Final answer:
Observing more parental-type offspring than recombinant-type offspring in the progeny of a test cross indicates that the genes are linked and located on the same chromosome, with a certain distance between them that allows for recombination. Recombination occurs in a significant minority of offspring, suggesting crossover events during meiosis.
Step-by-step explanation:
When a test cross involving F₁ dihybrid flies produces more parental-type offspring than recombinant-type offspring, it indicates that the genes are on the same chromosome, but with some separation that allows for occasional recombination. Parental types are those progeny that have inherited the same genetic alleles as their parents. Recombinant types, also known as nonparental types, result from homologous recombination during meiosis, exhibiting a different allelic combination compared to their parents.
Morgan's experiments on fruit flies revealed that genes could either be linked or unlinked. Linked genes tend to be inherited together and result in a higher proportion of parental types during a test cross, while unlinked genes follow Mendelian independent assortment and produce equal proportions of parental and nonparental types. A significant deviation from a 1:1:1:1 ratio of the four possible gametes in a dihybrid cross suggests gene linkage with varying degrees of crossing over depending on the distance between the genes on the chromosome.
Therefore, when you observe 17% recombinant progeny, it implies that the genes are linked, and that crossover events between these genes happen sometimes, but not as frequently as they would if the genes were on different chromosomes or far apart on the same chromosome.