You measure the recombination frequency between two genes using a testcross between a double heterozygote and a double recessive homozygote, as is standard practice. you obtain four progeny classes, as expected, and from them you calculate a recombination frequency of 70%. you realize that you must have misidentified the parental and recombinant progeny. why?

Explanation:

When analyzing two linked genes there are 2 possibilities: either there is recombination between them during meiosis or there is no recombination. Crossing over happens during meiosis I, when each chromosome has two sister chromatids.

If no recombination happens, the 4 resulting gametes will be parental.

If recombination happens, 2 gametes will be parental and 2 gametes will be recombinant. For that reason, the maximum recombination frequency between two genes that can be calculated is 50% (recombination frequency = recombinants/total).

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.