genetic

1. Trihybrid cross
Trihybrid cross
More complex by “easily” calculated
More complex by “easily” calculated
following principles of segregation,
following principles of segregation,
independent assortment and
independent assortment and
probability
probability

2. Trihybrid cross
Trihybrid cross
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 TRAITS
MULTIPLE TRAITS

3. Trihybrid crosses
Trihybrid crosses
The basic concepts are the same as with mono- or
The basic concepts are the same as with mono- or
dihybrid crosses
dihybrid crosses
Just remember:
Just remember:
•• each gamete must have ONE COPY OF EACH
each gamete must have ONE COPY OF EACH
GENE
GENE
•• random segregation and independent
random segregation and independent
assortment still apply
assortment still apply

4. Trihybrid crosses
Trihybrid crosses
•• The basic concepts are the same as with mono- or
The basic concepts are the same as with mono- or
dihybrid crosses
dihybrid crosses
•• Just remember:
Just remember:
•• each gamete must have ONE COPY OF EACH
each gamete must have ONE COPY OF EACH
GENE
GENE
•• random segregation and independent assortment
random segregation and independent assortment
still apply
still apply

5. Trihybrid crosses
Trihybrid crosses
•• tall, pinched pod, axial X dwarf, inflated, terminal
tall, pinched pod, axial X dwarf, inflated, terminal
•• TT pp AA
TT pp AA tt PP aa
tt PP aa
•• F11::
F tall, inflated, axial
tall, inflated, axial
Tt Pp Aa
•• F1 X F1 --> ?

6. Trihybrid crosses
Trihybrid crosses
•• Step one: Figure out the gametes
Step one: Figure out the gametes
produced by each parent (use 2nn))
produced by each parent (use 2
•• Parents: Tt Pp Aa; 233 = 8
Parents: Tt Pp Aa; 2 = 8
•• eight possible gametes from each parent:
eight possible gametes from each parent:
•• TPATPa
TPATPa TpA
TpA tPA
tPA
Tpa
Tpa tPa
tPa tpA
tpA tpa
tpa

7. Forked-line Method
Forked-line Method
•• Breaks down multi-hybrid crosses into a series
Breaks down multi-hybrid crosses into a series
of monohybrid crosses
of monohybrid crosses
•• Combine the individual ratios (multiply) to get
Combine the individual ratios (multiply) to get
the final ratio
the final ratio

8. Forked-line Method
Forked-line Method
Tt Pp Aa X Tt Pp Aa
Tt Pp Aa X Tt Pp Aa
Break into Tt X Tt; Pp X Pp; Aa X Aa
Break into Tt X Tt; Pp X Pp; Aa X Aa
•• Tt X
Tt X Tt --> 3/4 T: 1/4 tt
Tt --> 3/4 T: 1/4
•• Pp X
Pp X Pp --> 3/4 P: 1/4 p
Pp --> 3/4 P: 1/4 p
•• Aa X
Aa X Aa --> 3/4 A: 1/4 a
Aa --> 3/4 A: 1/4 a

9. Forked line
Forked line
FF offspring:
2 offspring: 3/4 A --> 27/64 TPA
2
3/4 P
< 1/4 a --> 9 /64 TPa
3/4 T
< 1/4 p
3/4 A
1/4 a
--> 9 /64 TpA
--> 3 /64 Tpa
3/4 A --> 9 /64 tPA
3/4 P
< 1/4 a --> 3 /64 tPa
1/4 t
< 3/4 A --> 3 /64 tpA
1/4 p
< 1/4 a --> 1 /64 tpa

10. Forked-line
Forked-line
•• Can find genotypic ratios
Can find genotypic ratios
•• substitute 1/4 TT; 1/2 Tt; 1/4 tt, etc.
substitute 1/4 TT; 1/2 Tt; 1/4 tt, etc.
•• Can go straight to one phenotype or genotype
Can go straight to one phenotype or genotype
•• ignore all branches except those leading to the desired
ignore all branches except those leading to the desired
phenotype or genotype
phenotype or genotype

11. Trihybrid
Trihybrid
Cross
Cross

12. The Principle of Independent
The Principle of Independent
Assortment
Assortment
•• Factors for different
Factors for different
traits assort
traits assort
independently of one
independently of one
another
another
•• Genes are inherited
Genes are inherited
independently of each
independently of each
other
other
•• Segregate randomly in
Segregate randomly in
gametes
gametes
•• Dihybrid Cross
Dihybrid Cross

14. Branch Diagram of Dihybrid Cross
Branch Diagram of Dihybrid Cross
P
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e
n
o
t
y
p
e

15. Genotype vs.
Genotype vs.
Phenotype
Phenotype