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Expected Phenotypes of F2 Cross - Single Autosomal Traits All Dominance patterns |
1. Complete dominance - A (Red) > (a) Green
As previously stated the genotypic array in an F2 Cross is 1/4A1A1:1/2A1A2:1/4A2A2. Since red is completely dominant to green any genotype with either one or two A1 (Red alleles) will have the red phenotype. Therefore, the expected phenotypic ratios among the F2 progeny are:
3/4 Red ( 1/4A1A1 + 1/2A1A2)
1/4 Green (1/4A2A2)
2. Incomplete Dominance A1A1 (Tall) > A1A2 (medium) > A2A2 (short)
The genotypic ratio in an F2 Cross is 1/4A1A1:1/2A1A2:1/4A2A2. Each genotype for an incompletely dominant trait has its own phenotype. Therefore, the expected phenotypic ratios among the F2 progeny are:
| 1/4 Tall (A1A1) | |
| 1/2 Medium (A1A2) | |
| 1/4 Short (A2A2) |
3. Overdominance: A1A1 (Pink) > A1A2 (Blood Red) > A2A2 (Light Red)
The genotypic ratio in an F2 Cross is 1/4A1A1:1/2A1A2:1/4A2A2. Each genotype for an incompletely dominant trait has its own phenotype. However the heterozygote is more extreme than either of the parents. The phenotypic ratios for overdominant traits are the same as for incompletely dominant traits. Therefore, the expected phenotypic ratios among the F2 progeny are:
| 1/4 Pink (A1A1) | |
| 1/2 Blood Red (A1A2) | |
| 1/4 Light Red (A2A2) |
4. Codominance: A1A1 (A antigen) is codominant to A2A2 (B antigen). The heterozygote A1A2 has both A and B antigens
The genotypic ratio in an F2 Cross is 1/4A1A1:1/2A1A2:1/4A2A2. Each genotype for an codominant trait has its own phenotype. However the heterozygote has both parental phenotype the parents. The phenotypic ratios for overdominant traits are the same as for incompletely dominant traits. Therefore, the expected phenotypic ratios among the F2 progeny are:
1/4 A antigen(A1A1) 1/2 A and B antigen (A1A2) 1/4 B antigen (A2A2)
Quick Links F2 Cross
1 Basic F2 cross - autosomal genes 2 Basic F2 cross- X-linked gene Expected Phenotypes of F2 Cross - Single Autosomal Traits Expected Phenotypes of F2 Cross - X-linked gene 4 F2 cross - two unlinked autosomal genes 5 F2 cross - one autosomal - one X-linked gene 6 Linkage - Coupling and Repulsion 7 F2 cross - two linked autosomal genes -coupling 8 F2 cross - two linked autosomal genes - repulsion 9 Measuring the recombination rate from F2 data Recombination from F2 data - Table of Values 10 Basic F2 cross- Z-linked gene (inactive) 12 Expected Phenotypes of F2 Cross - Z-linked gene (inactive) 13 F2 cross - one autosomal - one Z-linked gene (inactive) Also See
Detection of Linkage - Basic Info - Two Autosomal Traits - Complete Dominance Detection of Linkage - More complex examples Detection of Linkage - One More Example Detection of Linkage - Two Autosomal Traits - Heterozygote has Unique Phenotype Home page Detailed List for Mendelian Genetics