Summary
The single cell formed at fertilisation that divides to become an embryo.
In depth
The zygote contains maternal cytoplasmic determinants and paternal and maternal genomes. Early development is driven by maternal mRNA until zygotic genome activation (about the 4 to 8 cell stage in humans).
The zygote begins DNA replication within hours and its first division takes about 24 hours in humans. Maternal factors in the egg cytoplasm control the first divisions.
Key idea: a single cell contains all the information, plus the machinery, to build an organism.
The zygote is the single diploid cell created by fertilisation, with a genome from each parent plus the mother's cytoplasm and mitochondria. It is totipotent and can form every cell of the embryo and its supporting tissues.
In many animals the zygote's cytoplasm holds maternal mRNAs and proteins that direct the first divisions before the embryo's own genes switch on (zygotic genome activation, around the 2 to 4-cell stage in humans). Egg yolk content affects cleavage patterns.
Example: in frogs, the grey crescent appears opposite the sperm entry and marks the future dorsal side.
Remember: all the cells of an adult descend from this one cell.
Frequently asked questions
What is Zygote?
The single cell formed at fertilisation that divides to become an embryo.
Which area of biology covers Zygote, and how advanced is it?
Zygote is one of the 54 topics in Developmental Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Cleavage, Embryo, Maternal Effect Genes.
Can you give an example of Zygote?
A zygote is totipotent.
What should I learn before Zygote?
Zygote is a Beginner topic, so no earlier topic is required. Other Beginner topics in Developmental Biology that pair well with it include Fertilisation, Embryo, Cleavage.
What topics are related to Zygote?
The closest topics to Zygote are Cleavage, Embryo, Maternal Effect Genes, Totipotency. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Zygote?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Zygote. To practise the whole of Developmental Biology, use the Developmental Biology quiz.
How is Zygote different from Cleavage?
Zygote: The single cell formed at fertilisation that divides to become an embryo. Cleavage: Rapid cell divisions of the early embryo without growth, producing a ball of smaller cells. Read both side by side and note what each one explains.
How should I study Zygote step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Cleavage and explain the difference aloud. Finally, take the Developmental Biology quiz and come back to this page for any question you miss.