Gregor Mendel concluded from his experiments that "hereditary units" transmitted traits from one generation to the next, but at the time of his work (1850-1860's) chromosomes had not yet been observed. Around the turn of the century, two events firmly placed Mendel's name in history. First, three botanists independently rediscovered Mendel's research after conducting studies similar to his. Second, scientists began to notice differences between the behavior of chromosomes (only recently observed) during mitosis and meiosis. For example, they saw that organisms had pairs of homologous chromosomes that separated during meiosis, and that the fusion of two gametes resulted in a zygote with the normal diploid number of chromosomes.
These facts meshed well with Mendel's Laws of Segregation and Independent Assortment, demonstrating that chromosomes contained the "hereditary units" proposed by Mendel. Mendel's work and the discovery of chromosomes and their behavior laid the groundwork for studies which revealed that genes are found in specific locations on chromosomes, and that homologous chromosomes segregate and non-homologous chromosomes independently assort during meiosis. This tutorial will more closely examine the role that chromosomes play in allele segregation. You will learn that genes (and their alleles) on different chromosomes segregate (or assort) independently. If they are on the same chromosome, however, they may or may not exhibit independent segregation.
The Learning Objectives for this tutorial are, that by the end of this tutorial you should be able to: