Which term refers to embryos at the 2-cell stage up to just before the morula stage?

Which term refers to embryos at the 2-cell stage up to just before the morula stage?

• A. Birth (single)
• B. Blastocoele
• C. Cleavage stage embryos
• D. Chimerism

Answer: (C)

The key idea is the sequence of early embryo divisions called cleavage. After fertilization, the zygote divides without increasing in overall size, creating more and more cells: 2-cell, then 4-cell, then 8-cell, and so on, all during the cleavage phase. This phase continues up to, but not including, the morula stage, which is when the embryo becomes a solid ball of cells. So embryos at the 2-cell stage up to just before the morula are described as cleavage stage embryos. Other options don’t fit: the blastocoele is the cavity that forms inside a blastocyst after the morula, chimerism refers to a mixed genetic origin, and “birth (single)” is not a developmental term.

The key idea is the sequence of early embryo divisions called cleavage. After fertilization, the zygote divides without increasing in overall size, creating more and more cells: 2-cell, then 4-cell, then 8-cell, and so on, all during the cleavage phase. This phase continues up to, but not including, the morula stage, which is when the embryo becomes a solid ball of cells. So embryos at the 2-cell stage up to just before the morula are described as cleavage stage embryos.

Other options don’t fit: the blastocoele is the cavity that forms inside a blastocyst after the morula, chimerism refers to a mixed genetic origin, and “birth (single)” is not a developmental term.