All four B2 hybrid crosses

Sex-Linked Traits   XX-XY system

Trait is completely dominant

 

 

There are four possible B2 crosses.  The progeny distributions depend on the genotypes of the mother and fathers of the cross (i.e, P1, F1 or F1').  The expected genotypic distributions of the four crosses are diagramed below. 

 

Reminder :

The P2 generation has genotypes A2A2 & A2Y2;   The P1 generation has genotypes A1A1 & A1Y1.  The F1 has genotypes A1A2 & A1Y2 and the F1' generation has genotypes A1A2 & A2Y1

 


 

B2 Hybrid Cross    Phenotype

           (P2 x F1) = A2A2 x A1Y2

Progeny

    

A1A2

 ♀

100% P1 phenotype

A2Y2

 ♂

100% P2 phenotype

B2' Hybrid Cross

  

 Phenotype

       (F1 x P2) = A1A2 x A2Y2
  

 

 

1/2 A1A2 ; 1/2 A2A2

 ♀

1/2 P1; 1/2 P2 phenotypes

1/2 A1Y2 ; 1/2 A2Y2

 ♂  1/2 P1; 1/2 P2 phenotypes

 

B2'’ Hybrid Cross

    

       (P2 x F1') = A2A2 x A2Y1
 

 

  

A2A2

 ♀

100% P2 phenotype

A2Y1

 ♂

100% P2 phenotype

 

B2'" Hybrid Cross

   
            (F1'x P2) = A1A2 x A1Y1
 

 

  

1/2 A1A1 ; 1/2 A1A2

 ♀ 1/2 P1; 1/2 P2 phenotypes

1/2 A1Y1 ; 1/2 A2Y1

 ♂  1/2 P1; 1/2 P2 phenotypes

 

 

With complete dominance (if the Y chromosome has no effect) of the A1 allele, there are still three different inheritance patterns. For the B2'and B2'" Crosses the males and females show the same patterns.  That is, 1/2 the progeny have a P1 phenotype and 1/2 the progeny have a P2 phenotype. In the B2 cross, all of the females have the P1 phenotype and all of the males have the P2 phenotype.  In the B2'’ all of the males and all of the females have the P2 phenotype.

 

If the heterozygote has a unique phenotype, the results are somewhat different (see number 4 below).

B2 crosses
1 Definition
2 Single Autosomal Traits - All dominance patterns
4 Single Sex-linked Trait (XY)  - Complete Dominance dominance
4 Single Sex-linked Trait (XY)  - Other dominance patterns
5 Single Sex-linked Trait (ZW)  - All dominance patterns (inactive)
5 Two autosomal traits - unlinked genes -All dominance patterns (inactive)
6 Two autosomal traits -linked genes - All dominance patterns (inactive)
7 Some general rules for two or more genes (inactive)
8 Problems (inactive)
  Also See  - Test Crosses
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