Embryo vs Zygote
Every living being starts from a zygote and goes through the embryo stage before becoming adults. Humans and most of the mammals pass these stages mostly unknown in the very early stages of their lives. There are many differences between the embryo and zygote in the size, number of cells, and many others, but most of the people are not aware of those; instead, both stages are understood as similar. This article intends to explore the difference between those important stages of life.
When a gamete derived from the paternal gene pool arrives at the gamete derived from the maternal gene pool, the fertilisation takes place to form the zygote. That means zygote is the first stage of an organism, which is a unicellular stage formed as a result of the fusion of genetic material from both parents in sexual reproduction. The gametes are haploid, but when the maternal and paternal gametes are fused, the formed zygote becomes diploid.
In mammals, the zygote formation is followed by its movement through the fallopian tube into the endometrium, the uterus wall. The zygote starts to divide mitotically while traveling through the fallopian tube and implants itself in the endometrium of the womb. The division of the zygote takes place through the process called cleavage. In is interesting to notice that the size of the zygote does not change while it is going through the cleavage, but the number of cells go high.
The lifetime of a human zygote is about four days, after that it reaches the stage of blastula, which becomes the gastrula through gastrulation, and then becomes the embryo.
Embryo is one of the early stages of the lifecycle of eukaryotic animals. According to definitions for embryo, it has been described as an eukaryotic multicellular organism at its earliest stage. The formation of the embryo is called the embryogenesis, which takes place after the zygote is formed. However, embryo means something that grows in Greek language.
The embryo starts to increase its size with time, but the embryogenesis does not change the size although it increases the number of cells through mitosis. That means the cleavage does not change the original size of the ovum but after the formation of embryo it starts to swell. It would be important to know that the embryo stage starts when the zygote is implanted in the uterus wall, in humans. The embryo stage starts in humans after the formation of gastrula following blastula from zygote. After that, the embryo stage remains until eight weeks from fertilization or ten weeks from last menstrual period. The organogenesis or the formation of organs takes place in this stage with neurogenesis, angiogenesis, chondrogenesis, ostiogenesis, myogenesis, and other tissues. When all the basic germ cell layers are formed, the stage of embryo will be advanced into foetus. However, it is not termed as the foetus in birds and other egg-laying animals but as the embryo regardless of its developmental stage. That means the egg-laying animals have an embryonic stage and then a hatchling or larva.
What is the difference between Embryo and Zygote?
• Zygote is the most initial stage of an organism while it becomes an embryo later.
• Zygote is unicellular and becomes multicellular, while embryo starts as a multicellular stage.
• Zygote does not change its size with time, but embryo increases its size with time.
• Embryo undergoes through organogenesis but not the zygote. In other words, embryo performs specialization of cells but not the zygote.
• Zygote is moving through the fallopian tube, but embryo is always implanted in mammals.