Development is a process that begins with fertilization and ends with the mature organism. This process involves a complex interplay of genetic and environmental influences. The study of development seeks to understand how an organism changes over time, how it acquires the characteristics that define its adult form, and how those characteristics are expressed in different environments.
The field of developmental biology has roots in many other disciplines, including embryology, genetics, biochemistry, cell biology, ecology, and evolution. Developmental biologists use a variety of techniques to study development, including DNA sequencing and analysis, microscopy, computer modeling, and behavioral observations.
Fertilization is the union of an egg and a sperm to form a single cell called a zygote. The zygote contains all of the genetic information necessary to develop into an adult organism. This information is encoded in the genes located on chromosomes within the cells of the zygote.
During early development, the zygote divides into smaller cells called embryos. These embryonic cells begin to differentiate into the various cell types that will make up the mature organism. This process is controlled by gene expression—the activation or silencing of specific genes in response to environmental cues. As development progresses, more specialized cells and tissues arise from these earlier embryonic cell types through a process called differentiation. Differentiation enables an embryo to develop into an organism with distinct body parts that perform specific functions. For example, some cells differentiate into muscle tissue while others become part of the brain or other nervous system tissue.
Differentiation is largely driven by changes in gene expression; as certain genes are turned on or off in response to signals from neighboring cells or molecules secreted by those cells (called morphogens), they cause changes in cellular structure and function that lead to further specialization down the road