Pipke-Painchaud Dihybrid Crosses the natural progression for Mendel was to study 2 characteristics at the same time. – PowerPoint PPT presentation

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Title: Dihybrid Crosses


1
Dihybrid Crosses
  • Biology 30
  • Mrs. S. Pipke-Painchaud

2
Dihybrid Crosses
  • the natural progression for Mendel was to study 2
    characteristics at the same time.
  • thus, the study of 2 pairs of contrasting traits
    at the same time a dihybrid cross
  • ex.. round yellow seeds X wrinkled green seeds

3
Mendels Fourth Law
  • The Law of Independent Assortment
  • During gamete formation, segregating pairs of
    unit factors assort independently of each other.
  • the two traits are inherited totally
    independently of each other.
  • i.e. color is inherited independently of seed
    shape.
  • Example
  • Homozygous round green X wrinkled homozygous
    yellow

4
Solving Dihybrid Crosses
  • Follow the steps
  • If you were to cross a Homozygous round green X
    wrinkled homozygous yellow plant, what would your
    phenotypic and genotypic ratios be?

5
Step 1 Make a Key.
  • G yellow
  • g green
  • W round
  • w wrinkled

6
Step 2 Give the genotypes of the parents. . .
  • Homozygous round green X wrinkled homozygous
    yellow plant
  • P1 WWgg X wwGG

7
Step 3 Determine the Gametes . . .
  • WWgg X wwGG
  • WWgg Wg, Wg, Wg, Wg
  • wwGG wG, wG, wG, wG
  • HINT Foil to get the gametes

8
Step 4 Fill in the Punnett square . . .
Wg Wg Wg Wg
wG WwGg WwGg WwGg WwGg
wG WwGg WwGg WwGg WwGg
wG WwGg WwGg WwGg WwGg
wG WwGg WwGg WwGg WwGg
9
Step 5 Answer any questions . . .
  • Genotypic ratio
  • all WwGg
  • Phenotypic ratio
  • all round yellow

G yellow g green W round w wrinkled
10
F1 X F1 WwGg X WwGg
  • Remember to determine the gametes for your
    punnett square.

WwGg X WwGg
11
Fill in the Punnett Square
WG Wg wG wg
WG WWGG WWGg WwGG WwGg
Wg WWGg WWgg WwGg Wwgg
wG WwGG WwGg wwGG wwGg
wg WwGg Wwgg wwGg wwgg
Do you see a pattern?
12
The PATTERN . . .
WG Wg wG wg
WG WWGG WWGg WwGG WwGg
Wg WWGg WWgg WwGg Wwgg
wG WwGG WwGg wwGG wwGg
Wg WwGg Wwgg wwGg wwgg
13
What are the ratios?
  • Genotypic Ratio
  • 1 WWGG
  • 2 WWGg
  • 1 WWgg
  • 2 WwGG
  • 4 WwGg
  • 2 Wwgg
  • 1 wwGG
  • 2 wwGg
  • 1 wwgg

WG Wg wG wg
WG WWGG WWGg WwGG WwGg
Wg WWGg WWgg WwGg Wwgg
wG WwGG WwGg wwGG wwGg
Wg WwGg Wwgg wwGg wwgg
14
Phenotypic Ratio
G yellow g green W round w wrinkled
  • Phenotypic Ratio
  • 9 Yellow Round
  • Dominant Dominant
  • 3 Yellow Wrinkled
  • Dominant Recessive
  • 3 Green Round
  • Recessive Dominant
  • 1 Green Wrinkled
  • Recessive Recessive
  • Genotypic Ratio
  • 1 WWGG
  • 2 WWGg
  • 1 WWgg
  • 2 WwGG
  • 4 WwGg
  • 2 Wwgg
  • 1 wwGG
  • 2 wwGg
  • 1 wwgg

Explain the patterns
15
The Short Cut
  • can only be used if you have
  • (Big little Big little X Big little Big little)
  • BbTt x BbTt
  • Do these fit?
  • BBTt X BbTt
  • BbTt x Bb tt

16
Try this
  • C Inflated Pod c constricted pod
  • D Tall d dwarf
  • The cross a plant heterozygous for inflated pod
    and heterozygous tall is crossed with a another
    heterozygous inflated pod and heterozygous tall
    plant. What are the genotypic and phenotypic
    ratios?
  • The parents are
  • CcDd x CcDd

17
Example
C Inflated Pod c constricted pod D Tall d
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
  • CcDd x CcDd
  • Does this fit the short cut?
  • Yes

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
18
Now try . . .
  • Refer to the assigned questions in your duotang.
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