A blastula is the next step of development after a zygote.  It is formed in the cleavage process as blastomeres arrange into a sphere.  

Blastula

A zygote is formed through the process of fertilization.  It is a single cell that goes on to mitotically divide in order to produce all of the cells of an organism's body.  

Michigan State University

Fertilization is the fusion of a sperm and an egg, a process that initiates genetic variation. In humans, both the sperm and the egg contribute 23 chromosomes each. Their combination results in the formation of a zygote, a single cell containing a complete set of 46 chromosomes, organized into 23 pairs.

Fertilization

Barresi, M. J., &amp; Gilbert, S. F. (2020). Developmental Biology (12th ed.). New York: Sinauer.

Developmental Biology (12th ed.)

Zygote

A zygote is the single cell created when a sperm and an egg fuse. Because the egg and the sperm each carry 23 chromosomes, their fusion results in a zygote with a total of 46 chromosomes, arranged in 23 pairs. Through this process, each parent contributes half of the offspring's genetic information.

This microscopic image captures the moment of fertilization, showing a single sperm cell penetrating and fusing with an ovum (egg cell).

Microscopic View of Fertilization

A new single-celled organism is formed when a sperm and an egg fuse, with each contributing a set of chromosomes. If an error occurs causing one of the contributing cells to have an extra chromosome, what is the most direct consequence for the newly formed organism?

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