In a cross between two tall plants with yellow seeds that are heterozygous on both traits (TtYy), supposed Mendel discovered that a small number of offspring (5-6%) from these parents were short and green (ttyy). What does this say about the T and Y genes

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A test-cross can reveal an unknown genotype. As the plants are heterozygous they sort independently of each other. when they are cross linked dominant genes express themselves in most of the cases whereas the recessive genes also express themselves resulting in the formation of tall and yellow plants and as well as  short and green plants.

Explanation:

  The impact of a single gene on more than one characteristic is called pleiotropy.  Mendel deduced from his results that each individual had two discrete copies of the characteristic that are passed individually to offspring.Mendel called the dominant allele the expressed unit factor; the recessive allele was referred to as the latent unit factor.Mendel’s law of dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. The recessive trait will only be expressed by offspring that have two copies of this allele and these offspring will breed true when self-crossed.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.