Zygote
Encyclopedia
A zygote or zygocyte, is the initial cell
formed when two gamete
cells are joined by means of sexual reproduction
. In multicellular organisms, it is the earliest developmental stage of the embryo
. In single-celled organisms, the zygote divides to produce offspring, usually through meiosis
.
A zygote is always synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development
. Zygotes are usually produced by a fertilization event between two haploid
cells—an ovum
(female
gamete) and a sperm
cell (male
gamete)—which combine to form the single diploid
cell. Such zygotes contain DNA
derived from both the parents, and this provides all the genetic information necessary to form a new individual.
In land plants
, the zygote is formed within a chamber called the archegonium
. In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the sperm cell enters. As the zygote divides and grows, it does so within the archegonium.
In animal development, the term zygote is also used more loosely to refer to the group of cells formed by the first few cell divisions, although this is properly referred to as a morula
.
In mammal
ian reproduction, after fertilization has taken place the zygote travels down the fallopian tube
, while dividing to form more cells
without the zygote actually increasing in size. This cell division is mitotic
, and is known as cleavage
. All mammals go through the zygote stage of life. Mammalian zygotes eventually develop into a blastocyst
, after which they are more generally termed an embryo, and then a fetus
.
A human zygote exists for about four days, and becomes a blastocyst
on the fifth day.
(a kind of algae
) zygote that contains chloroplast
DNA (cpDNA) from both parents.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
formed when two gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
cells are joined by means of sexual reproduction
Sexual reproduction
Sexual reproduction is the creation of a new organism by combining the genetic material of two organisms. There are two main processes during sexual reproduction; they are: meiosis, involving the halving of the number of chromosomes; and fertilization, involving the fusion of two gametes and the...
. In multicellular organisms, it is the earliest developmental stage of the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. In single-celled organisms, the zygote divides to produce offspring, usually through meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
.
A zygote is always synthesized from the union of two gametes, and constitutes the first stage in a unique organism's development
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
. Zygotes are usually produced by a fertilization event between two haploid
Ploidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
cells—an ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
(female
Female
Female is the sex of an organism, or a part of an organism, which produces non-mobile ova .- Defining characteristics :The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male...
gamete) and a sperm
Sperm
The term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
cell (male
Male
Male refers to the biological sex of an organism, or part of an organism, which produces small mobile gametes, called spermatozoa. Each spermatozoon can fuse with a larger female gamete or ovum, in the process of fertilization...
gamete)—which combine to form the single diploid
Ploidy
Ploidy is the number of sets of chromosomes in a biological cell.Human sex cells have one complete set of chromosomes from the male or female parent. Sex cells, also called gametes, combine to produce somatic cells. Somatic cells, therefore, have twice as many chromosomes. The haploid number is...
cell. Such zygotes contain DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
derived from both the parents, and this provides all the genetic information necessary to form a new individual.
In land plants
Embryophyte
The land plants or embryophytes, more formally Embryophyta or Metaphyta, are the most familiar group of plants. They are called 'land plants' because they live primarily in terrestrial habitats, in contrast with the related green algae that are primarily aquatic. The embryophytes include trees,...
, the zygote is formed within a chamber called the archegonium
Archegonium
An archegonium , from the ancient Greek ἀρχή and γόνος , is a multicellular structure or organ of the gametophyte phase of certain plants, producing and containing the ovum or female gamete. The archegonium has a long neck canal and a swollen base...
. In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the sperm cell enters. As the zygote divides and grows, it does so within the archegonium.
In animal development, the term zygote is also used more loosely to refer to the group of cells formed by the first few cell divisions, although this is properly referred to as a morula
Morula
A morula is an embryo at an early stage of embryonic development, consisting of cells in a solid ball contained within the zona pellucida....
.
In mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian reproduction, after fertilization has taken place the zygote travels down the fallopian tube
Fallopian tube
The Fallopian tubes, also known as oviducts, uterine tubes, and salpinges are two very fine tubes lined with ciliated epithelia, leading from the ovaries of female mammals into the uterus, via the utero-tubal junction...
, while dividing to form more cells
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
without the zygote actually increasing in size. This cell division is mitotic
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, and is known as cleavage
Cleavage (embryo)
In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a...
. All mammals go through the zygote stage of life. Mammalian zygotes eventually develop into a blastocyst
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...
, after which they are more generally termed an embryo, and then a fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
.
A human zygote exists for about four days, and becomes a blastocyst
Blastocyst
The blastocyst is a structure formed in the early embryogenesis of mammals, after the formation of the morula. It is a specifically mammalian example of a blastula. It possesses an inner cell mass , or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast,...
on the fifth day.
In other species
A biparental zygote is a ChlamydomonasChlamydomonas
Chlamydomonas is a genus of green algae. They are unicellular flagellates. Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics...
(a kind of algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
) zygote that contains chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
DNA (cpDNA) from both parents.