Trihybrid crossTrihybrid crossTrihybrid crossTrihybrid cross

More complex by “easily” calculated following principles of segregation,

independent assortment and probability

More complex by “easily” calculated following principles of segregation,

independent assortment and probability

PUNNETT SQUARE HAS 64 PUNNETT SQUARE HAS 64 BOXES…BOXES…DEMONSTRATES THAT DEMONSTRATES THAT MENDEL’S PRINCIPLES MENDEL’S PRINCIPLES APPLY TO INHERITANCE OF APPLY TO INHERITANCE OF MULTIPLE TRAITSMULTIPLE TRAITS

PUNNETT SQUARE HAS 64 PUNNETT SQUARE HAS 64 BOXES…BOXES…DEMONSTRATES THAT DEMONSTRATES THAT MENDEL’S PRINCIPLES MENDEL’S PRINCIPLES APPLY TO INHERITANCE OF APPLY TO INHERITANCE OF MULTIPLE TRAITSMULTIPLE TRAITS

Trihybrid crossTrihybrid cross

Trihybrid crossesTrihybrid crossesTrihybrid crossesTrihybrid crosses

The basic concepts are the same as with mono- or dihybrid crosses

Just remember:• each gamete must have ONE COPY OF EACH

GENE• random segregation and independent

assortment still apply

The basic concepts are the same as with mono- or dihybrid crosses

Just remember:• each gamete must have ONE COPY OF EACH

GENE• random segregation and independent

assortment still apply

Trihybrid crossesTrihybrid crossesTrihybrid crossesTrihybrid crosses

• The basic concepts are the same as with mono- or dihybrid crosses

• Just remember:• each gamete must have ONE COPY OF EACH

GENE• random segregation and independent assortment

still apply

• The basic concepts are the same as with mono- or dihybrid crosses

• Just remember:• each gamete must have ONE COPY OF EACH

GENE• random segregation and independent assortment

still apply

Trihybrid crossesTrihybrid crossesTrihybrid crossesTrihybrid crosses

• tall, pinched pod, axial X dwarf, inflated, terminal

• TT pp AA tt PP aa

• F1: tall, inflated, axial

•

•

• tall, pinched pod, axial X dwarf, inflated, terminal

• TT pp AA tt PP aa

• F1: tall, inflated, axial

•

•

Tt Pp Aa

F1 X F1 --> ?

Trihybrid crossesTrihybrid crossesTrihybrid crossesTrihybrid crosses

• Step one: Figure out the gametes produced by each parent (use 2n)• Parents: Tt Pp Aa; 23 = 8

• eight possible gametes from each parent:• TPA TPa TpA tPA

Tpa tPa tpA tpa

• Step one: Figure out the gametes produced by each parent (use 2n)• Parents: Tt Pp Aa; 23 = 8

• eight possible gametes from each parent:• TPA TPa TpA tPA

Tpa tPa tpA tpa

Forked-line MethodForked-line MethodForked-line MethodForked-line Method

• Breaks down multi-hybrid crosses into a series of monohybrid crosses

• Combine the individual ratios (multiply) to get the final ratio

• Breaks down multi-hybrid crosses into a series of monohybrid crosses

• Combine the individual ratios (multiply) to get the final ratio

Forked-line MethodForked-line MethodForked-line MethodForked-line Method

Tt Pp Aa X Tt Pp Aa

Break into Tt X Tt; Pp X Pp; Aa X Aa

• Tt X Tt --> 3/4 T: 1/4 t• Pp X Pp --> 3/4 P: 1/4 p• Aa X Aa --> 3/4 A: 1/4 a

Tt Pp Aa X Tt Pp Aa

Break into Tt X Tt; Pp X Pp; Aa X Aa

• Tt X Tt --> 3/4 T: 1/4 t• Pp X Pp --> 3/4 P: 1/4 p• Aa X Aa --> 3/4 A: 1/4 a

Forked lineForked lineForked lineForked line

F2 offspring:F2 offspring:

3/4 T

1/4 t

<3/4 P

1/4 p

<3/4 P

1/4 p

<3/4 A

1/4 a

3/4 A

1/4 a

<3/4 A

1/4 a

<3/4 A

1/4 a

--> 27/64 TPA

--> 9 /64 TPa

--> 9 /64 TpA

--> 3 /64 Tpa

--> 9 /64 tPA

--> 3 /64 tPa

--> 3 /64 tpA

--> 1 /64 tpa

Forked-lineForked-lineForked-lineForked-line

• Can find genotypic ratios

• substitute 1/4 TT; 1/2 Tt; 1/4 tt, etc.

• Can go straight to one phenotype or genotype

• ignore all branches except those leading to the desired

phenotype or genotype

• Can find genotypic ratios

• substitute 1/4 TT; 1/2 Tt; 1/4 tt, etc.

• Can go straight to one phenotype or genotype

• ignore all branches except those leading to the desired

phenotype or genotype

Trihybrid Trihybrid CrossCrossTrihybrid Trihybrid CrossCross

The Principle of Independent The Principle of Independent AssortmentAssortmentThe Principle of Independent The Principle of Independent AssortmentAssortment

• Factors for different traits assort independently of one another• Genes are inherited

independently of each other

• Segregate randomly in gametes

• Dihybrid Cross

• Factors for different traits assort independently of one another• Genes are inherited

independently of each other

• Segregate randomly in gametes

• Dihybrid Cross

Branch Diagram of Dihybrid CrossBranch Diagram of Dihybrid CrossBranch Diagram of Dihybrid CrossBranch Diagram of Dihybrid CrossPhenotype

Genotype vs. Genotype vs. PhenotypePhenotypeGenotype vs. Genotype vs. PhenotypePhenotype