Tutor profile: Darren L.

What is the basic layout of an R function?

name.of.function <- function(arg1, arg2) { statements return(something) }

Why is the boiling point higher for water than hydrogen sulfide?

Unlike hydrogen sulfide, water molecules are able to hydrogen bond to each other. Water is a dipolar molecule—the polarity of the O-H bond allows the partial positive hydrogen to hydrogen bond with the partial negative oxygen of a neighboring water molecule. Water's tetrahedral shape allows each water to hydrogen bond with up to four other water molecules. Hydrogen sulfide molecules cannot form hydrogen bonds with one another due to the larger size of the sulfur atom. As such, water's increased cohesion (due to its ability to hydrogen bond) makes it more difficult to free water molecules from their liquid state, leading to its higher boiling point.

Mendel used pea strains for which purple flower color (P) was dominant to white flower color (p), round peas (R) were dominant to wrinkled peas (r), and yellow peas (Y) were dominant to green peas (y). Imagine Mendel crossed a true-breeding strain of peas with white flowers and round, green seeds to another true-breeding strain with purple flowers and wrinkled, yellow seeds. Among the first generation (F1) trihybrids, what color(s) would the flowers be and what would be the colors and shapes of the peas?

Given that both strains Mendel crossbred were true-breeding, we know that we are looking at a trihybrid cross as follows: ppRRyy X PPrrYY. The offspring must then be PpRrYy, as each receives one allele each from both parents. We can then deduce that all first generation offspring have purple flowers and round, yellow peas.