It is of great interest to understand the relationship between the genotype (e.g., having an altered chromosome number) and the phenotype (the appearance of the organism, including its fitness). When an organism has an extra copy of a chromosome it is trisomic. By the 1940s, the mechanisms by which trisomy occurs were understood in detail. The jimsonweed (Datura stramonium L.), a flowering plant of the potato family (Solanaceae), normally has 12 pairs of chromosomes. Albert Blakeslee (1874–1954) investigated the seed capsule from wild-type Datura (top) and 12 distinct trisomic types. For each trisomic type, a diagram of the extra chromosome is shown, including a numbering system for the chromosome ends (telomeres). Blakeslee noted that since each chromosome has a distinctive set of genes, each trisomic plant has a distinctive phenotype. From Riley (1948, p. 420). Used with permission.
Nil adeo quoniam natum'st in corpore, ut uti possemus, sed quod natum'st, id procreat usum. (In fact, nothing in our bodies was born in order that we might be able to use it, but rather, having been born, it begets a use.)
—Lucretius (c.100–c.55 B.C.E.), De Rerum Natura, IV, 834–835 (1772, p. 160).
INTRODUCTION TO FUNCTIONAL GENOMICS
A genome is the collection of DNA that comprises ...