The fertilized ovum resulting from the fusion of a male and a female gamete.
Zygote with Visible Nuclei of Egg and Sperm: This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
Image by TheVisualMD
Zygote
Zygote with Visible Nuclei of Egg and Sperm
Image by TheVisualMD
Zygote with Visible Nuclei of Egg and Sperm
Zygote with Visible Nuclei of Egg and Sperm: This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
Image by TheVisualMD
The Zygote
Zygote is a fertilized egg; a diploid cell resulting from the fertilization of haploid gametes from the male and female lines.
At the point of fertilization, the oocyte has not yet completed meiosis; all secondary oocytes remain arrested in metaphase of meiosis II until fertilization. Only upon fertilization does the oocyte complete meiosis. The unneeded complement of genetic material that results is stored in a second polar body that is eventually ejected. At this moment, the oocyte has become an ovum, the female haploid gamete. The two haploid nuclei derived from the sperm and oocyte and contained within the egg are referred to as pronuclei. They decondense, expand, and replicate their DNA in preparation for mitosis. The pronuclei then migrate toward each other, their nuclear envelopes disintegrate, and the male- and female-derived genetic material intermingles. This step completes the process of fertilization and results in a single-celled diploid zygote with all the genetic instructions it needs to develop into a human.
Most of the time, a woman releases a single egg during an ovulation cycle. However, in approximately 1 percent of ovulation cycles, two eggs are released and both are fertilized. Two zygotes form, implant, and develop, resulting in the birth of dizygotic (or fraternal) twins. Because dizygotic twins develop from two eggs fertilized by two sperm, they are no more identical than siblings born at different times.
Much less commonly, a zygote can divide into two separate offspring during early development. This results in the birth of monozygotic (or identical) twins. Although the zygote can split as early as the two-cell stage, splitting occurs most commonly during the early blastocyst stage, with roughly 70–100 cells present. These two scenarios are distinct from each other, in that the twin embryos that separated at the two-cell stage will have individual placentas, whereas twin embryos that form from separation at the blastocyst stage will share a placenta and a chorionic cavity.
Source: CNX OpenStax
Additional Materials (10)
Egg Cell Surrounded by Sperm Cell
Computer generated 3D visualization. This image reveals the egg cell surrounded by sperm cells (highlighted in blue). Of the approximately 300 million sperm that enter the upper part of the vagina, only 3 million enter the uterus and only one will penetrate the zona pellucida to fertilize the egg. When the parental genes fuse, a zygote is formed.
Zygote: egg cell after fertilization with a sperm. The male and female pronuclei are converging, but the genetic material is not yet united.
Zygote: egg cell after fertilization with a sperm. The male and female pronuclei are converging, but the genetic material is not yet united.
Image by Nina Sesina
Zygote with Visible Nuclei of Egg and Sperm: This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
Zygote with Visible Nuclei of Egg and Sperm: This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
Image by TheVisualMD
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Zygote as Result of Fertilization
Formation of a zygote. View is from within the cytoplasm of an oocyte. The nucleus of the sperm, which contains 23 paternal chromosomes, fuses with the nucleus of the ovum, containing 23 maternal chromosomes, to restore the diploid number (46 chromosomes) therefore creating a diploid zygote. Once the fusion is complete, fertilization is complete.
Video by TheVisualMD
This browser does not support the video element.
Zygote Formation
Formation of a zygote. View is from within the cytoplasm of an oocyte. The nucleus of the sperm, which contains 23 paternal chromosomes, is about to fuse with the nucleus of the ovum, which contains 23 maternal chromosomes, to restore the diploid number (46 chromosomes) therefore creating a diploid zygote. Once the fusion is complete, fertilization is complete.
Video by TheVisualMD
This browser does not support the video element.
Zygote Cleavage
Video of a couple preparing to lie in bed. Once female is lying down, camera zooms into her pelvic area to show a zygote undergoing embryonic cleavage to form a morula. The morula travels through her fallopian tube on its way to the uterus.
Video by TheVisualMD
Zygote Formed After Fertilization
At conception, a zygote is formed from the union of the mother's egg and the father's sperm.
Image by TheVisualMD
This browser does not support the video element.
