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Genetic trihybrid cross
A trihybrid cross involves three traits and uses a Punnett square with 64 boxes to demonstrate that Mendel's principles of segregation and independent assortment apply to the inheritance of multiple traits. The document discusses using forked-line and branch diagram methods to break down a trihybrid cross into a series of monohybrid crosses in order to calculate genotypic and phenotypic ratios.
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Genetic trihybrid cross
- 1. Trihybrid cross Trihybrid cross Morecomplex 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 PUNNETTSQUARE 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 FFoffspring: 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.
- 12. The Principle ofIndependent 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 ofDihybrid Cross Branch Diagram of Dihybrid Cross P h e n o t y p e
- 15.