In humans, the zygote is the first cell stage of pregnancy. It is located first in the fallopian tube and moves towards the uterus. As the zygote travels, it divides to give rise to cells that will also undergo mitosis.
Soon, the zygote will transition into an embryo that will be implanted in the uterus. There, the embryo will develop further into a fetus. For more info and facts on human development, read the Developmental Biology Tutorials. These tutorials describe how a living thing grows and attains maturity. In many fungi and protists, the fusion of the nuclei of haploid cells produces a diploid zygote, called zygospore.
In fungi, the zygospores are found in the zygosporangia. In algae, the zygospores occur as a cell following the fusion of unicellular gametes. Watch this video below to know the different stages that a human zygote goes through to becoming an embryo.
For human species to obviate extinction, reproductive mature adults should be producing viable offspring in order to continue the existence of the species and pass on genetic information from generation to generation.
Read this tutorial to learn more about human reproduction and fertilization Read More. Plants are characterized by having alternation of generations in their life cycles.
This tutorial is a review of plant mitosis, meiosis, and alternation of generations. Developmental biology is a biological science that is primarily concerned with how a living thing grows and attains maturity. The tutorials included here focuses on human growth and development. Thus, one can expect to learn about human zygote developing and maturing into adulthood after these tutorials. Also included here are informative guides on dietary sources..
Seed plants are vascular plants. They differ from the other vascular plants in producing seeds that germinate into a new plant. Two major plant divisions are covered: the angiosperms and the gymnosperms. Humans are capable of only one mode of reproduction, i.
Haploid sex cells gametes are produced so that at fertilization a diploid zygote forms. This tutorial is an in-depth study guide regarding male and female reproductive physiology Upon fertilization, a zygote forms and develops into an embryo. This tutorial elaborates on the growth and development from zygote to embryo and ultimately to a human baby.
Developmental Biology. The fertilized egg zygote divides repeatedly as it moves down the fallopian tube to the uterus. First, the zygote becomes a solid ball of cells. Then it becomes a hollow ball of cells called a blastocyst. Inside the uterus, the blastocyst implants in the wall of the uterus, where it develops into an embryo attached to a placenta and surrounded by fluid-filled membranes.
About 6 days after fertilization, the blastocyst attaches to the lining of the uterus, usually near the top. This process, called implantation, is completed by day 9 or The wall of the blastocyst is one cell thick except in one area, where it is three to four cells thick. The inner cells in the thickened area develop into the embryo, and the outer cells burrow into the wall of the uterus and develop into the placenta.
The placenta produces several hormones that help maintain the pregnancy. For example, the placenta produces human chorionic gonadotropin, which prevents the ovaries from releasing eggs and stimulates the ovaries to produce estrogen and progesterone continuously. The placenta also carries oxygen and nutrients from mother to fetus and waste materials from fetus to mother. Some of the cells from the placenta develop into an outer layer of membranes chorion around the developing blastocyst.
Other cells develop into an inner layer of membranes amnion , which form the amniotic sac. When the sac is formed by about day 10 to 12 , the blastocyst is considered an embryo. The amniotic sac fills with a clear liquid amniotic fluid and expands to envelop the developing embryo, which floats within it.
The next stage in development is the embryo, which develops within the amniotic sac, under the lining of the uterus on one side. This stage is characterized by the formation of most internal organs and external body structures. Most organs begin to form about 3 weeks after fertilization, which equals 5 weeks of pregnancy because doctors date pregnancy from the first day of the woman's last menstrual period, which is typically 2 weeks before fertilization. At this time, the embryo elongates, first suggesting a human shape.
Shortly thereafter, the area that will become the brain and spinal cord neural tube begins to develop. The heart and major blood vessels begin to develop earlier—by about day The heart begins to pump fluid through blood vessels by day 20, and the first red blood cells appear the next day. Blood vessels continue to develop in the embryo and placenta. Almost all organs are completely formed by about 10 weeks after fertilization which equals 12 weeks of pregnancy.
Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic total or meroblastic partial. Cell cleavage : Early development is characterized by cleavage of the zygote, which refers to cell divisions that are not associated with significant growth of the embryo. Holoblastic cleavage occurs in animals with little yolk in their eggs. These species, such as humans and other mammals, receive nourishment as embryos from the mother via the placenta or milk after birth.
On the other hand, meroblastic cleavage occurs in animals whose eggs have more yolk, such as birds and oviparous reptiles although some viviparous reptiles also exist. Since cleavage is impeded by the vegetal pole, there is a very uneven distribution and size of cells. Cells are more numerous and smaller at the animal pole of the zygote than at the vegetal pole. In holoblastic eggs, the first cleavage always occurs along the vegetal—animal axis of the egg, and the second cleavage is perpendicular to the first.
From here, the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage in various organisms.
The end of cleavage is known as the midblastula transition and coincides with the onset of zygotic transcription.
In amniotes, the cells of the morula are at first closely aggregated. However, they quickly become arranged into an outer or peripheral layer, the trophoblast, and an inner cell mass. The trophoblast does not contribute to the formation of the embryo proper; the embryo develops from the inner cell mass.
Fluid collects between the trophoblast and the greater part of the inner cell mass, and thus the morula, is converted into the blastodermic vesicle also called the blastocyst or blastula. The inner cell mass remains in contact with the trophoblast at one pole of the ovum. This is named the embryonic pole, since it indicates the location where the future embryo will develop.
In the case of monozygotic twins derived from one zygote , a zygote divides into two separate cells embryos at the first cleavage division. Monozygotic twins can also develop from two inner cell masses. A rare occurrence is the division of a single inner cells mass giving rise to twins.
However, if one inner cell mass divides incompletely, the result is conjoined twins. Dizygotic twins is the development of two embryos from two different zygotes. The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta. In humans, the blastocyst is formed approximatelyy five days after fertilization.
This stage is preceded by the morula. The morula is a solid ball of about 16 undifferentiated, spherical cells. As cell division continues in the morula, the blastomeres change their shape and tightly align themselves against each other.
This is called compaction and is likely mediated by cell surface adhesion glycoproteins. Only one lucky one will get in. Once it does, chemical changes in the egg itself occur so that no other sperm can break through. A zygote is formed. Sometimes, your ovaries release more than one egg. If both become fertilized, then congrats! Women with moms or sisters who have had these types of twins are about twice as likely to have them themselves.
In intrauterine insemination IUI , a doctor uses a thin catheter to inject sperm directly into your uterus to increase the chances that sperm will meet the egg. During in vitro fertilization IVF , your eggs are fertilized by sperm in a laboratory at a fertility clinic. Then at least one embryo is transferred into your uterus with the hope that it will spark at least one and possibly more!
It takes about five to six days for a zygote to transform into a blastocyst a microscopic ball of cells and then into an embryo. Within hours after sperm meets egg, the zygote divides and then continues to divide and divide. The blastocyst now begins its big journey from your fallopian tube to your uterus. Very rarely — about three or four out of 1, births — the zygote splits in half, leading to two embryos. Since the original egg was fertilized by one sperm, the genetic material in both embryos is identical, resulting in you guessed it identical twins.
0コメント