Formation of Zygote
Close up of a sperm penetrating the zona pellucida to gain access into the cytoplasm of the oocyte. The camera zooms into the ooctye. Once the sperm gains access into to oocyte, it degenerates until only the nucleus and centrioles remain. The nucleus of the sperm fuses with the nucleus of the ovum to restore the diploid number (46 chromosomes) therefore creating a diploid zygote. Once the fusion is complete, fertilization is complete.
Video by TheVisualMD
Sperm and Oocyte During Fertilization
Computer Generated Image from Micro-MRI, actual size of zygote = 0.1 mm - This image captures the moment of fertilization, when a sperm breaks through the oocyte's outer shell and breaches the inner membrane. Once fertilized, the egg becomes a zygote, which then begins its 3-day descent to the uterus via the fallopian tubes.
Zygote: egg cell after fertilization with a sperm. The male and female pronuclei are converging, but the genetic material is not yet united.
Nina Sesina
Zygote with Visible Nuclei of Egg and Sperm: This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
TheVisualMD
0:09
Zygote as Result of Fertilization
TheVisualMD
0:14
Zygote Formation
TheVisualMD
0:39
Zygote Cleavage
TheVisualMD
Zygote Formed After Fertilization
TheVisualMD
0:39
Formation of Zygote
TheVisualMD
Sperm and Oocyte During Fertilization
TheVisualMD
Fertilization
Zygote Formed After Fertilization
Image by TheVisualMD
Zygote Formed After Fertilization
At conception, a zygote is formed from the union of the mother's egg and the father's sperm.
Image by TheVisualMD
Fertilization - Zygote
The process in which an organism develops from a single-celled zygote to a multi-cellular organism is complex and well-regulated. The early stages of embryonic development are also crucial for ensuring the fitness of the organism.
Fertilization, pictured in Figure a is the process in which gametes (an egg and sperm) fuse to form a zygote. The egg and sperm each contain one set of chromosomes. To ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. In mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. When a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. In placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in Figure b. The fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. The nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.
(a) Fertilization is the process in which sperm and egg fuse to form a zygote. (b) Acrosomal reactions help the sperm degrade the glycoprotein matrix protecting the egg and allow the sperm to transfer its nucleus. (credit: (b) modification of work by Mariana Ruiz Villareal; scale-bar data from Matt Russell)
To ensure that no more than one sperm fertilizes the egg, once the acrosomal reactions take place at one location of the egg membrane, the egg releases proteins in other locations to prevent other sperm from fusing with the egg. If this mechanism fails, multiple sperm can fuse with the egg, resulting inpolyspermy. The resulting embryo is not genetically viable and dies within a few days.
Sperm and the Process of Fertilization
Before fertilization, hundreds of capacitated sperm must break through the surrounding corona radiata and zona pellucida so that one can contact and fuse with the oocyte plasma membrane.
Source: CNX OpenStax
Additional Materials (2)
Zygote with Visible Nuclei of Egg and Sperm
Computer Generated Image from Micro-MRI, actual size of egg = 0.1 mm in diameter - This image presents the formation of a zygote, a result of fertilization. The nuclei of the egg and sperm can be seen in this image, as indicated by the two circles inside the egg.
Image by TheVisualMD
Embrology - Day 0 7 Fertilization, Zygote, Blastocyst
Video by Armando Hasudungan/YouTube
Zygote with Visible Nuclei of Egg and Sperm
TheVisualMD
4:00
Embrology - Day 0 7 Fertilization, Zygote, Blastocyst
Armando Hasudungan/YouTube
Cleavage and Blastula Stage
Blastocyst in Uterine Wall
Image by TheVisualMD
Blastocyst in Uterine Wall
Having secured a home and a food supply, the blastocyst doubles in size every day.
Image by TheVisualMD
Cleavage and Blastula Stage
The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. Cleavage is illustrated in (Figure 43.24a). After the cleavage has produced over 100 cells, the embryo is called a blastula. The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel). Mammals at this stage form a structure called the blastocyst, characterized by an inner cell mass that is distinct from the surrounding blastula, shown in Figure 43.24b. During cleavage, the cells divide without an increase in mass; that is, one large single-celled zygote divides into multiple smaller cells. Each cell within the blastula is called a blastomere.
Figure 43.24 (a) During cleavage, the zygote rapidly divides into multiple cells without increasing in size. (b) The cells rearrange themselves to form a hollow ball with a fluid-filled or yolk-filled cavity called the blastula.
Cleavage can take place in two ways: holoblastic (total) cleavage or meroblastic (partial) cleavage. The type of cleavage depends on the amount of yolk in the eggs. In placental mammals (including humans) where nourishment is provided by the parent’s body, the eggs have a very small amount of yolk and undergo holoblastic cleavage. Other species, such as birds, with a lot of yolk in the egg to nourish the embryo during development, undergo meroblastic cleavage.
In mammals, the blastula forms the blastocyst in the next stage of development. Here the cells in the blastula arrange themselves in two layers: the inner cell mass, and an outer layer called the trophoblast. The inner cell mass is also known as the embryoblast and this mass of cells will go on to form the embryo. At this stage of development, illustrated in Figure 43.25 the inner cell mass consists of embryonic stem cells that will differentiate into the different cell types needed by the organism. The trophoblast will contribute to the placenta and nourish the embryo.
Figure 43.25 The rearrangement of the cells in the mammalian blastula to two layers—the inner cell mass and the trophoblast—results in the formation of the blastocyst.
Source: CNX OpenStax
Additional Materials (5)
This browser does not support the video element.
Cleavage in Developing Embryo
Being shown is the embryonic cleavage or rapid division of a zygote to form a multicellular morula. A morula is an embryo at an early stage of embryonic development, consisting of approximately 12-32 cells (blastomeres) in a sold ball contained within the zona pellucida.
Video by TheVisualMD
Blastula
This image shows the process of gastrulation. Gastrulation occurs when a blastula, made up of one layer, folds inward and enlarges to create a gastrula. A gastrula has 3 germ layers--the ectoderm, the mesoderm, and the endoderm. Some of the ectoderm cells from the blastula collapse inward and form the endoderm. The blastospore is the hole created in this action. Whether this blastospore develops into a mouth or an anus determines whether the organism is a protostome or a dueterostome. This diagram is color coded. Ectoderm, blue. Endoderm, green. Blastocoel (the yolk sack), yellow. Archenteron (the gut), purple.
Image by Abigail Pyne
Fertilization and Early Embryonic Development
The rearrangement of the cells in the mammalian blastula to two layers—the inner cell mass and the trophoblast—results in the formation of the blastocyst.
Image by CNX Openstax
Fertilization and Early Embryonic Development
Image by CNX Openstax
Human embryogenesis
The initial stages of human embryogenesis.
Image by Zephyris
0:25
Cleavage in Developing Embryo
TheVisualMD
Blastula
Abigail Pyne
Fertilization and Early Embryonic Development
CNX Openstax
Fertilization and Early Embryonic Development
CNX Openstax
Human embryogenesis
Zephyris
Pre-Implantation Embryonic Development
Human embryogenesis
Image by Minami Himemiya
Human embryogenesis
Embryos, 2 and 4-cell stages
Image by Minami Himemiya
Pre-Implantation Embryonic Development
Cleavage is a form of mitotic cell division in which the cell divides but the total volume remains unchanged; this process serves to produce smaller and smaller cells
Pre-implantation Embryonic Development
Following fertilization, the zygote and its associated membranes, together referred to as the conceptus, continue to be projected toward the uterus by peristalsis and beating cilia. During its journey to the uterus, the zygote undergoes five or six rapid mitotic cell divisions. Although each cleavage results in more cells, it does not increase the total volume of the conceptus (Figure). Each daughter cell produced by cleavage is called a blastomere (blastos = "germ," in the sense of a seed or sprout).
