Fruit color in a particular plant is controlled by a set of three quantitative trait loci (i. e., qtls or polygenes), that work in an equal and additive manner. each qtl has two alleles (i. e., a and a); each allele represented by a capital letter produces one dose of yellow pigment, while alleles represented with lower case letters do not produce any pigment at all. a trihybrid plant (a/a; b/b; c/c) is selfed. assuming no effects of the environment, what proportion of the offspring will have the same fruit color phenotype as the trihybrid parent?

1/8

Explanation:

Given that the trihybrid parents have AaBbCc genotype for fruit color. The trait is a quantitative trait i.e. each dominant allele will have an additive effect on it. In this case, AaBbCc and AABBCC will not produce same fruit color because AaBbCc has only three loci contributing to the color while in AABBCC all the six loci are contributing to the color. For an offspring to be exactly similar to the AaBbCc parents it should have the same genotype of AaBbCc.

The probability of Aa to come from a cross between Aa and Aa is 2/4 or 1/2

The probability of Bb to come from a cross between Bb and Bb is 2/4 or 1/2

The probability of Cc to come from a cross between Cc and Cc is 2/4 or 1/2

So the collective probability of AaBbCc offspring from a cross between AaBbCc and AaBbCc parents would be=

1/2 * 1/2 * 1/2 = 1/8

Hence, assuming no effects of the environment, 1/8 of the offspring will have the same fruit color phenotype as the trihybrid parent.

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."