Definition

Noun: A blastomere is any of the cells formed by the early, rapid divisions (cleavage) of a fertilized egg (zygote) during the initial stages of embryonic development.

Usage

The term is used specifically in the fields of embryology and developmental biology to describe the individual cells that make up the early embryo (morula) before it forms a blastocyst. * In the first few hours after fertilization, the zygote undergoes cleavage, dividing into two, then four, then eight blastomeres. * The size and potency of blastomeres can vary between different animal species.

Examples

• The 8-cell embryo is composed of eight distinct blastomeres.
• Researchers observed the blastomere under a microscope to study its structure.
• In some organisms, each blastomere at the 4-cell stage is still totipotent, meaning it has the potential to develop into a complete organism.

Advanced Usage

• Blastomere Biopsy: A technique used in preimplantation genetic diagnosis (PGD), where one or two blastomeres are removed from an early embryo for genetic testing without significantly harming the embryo's development.
• Blastomere Asymmetry: Refers to differences in size, cytoplasmic content, or developmental fate between blastomeres in the early embryo, which is a crucial step in cell differentiation.

Variants and Related Words

• Blastomeric (adjective): Of or relating to blastomeres.
  • The blastomeric divisions were synchronous.
• Meroblast (noun): A type of incomplete cleavage where only part of the egg divides, relevant to the study of blastomere formation in certain eggs (like those of birds or fish).
• Holoblast (noun): A type of complete cleavage where the entire egg divides, as seen in mammals and many other species, producing typical blastomeres.

Synonyms

• Cleavage cell
• Embryonic blast cell (in the very early context)

Notes on Meaning

The term blastomere refers exclusively to the cells produced during the cleavage stages, prior to the formation of the blastocyst. Once the embryo organizes into a hollow ball of cells (the blastocyst), the cells are typically referred to by more specific terms like trophoblast cells (outer layer) and inner cell mass cells.

Noun

1. any cell resulting from cleavage of a fertilized egg