In certain plants, tall is dominant to short. A member of your class accidentally did not record the genotype of the parent plants prior to mating them. Following the cross, you notice that the phenotypic ratio for tall to short plants is 1:1. Identify the cross that could have produced these results. Justify your reasoning

Heterozygous tall (Tt) and homozygous short (tt) parents

Explanation:

This question involves a single gene coding for height in a certain plant. The allele for tallness (T) is dominant over the allele for shortness (t). This means that allele 'T' will always mask the phenotypic expression of allele 't' in a heterozygous state.

According to the question, the genotypes of the parent plants that were crossed were not recorded but tall and short offsprings in a ratio 1:1 were observed. Based on this phenotypic ratio, one of the parents has to be heterozygous for the trait and the other homozygous for the recessive trait in order to produce offsprings with equal ratio of tall and short traits.

This means that the heterozygous tall parent will have a genotype: Tt, and be phenotypically tall since Tallness is dominant to shortness. The other parent which is homozygous recessive will have a genotype: tt.

In a nutshell, a cross between parents with genotypes; Tt and tt will produce four possible offsprings with two distinct genotypes i.e. Tt and tt.

Tt offsprings (2) will be phenotypically tall

tt offsprings (2) will be phenotypically short

Hence, the phenotypic ratio will be 2:2 equivalent to 1:1

"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."