Final answer:
Mesodermal development in a 32-cell embryo includes the formation of the mesoderm during gastrulation by the third week of development, which will give rise to structures like bones, muscles, and the heart.
Step-by-step explanation:
During the second week after fertilization, the embryoblast differentiates into two groups of cells known as the epiblast and the hypoblast, forming a bilaminar embryonic disc. By the end of the second week, a critical phase called gastrulation occurs which results in the formation of three primary germ layers: the endoderm, mesoderm, and ectoderm. These layers will develop into various types of cells and organs within the body, with the mesoderm giving rise to structures such as bones, muscles, and the heart.
The mesoderm develops from the two-layered disc during gastrulation, where cells migrate through the primitive streak to form this middle layer. The ectoderm, the outermost layer, will eventually derive the skin and nervous system, while the endoderm forms internal glands and organs. Following fertilization, the zygote divides through mitosis, creating a structure called the blastocyst, which consists of an inner cell mass and trophoblast with a fluid-filled cavity. This blastocyst then implants into the uterine wall.
Differentiation of cells begins in the third week after fertilization where cells turn from totipotency to multipotency. This pivotal stage is marked by specific gene expression patterns that allow the cells to become specialized and develop into different tissues and organs.