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Multi-generational plant breeding

Each plant was crossed with normal (leafy) pure-bred plants to generate the following phenotypic ratios:

F1 phenotype F2 phenotype

Line 1 x leafy all leaves 3:1 leaves/no leaves

Line 2 x leafy all no leaves 3:1 no leaves/leaves

Line 1 X line 2 all no leaves 13:3 no leaves/leaves

Why do two apparently similar plant lines produce such different results? For each cross depicted in the table, show the genotypes of all parental, F1, and F2 plants. Show the results of a total of three crosses.

I cannot put togeter Line 1 x Line 2...single lines don't give me problems (I think)but I cannot figure out crossing them togeter. Help

Solution Preview

Whenever you see a 13:3 ratio you should immediately think of dominant suppression epistasis. That is certain genes have the ability to suppress the expression of a gene at a second locus. Let us say, as in your question, that synthesis of a leaf is controlled by the A gene and the suppression of synthesis is controlled by the B gene. Both A and B are dominant traits. The F1 plant with the genotype AaBb will not produce leaves because of the presence of the dominant B allele.

Genotype ...

Solution Summary

This question is a typical Mendelian genetics problem. There are two pure-breeding plant lines that generate a 3:1 and a 13:3 ratio of offspring.

The solution answers the question and explains the methodology used to generate the answer. The solution is also provided in *.doc format for easier editting.