Information Available from the B2 progeny - Autosomal Inheritance


        The B2 backcross is a cross of an F1 or F1' individual to a P2  individual.  The F1 or F1' individual may be the male or the female.  These, two crosses will give the same progeny genotypes. The expected B2 genotypes for a single autosomal gene are given below.

B2 Backcross - Autosomal Traits

For a single autosomal gene, the B2 backcrosses give the same genotypes for both males and females.  One half of the genotypes will be homozygous (the same genotype as the P2 parent) and 1/2 of the genotypes will be heterozygous (the same genotype as the  F1 or F1' parent).

The P2 parent has Genotype A2A2.  If the A2 allele is completely recessive, half of the progeny will look like the P1 parent and half of the progeny will look like the P2 parent.  The expected results for other dominance patterns are given below.

 

Dominance of Mutant Allele

 Autosomal
A2 Allele is Recessive

 

 1/2 of the B2 progeny (male and female) have the P1 phenotype and 1/2 of the progeny (male and female) have the P2 phenotype
A2 Allele is Incompletely Dominant

 

 1/2 of the progeny (male and female) have the P2 phenotype and 1/2 the progeny (male and female) have a phenotype that is intermediate to the  P1 and P2 parental phenotypes.
A2 Allele is Overdominant 1/2 of the progeny (male and female) have the P2 phenotype and 1/2 the progeny (male and female) have a phenotype that is more extreme than  the  P1 and P2 phenotypes.
 
A2 Allele is Codominant with A1 allele  1/2 of the progeny (male and female) have the P2 phenotype and 1/2 the progeny (male and female) show both  the P1 and P2 parental phenotypes, simultaneously.
 

 

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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