: 11 The later definition by Cavalli-Sforza & Bodmer (1971) is currently used: Genetic polymorphism is the occurrence in the same population of two or more alleles at one locus, each with appreciable frequency, where the minimum frequency is typically taken as 1%.
The financial world splits up its calendar into four quarters, each three months long. If January to March is the first quarter, April to June is the second quarter, and so on, though a company's first quarter does not have to begin in January.
A quarter of a year, one fourth, is three months, as in financial quarters. I don't know if there is a term for 4 months. 12 weeks in a trimester, 3 months in a trimester, 4 weeks in a month. since there is 3 trimesters and there is 40 weeks in a normal pregnancy that means approximately 13 weeks per trimester.