The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects, and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms.

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form.

At the turn of the twentieth century, Edmund B. Wilson performed experiments to show where germinal matter was located in molluscs. At Columbia University in New York City, New York, Wilson studied what causes cells to differentiate during development. In 1904 he conducted his experiments on molluscs, and he modified the

The Cell in Development and Inheritance, by Edmund Beecher Wilson, provided a textb

Studies in Spermatogenesis is a two volume book written by Nettie Maria Stevens, and published by the Carnegie Institution of Washington in 1905 and 1906.

Walter Stanborough Sutton studied grasshoppers and connected the phenomena of meiosis, segregation, and independent assortment with the chromosomal theory of inheritance in the early twentieth century in the US. Sutton researched chromosomes, then called inheritance

Edmund Beecher Wilson contributed to cell biology, the study of cells, in the US during the end of the nineteenth and the beginning of the twentieth centuries.

Endoderm is one of the germ layers—aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. All animals, with the exception of sponges, form either two or three germ layers through a process known as gastrulation.

Edmund Beecher Wilson in the US published An Atlas of Fertilization and Karyokinesis of the Ovum (hereafter called An Atlas) in 1895. The book presents photographs by photographer