blastomere

Imagine the beginning of development: a fertilized egg starts dividing again and again. Each cell made during these early divisions is a blastomere. Think of these as tiny, unspecialized building blocks that eventually contribute to the tissues and organs of the growing embryo. You’ll encounter this term most often in developmental biology, where scientists study how one new life takes shape from a single starting cell.

If you look at an early embryo under a microscope, you’ll see clusters of these fast-dividing cells. At this stage they are not yet specialized and still retain broad developmental potential. A sea urchin embryo is often used in labs for blastomere studies because the cells are relatively large and easy to observe.

A blastomere is one of the cells formed during the early cleavage stages of embryonic development—a cell created when a fertilized egg divides into smaller cells. The word comes from the Greek "blastos," meaning sprout or bud, and "meros," meaning part. So, in a literal sense, it refers to a small developmental part.

These cells are not just any cells; in the earliest stages many are totipotent, and later many become pluripotent, meaning they can give rise to a wide range of cell types in the developing organism. As the embryo cleaves, the number of blastomeres increases rapidly, and they eventually form a compact ball of cells called a morula. Blastomeres then begin to arrange and differentiate, eventually contributing to all major tissues and organs.

You’ll usually see "blastomere" in embryology, developmental biology, and reproductive science. Researchers study blastomeres to understand normal embryo formation, identify developmental errors that can lead to abnormalities, and improve techniques in cloning, assisted reproduction, and stem-cell-related work.

For example, scientists may isolate a single blastomere from an early embryo and track how its fate changes as the embryo develops. They may also modify environmental conditions around blastomeres to test how signals affect their growth. Understanding these early cells helps explain the mechanics of development from a single cell to a complex organism.