Approximately 3 days after fertilization, a 16-cell conceptus reaches the uterus. The cells that had been loosely grouped are now compacted and look more like a solid mass. The name given to this structure is the morula (morula = "little mulberry"). Once inside the uterus, the conceptus floats freely for several more days. It continues to divide, creating a ball of approximately 100 cells, and consuming nutritive endometrial secretions called uterine milk while the uterine lining thickens. The ball of now tightly bound cells starts to secrete fluid and organize themselves around a fluid-filled cavity, the blastocoel. At this developmental stage, the conceptus is referred to as a blastocyst. Within this structure, a group of cells forms into an inner cell mass, which is fated to become the embryo. The cells that form the outer shell are called trophoblasts (trophe = "to feed" or "to nourish"). These cells will develop into the chorionic sac and the fetal portion of the placenta (the organ of nutrient, waste, and gas exchange between mother and the developing offspring).
The inner mass of embryonic cells is totipotent during this stage, meaning that each cell has the potential to differentiate into any cell type in the human body. Totipotency lasts for only a few days before the cells' fates are set as being the precursors to a specific lineage of cells.
Pre-Embryonic Cleavages
Pre-embryonic cleavages make use of the abundant cytoplasm of the conceptus as the cells rapidly divide without changing the total volume.
As the blastocyst forms, the trophoblast excretes enzymes that begin to degrade the zona pellucida. In a process called "hatching," the conceptus breaks free of the zona pellucida in preparation for implantation.
Source: CNX OpenStax
Additional Materials (8)
This browser does not support the video element.
Cleavage in Developing Embryo
Being shown is the embryonic cleavage or rapid division of a zygote to form a multicellular morula. A morula is an embryo at an early stage of embryonic development, consisting of approximately 12-32 cells (blastomeres) in a sold ball contained within the zona pellucida.
Early embryogenesis - Cleavage, blastulation, gastrulation, and neurulation | MCAT | Khan Academy
khanacademymedicine/YouTube
7:11
The Peptide Bond: Formation and Cleavage
khanacademymedicine/YouTube
4:00
Embrology - Day 0 7 Fertilization, Zygote, Blastocyst
Armando Hasudungan/YouTube
1:18:15
Embryology animation fertilization to development of the nervous system everything in one place.
RedMedBd/YouTube
1:43
What Happens After Fertilization? Human Embryo Development Animation Video - Blastocyst Implantation
Science Art/YouTube
Life Cycles of Sexually Reproducing Organisms
Why sexual reproduction (faster variation) | How do organisms reproduce | Biology | Khan Academy
Video by Khan Academy India - English/YouTube
Why sexual reproduction (faster variation) | How do organisms reproduce | Biology | Khan Academy
Video by Khan Academy India - English/YouTube
Life Cycles of Sexually Reproducing Organisms
Haploid-dominant is a life-cycle type in which the multicellular haploid stage is prevalent.
Gametophyte is a multicellular haploid life-cycle stage that produces gametes.
Germ cell is a specialized cell that produces gametes, such as eggs or sperm.
Fertilization and meiosis alternate in sexual life cycles. What happens between these two events depends on the organism. The process of meiosis reduces the resulting gamete’s chromosome number by half. Fertilization, the joining of two haploid gametes, restores the diploid condition. There are three main categories of life cycles in multicellular organisms: diploid-dominant, in which the multicellular diploid stage is the most obvious life stage (and there is no multicellular haploid stage), as with most animals including humans; haploid-dominant, in which the multicellular haploid stage is the most obvious life stage (and there is no multicellular diploid stage), as with all fungi and some algae; and alternation of generations, in which the two stages, haploid and diploid, are apparent to one degree or another depending on the group, as with plants and some algae.
Nearly all animals employ a diploid-dominant life-cycle strategy in which the only haploid cells produced by the organism are the gametes. The gametes are produced from diploid germ cells, a special cell line that only produces gametes. Once the haploid gametes are formed, they lose the ability to divide again. There is no multicellular haploid life stage. Fertilization occurs with the fusion of two gametes, usually from different individuals, restoring the diploid state (Figurea).
VISUAL CONNECTION
(a) In animals, sexually reproducing adults form haploid gametes from diploid germ cells. (b) Fungi, such as black bread mold (Rhizopus nigricans), have haploid-dominant life cycles. (c) Plants have a life cycle that alternates between a multicellular haploid organism and a multicellular diploid organism. (credit c “fern”: modification of work by Cory Zanker; credit c “gametophyte”: modification of work by “Vlmastra”/Wikimedia Commons)
If a mutation occurs so that a fungus is no longer able to produce a minus mating type, will it still be able to reproduce?
