Which of the following statements would explain a testcross involving f1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced? a. recombination did not occur in the cell during meiosis. b. both of the characters are controlled by more than one gene. c. the two genes are linked but on different chromosomes. d. the two genes are closely linked on the same chromosome.

d. The two genes are closely linked on the same chromosome.

Explanation:

In a testcross involving F1 dihybrid, parent with both the recessive traits is crossed with the F1 dihybrid. Offspring is expected in 1:1:1:1 ratio because formation of gametes is a random process and parental type and recombinant type gametes are expected to be produced in same numbers.

If the two genes are present near to each other on same chromosome they can exhibit linkage. They show tendency to get inherited together. Hence new recombinants are produced in lesser number than the parental type offspring.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c