Mendelian Inheritance
Review (1 page)
Concept 5: Trait Analysis Orange Eyes
Concept 7: Trait Analysis Orange Eyes and White Skin
Practice (2 pages)
Practice (2 pages)
Concept 9: Trait Analysis Vertical Eyes and Tooth
Practice (1 page)
Concept 5: Trait Analysis: Orange Eyes 4
|
|
 |
Interpreting the Results
 F2 Analysis
How are orange eyes inherited? The F2 phenotypic ratio is approximately 3 black-eyed:1 orange-eyed (or, stated another way, 3/4 black:1/4 orange). The simplest hypothesis is that there is one gene involved and that orange eyes is recessive to black eyes. If we use the symbol o for the orange allele and O for the black (normal) allele, we can follow the cross. 
The F2 genotypes are 1 OO : 2 Oo : 1 oo. Only two phenotypes are seen because O is dominant to o , so both OO and Oo genotypes have the dominant phenotype. A 3:1 phenotypic ratio is the result of crossing two heterozygotes where one allele is completely dominant to the other allele. The 3: 1 phenotypic ratio derives from a 1:2:1 genotypic ratio of homozygote for the dominant allele : heterozygote : homozygote for the recessive allele.
Conclusion Orange eyes is explained by a single gene with the orange allele being recessive to the normal black allele. This monohybrid cross illustrates Mendel's law of segregation. Now let us look at the results of an alternative cross. |
  Results of the Cross: The F2 Generation
  |
|