Most fungi and algae employ a life-cycle strategy in which the multicellular “body” of the organism is haploid. During sexual reproduction, specialized haploid cells from two individuals join to form a diploid zygote. The zygote immediately undergoes meiosis to form four haploid cells called spores (Figureb).
The third life-cycle type, employed by some algae and all plants, is called alternation of generations. These species have both haploid and diploid multicellular organisms as part of their life cycle. The haploid multicellular plants are called gametophytes because they produce gametes. Meiosis is not involved in the production of gametes in this case, as the organism that produces gametes is already haploid. Fertilization between the gametes forms a diploid zygote. The zygote will undergo many rounds of mitosis and give rise to a diploid multicellular plant called a sporophyte. Specialized cells of the sporophyte will undergo meiosis and produce haploid spores. The spores will develop into the gametophytes (Figurec).
Summary
Nearly all eukaryotes undergo sexual reproduction. The variation introduced into the reproductive cells by meiosis appears to be one of the advantages of sexual reproduction that has made it so successful. Meiosis and fertilization alternate in sexual life cycles. The process of meiosis produces genetically unique reproductive cells called gametes, which have half the number of chromosomes as the parent cell. Fertilization, the fusion of haploid gametes from two individuals, restores the diploid condition. Thus, sexually reproducing organisms alternate between haploid and diploid stages. However, the ways in which reproductive cells are produced and the timing between meiosis and fertilization vary greatly. There are three main categories of life cycles: diploid-dominant, demonstrated by most animals; haploid-dominant, demonstrated by all fungi and some algae; and alternation of generations, demonstrated by plants and some algae.
Source: CNX OpenStax
Additional Materials (42)
Sex Differentiation
Video by Armando Hasudungan/YouTube
Indifferent Penis of Human Embryo (Week 9 Gestational Age, Week 7 Fetal Age)
Medical visualization of an embryonic indifferent penis at 7 weeks. The external genitalia of men and women are derived from the same (homologous) tissues. Shown are the genital tubercle (which will become the penis or the clitoris), urogenital groove and sinus (which will become the bladder and urethra, and also forms the vagina and hymen), labioscrotal folds (which will form the scrotum or the labia majora), and anal groove. These indifferent structures form by the end of the 7th week of development, and fully differentiate into male or female by week 12.
Image by TheVisualMD
Sexual Differentiation
Differentiation of the male and female reproductive systems does not occur until the fetal period of development.
Image by CNX Openstax
Sexual differentiation
Differentiation of the male and female reproductive systems does not occur until the fetal period of development.
Image by OpenStax College
Sexual differentiation
Sexual differentiation. The human embryo has indifferent sex accessory ducts until the seventh week of development.
Image by Jonathan.Marcus
Sexual Reproduction
In animals, sexually reproducing adults form haploid gametes from diploid germ cells. Fusion of the gametes gives rise to a fertilized egg cell, or zygote. The zygote will undergo multiple rounds of mitosis to produce a multicellular offspring. The germ cells are generated early in the development of the zygote.
Image by CNX Openstax
Effects of LH on the body
The Hormones that trigger growth and puberty
Image by OpenStax College
Clitoris
The internal and external parts of the clitoris.
Image by Fbot
Penile-Clitoral Structure
Comparative diagram of the internal structure of the human glans penis and glans clitoridis.
Image by Esseh
Male reproductive system
Reproductive (Male)
Image by OpenStax College
Human Reproductive Anatomy and Gametogenesis
The reproductive structures of the human female are shown. (credit a: modification of work by Gray's Anatomy; credit b: modification of work by CDC)
Image by CNX Openstax (credit a: modification of work by Gray's Anatomy; credit b: modification of work by CDC)
Stages of Development
During the fetal stage, the baby's brain develops and the body adds size and weight, until the fetus reaches full-term development.
Image by CNX Openstax
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External Genitalia of a 12 Week Old (Week 13 Gestational Age, Week 12 Fetal Age) Male Fetus
Photograph of external genitalia of a 12 week old male fetus. The age is calculated from the day of fertilization. Up until 5 weeks after fertilization, the embryonic sex organs in males and females are essentially identical. Genetically, sex has been assigned but the external structures remain indifferent. During the third month, the external genitalia starts to differentiate. The formation of external genitalia that distinguishes between the male and the female sexes begins at the end of the ninth week of fetal development. The female structures include the labia, clitoris, and urethral orifice.
