Abstract: The invention provides methods of monitoring expression of a plurality of genes in a cell or small population of cells. Preferred methods entail contacting an array of probes with a population of nucleic acids derived from a population of fewer than 1000 cells then determining the relative hybridization of the probes to the population of nucleic acid as a measure of the relative representation of genes from the cells. The invention further provides methods of classifying cells. These preferred methods entail determining an expression profile of each of a plurality of cells then classifying the cells in clusters determined by similarity of expression profile. The invention further provides methods of monitoring differentiation of a cell lineage. These preferred methods entail determining an expression profile of each of a plurality of cells at different differentiation stages within the lineage. These cells can then be classified into clusters determined by similarity of expression profile.

Abstract: This invention provides an isolated nucleic acid molecule encoding a vertebrate pheromone receptor. This invention also provides a nucleic acid molecule of at least 12 nucleotides capable of specifically hybridizing with a unique sequence within the sequence of the nucleic acid molecule which encodes a pheromone receptor. This invention provides a vector which comprises the above-described isolated nucleic acid molecule. This invention also provides a purified, vertebrate pheromone receptor. This invention provides an antibody capable of specifically binding to a vertebrate pheromone receptor. The invention further methods for identifying ligands capable of affecting the activity of a pheromone receptor. This invention provides different uses of the identified ligands. This invention also provides a transgenic nonhuman living organism expressing a pheromone receptor.