ZOO501 Midterm Merged PPT Handouts by Aarish Ali

All multicellular organisms arise by a slow process of progressive change called development. Development is a process by which a multicellular organism arises, initially from a single cellthe fertilized egg, or zygote, which divides mitotically to produce all the cells of the body. The study of animal development has traditionally been called embryology, from that stage of an organism that exists between fertilization and birth. Each day we replace more than a gram of skin cells (the older cells being sloughed off as we move), and our bone marrow sustains the development of millions of new red blood cells every minute of our lives.