Image by TheVisualMD
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External Genitalia of a 12 Week Old (Week 13 Gestational Age, Week 12 Fetal Age) Male Fetus
Photograph of external genitalia of a 12 week old male fetus. The age is calculated from the day of fertilization. Up until 5 weeks after fertilization, the embryonic sex organs in males and females are essentially identical. Genetically, sex has been assigned but the external structures remain indifferent. During the third month, the external genitalia starts to differentiate. The formation of external genitalia that distinguishes between the male and the female sexes begins at the end of the ninth week of fetal development. The reddish indentation shown above the genitalia is the anus, the opening for solid waste. The external genitalia, seen from the backside, is comprised of the penis, scrotum, and urethra masculina.
Image by TheVisualMD
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External Genitalia of a 12 Week Old (Week 13 Gestational Age, Week 12 Fetal Age) Male Fetus
Photograph of external genitalia of a 12 week old male fetus. The age is calculated from the day of fertilization. Up until 5 weeks after fertilization, the embryonic sex organs in males and females are essentially identical. Genetically, sex has been assigned but the external structures remain indifferent. During the third month, the external genitalia starts to differentiate. The formation of external genitalia that distinguishes between the male and the female sexes begins at the end of the ninth week of fetal development. The reddish indentation shown above the genitalia is the anus, the opening for solid waste. The external genitalia, seen from the backside, is comprised of the penis, scrotum, and urethra masculina.
Image by TheVisualMD
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External Genitalia of a 12 Week Old (13 Weeks Gestational Age, 12 Weeks Fetal Age) Male Fetus
Photograph of external genitalia of a 12 week old male fetus. The age is calculated from the day of fertilization. Up until 5 weeks after fertilization, the embryonic sex organs in males and females are essentially identical. Genetically, sex has been assigned but the external structures remain indifferent. During the third month, the external genitalia starts to differentiate. The formation of external genitalia that distinguishes between the male and the female sexes begins at the end of the ninth week of fetal development. The reddish indentation shown above the genitalia is the anus, the opening for solid waste. The external genitalia, seen from the backside, is comprised of the penis, scrotum, and urethra masculina.
Image by TheVisualMD
Human Male and Female with Pregnancy
3D visualization reconstructed from scanned human data of the male, female and fetal endocrine systems. The endocrine system is the regulator of the human body as it responsible for maintaining homeostasis by producing and directing chemical messengers called hormones. Hormones act on just about every cell to carry out a variety of functions related to the following: metabolism, water and mineral balance, sexual development, growth, and stress reactions. Most hormones travel throughout the body via the bloodstream to affect their target organs and tissues. Other hormones act locally and arrive at their site of action via microcirculation.
Image by TheVisualMD
Erection
Illustration of Erectile Tissue : Three columns of erectile tissue make up most of the volume of the penis.
Image by OpenStax College
Woman pregnancy month by month
Woman pregnancy month by month.
Image by Month_1.svg: Miraceti derivative work: Waglione (talk)
Human Fertilization
Human Fertilization. The sperm and ovum unite through fertilization, creating a zygote that (over the course of 8-9 days) will implant in the uterine wall, where it will reside over the course of 9 months.
Image by Ttrue12
Pregnancy
Illustration of Size of Uterus Throughout Pregnancy
Image by OpenStax College
Pregnancy
Pregnant the day we know it's a boy
Image by Naoll
Sperm
The process of spermatogenesis as the cells progress from spermatogium, to primary spermatocytes, to secondary spermatocytes, to spermatids and to Sperm.
Image by OpenStax College
Newborn
A single fertilized egg develops over the span of nine months into an infant consisting of trillions of cells and capable of surviving outside the womb. (credit: “Seattleye”/flickr.com)
Image by CNX Openstax (credit: “Seattleye”/flickr.com)
The Process of Meiosis
Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes.
