Zygote
A diploid cell formed by fusion of two gametes.
A zygote is a eukaryotic cell formed by a fertilization event between two gametes. Its genome is a combination of the DNA in each gamete and contains all of the genetic information of a new individual organism. The sexual fusion of haploid cells is called karyogamy, resulting in a diploid cell known as the zygote (or zygospore in specific cases).
- field
- Cell biology, developmental biology
- known_for
- Earliest developmental stage in multicellular organisms; formed by fusion of egg and sperm cells
Lore & Background
He observed that only one sperm entered the ovum and that sometime after, the two pronuclei fused into one nucleus. From these observations, Hertwig concluded that an essential part of fertilization was the fusion of the two pronuclei to form the nucleus.
Reader's Guide
The zygote represents the earliest developmental stage in multicellular organisms. In humans and most other anisogamous organisms, a zygote is formed when an egg cell and sperm cell come together to create a new unique organism. The formation of a totipotent zygote with the potential to produce a whole organism depends on epigenetic reprogramming, including DNA demethylation of the paternal genome. In human fertilization, a released ovum and a haploid sperm cell combine to form a single diploid cell. After approximately 30 hours, fusion of the pronuclei and immediate mitotic division produce two diploid daughter cells called blastomeres. The developing embryo is sometimes termed a preimplantation embryo between fertilization and implantation. The human zygote has been genetically edited in experiments designed to cure inherited diseases. In fungi, the zygote may enter meiosis or mitosis depending on the life cycle. In plants, the zygote may be polyploid if fertilization occurs between meiotically unreduced gametes, and in land plants it forms within the archegonium. In single-celled organisms, the zygote can divide asexually by mitosis.
Did You Know?
- The term 'zygote' comes from Ancient Greek ζυγωτός (zygōtós) meaning 'joined, yoked'.
- German zoologist Oscar Hertwig first proved that only one sperm enters the ovum and that the two pronuclei fuse into one nucleus.
- In humans, after approximately 30 hours from fertilization, fusion of the pronuclei and mitotic division produce two diploid daughter cells called blastomeres.
- The human zygote has been genetically edited in experiments designed to cure inherited diseases.
Frequently Asked Questions
What is a Zygote?
A zygote is the single diploid cell that marks the very first stage of a new multicellular organism, created when two gametes unite. It is the earliest recognizable developmental stage in organisms that reproduce sexually.
How is a Zygote formed?
It comes into existence through fertilization, where a sperm cell and an egg cell each contribute their haploid set of chromosomes. The specific nuclear-fusion step that merges those two sets is called karyogamy.
Why is the Zygote important?
It carries the complete combined genetic blueprint for the entire new individual, making it the starting point from which all subsequent cell division and differentiation unfold.
What is the ploidy of a Zygote?
A zygote is diploid, meaning it holds two full sets of chromosomes—one inherited from each parent gamete.
Which fields of biology focus on the Zygote?
It sits at the intersection of cell biology and developmental biology, as it represents the earliest recognizable stage in the life cycle of multicellular organisms.
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