Image by CNX Openstax
Reproductive Development and Structure
Pollen develops from the microspore mother cells. The mature pollen grain is composed of two cells: the pollen tube cell and the generative cell, which is inside the tube cell. The pollen grain has two coverings: an inner layer (intine) and an outer layer (exine). The inset scanning electron micrograph shows Arabidopsis lyrata pollen grains. (credit “pollen micrograph”: modification of work by Robert R. Wise; scale-bar data from Matt Russell)
Image by CNX Openstax
Human Reproductive Anatomy and Gametogenesis
The reproductive structures of the human male are shown.
Image by CNX Openstax
Human Reproductive Anatomy and Gametogenesis
During spermatogenesis, four sperm result from each primary spermatocyte.
Image by CNX Openstax
Human Reproductive Anatomy and Gametogenesis
Oocytes develop in (a) follicles, located in the ovary. At the beginning of the menstrual cycle, the follicle matures. At ovulation, the follicle ruptures, releasing the egg. The follicle becomes a corpus luteum, which eventually degenerates. The (b) follicle in this light micrograph has an oocyte at its center. (credit a: modification of work by NIH; scale-bar data from Matt Russell)
Image by CNX Openstax
Human Reproductive Anatomy and Gametogenesis
Human sperm, visualized using scanning electron microscopy, have a flagellum, neck, and head. (credit b: modification of work by Mariana Ruiz Villareal; scale-bar data from Matt Russell)
Image by CNX Openstax (credit b: modification of work by Mariana Ruiz Villareal; scale-bar data from Matt Russell)
Human Reproductive Anatomy and Gametogenesis
The process of oogenesis occurs in the ovary’s outermost layer.
Image by CNX Openstax
Week 39 of Pregnancy
The womb is a very cramped space for a full-term baby.
Image by TheVisualMD
Stages of Development
Sperm and ovum fuse at the point of conception.
Image by CNX Openstax
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External Genitalia of 11 Week Old Female Fetus
Medical visualization of female fetal external genitalia at 11 weeks. Because of a lack of stimulation by androgens, the indifferent structures of the genital tubercle, urogenital groove and sinus, and the labioscrotal folds have nearly completed their transformation into the female sex organs-the clitoris, urethra, vagina, and labia.
Image by TheVisualMD
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External Genitalia of 9 Week Old Male Fetus
Medical visualization of male fetal external genitalia at 9 weeks. Because of stimulation by androgens, the indifferent structures of the genital tubercle, urogenital groove and sinus, and the labioscrotal folds have nearly completed their transformation into the male sex organs-the penis, urethra, and scrotum.
Image by TheVisualMD
Embryonic Development, DNA and Chromosomal Mix
Image by TheVisualMD
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From Conception to Birth
Explore and uncover the miraculous story of a new life forming. Conception begins when a male reproductive cell (sperm cell), successfully fuses with the female reproductive cell (egg cell). After the fusion of the sperm and egg is the fusion of their genetic materials. Cell division follows. The zygote (cell formed by the fusion of the sperm and egg) divides into two, four, eight, and so on. Changes happen in every stage of embryonic development. At 25 days, the embryo curves into C-shape and the arches that form the face and neck are becoming evident under the enlarging forebrain. The primitive heart is beating. The development of the limb buds are also visible, and the hand plates are noticeable in day 44. At 56 days, the circulatory system is given an emphasis as well as the developed organs of the embryo: the brain, heart, umbilical cord, vertebrae, stomach, kidneys, lungs, and liver. At this stage, all the major organs are in place. The genitalia of a 56 day old fetus inside womb is visible. Though the indifferent penis is visible, the sex of the baby is not clear from external appearance until week 12. At 7 months, it is noticeable that the fetus is in fetal position where the legs are drawn up, because of the limited space in the uterus. The arms, legs, and toenails are fully formed. At 9 months, the skull can be seen showing the unconnected bony plates called fontanels. These fontanels are significant for fetal brain's protection and they allow the head to elongate and mold during childbirth, then return to a rounded shape. At 9 months, the baby is ready for delivery. The baby in position for birth, the baby then rotates down, pushes out and comes out headfirst. In order to squeeze the baby through the pelvic canal, the mother's bones pop open in the middle.