Processes of cell division, differentiation, and specialization
Reproductive system-Gametogenesis by meiosis
Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
Gastrulation leads to the formation of the three germ layers that give rise to the different organs in the animal body, a process called organogenesis. The embryo becomes the fetus that grows inside the uterus and further develops and continues until birth. Different organs take part in the development of the many organ systems of the body. Sometimes full development, as in the lungs, continues after birth.
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation-Key Points
Ovum and sperm play an essential role in the reproduction process but differ in terms of the formation, morphology, and relative contribution to the next generation. The formation during developmental stages of gametogenesis, specifically in meiosis, vary in male and female. Sperm is the male gamete which is long, motile, flagellated cell and is differentiated into head, neck, middle piece and tail, though they are comparatively smaller in size; the ovum is the female gamete, where the cells are rounded spheres and non-motile, though not differentiated into different parts, and the cells are larger in comparison to the sperm cell. Ovum and sperm differ in their relative contribution to the next generation, such that sperm only contributes to DNA. In contrast, egg contributes to the production of DNA, epigenetics, and other organelles.
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation
Ovum and sperm play an essential role in the reproduction process, where the participation of both the opposite gametes is equally significant and necessary. However, they differ in terms of the formation, morphology, and their relative contribution to the next generation.
Reproductive system-Gametogenesis by meiosis
During Prophase I of Meiosis I, homologous chromosomes come together and intertwine in a process called synapsis. At this point, each chromosome consists of two sister chromatids so each synaptic pair contains four chromatids and is referred to as a tetrad. Chromatids of homologous chromosomes may break at the point of synapsis, called the chiasma or chiasmata and exchange equivalent pieces of DNA. This process is called crossing over. Occurs between homologous chromosomes and not sister chromatids of the same chromosome. Recombination can unlink linked genes thereby increasing the variety of genetic recombinations that can be produced via gametogenesis. Linkage refers to the tendency of genes close together to be inherited together. Genes that are further apart are more likely to under go crossing over and less likely to be inherited together. Crossing over explains Mendel's second law (of independent assortment) which states that the inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes.
Reproductive system-Gametogenesis by meiosis
During anaphase 1, homologous chromosomes separate and are pulled to opposite poles of the cell in a process referred to as disjunction. This agrees with Mendel's first law of segregation. During disjunction, each chromosome of paternal origin separates (or disjoins) from its homologue of maternal origin and either chromosomes can end up in either daughter cells. During telophase, there may be a short rest period, or interkinesis during which the chromosomes partially uncoil.
Reproductive system-Gametogenesis by meiosis
During meiosis, two cell divisions separate the paired chromosomes in the nucleus. They then separate the chromatids that were made during an earlier stage of the cell's life cycle, resulting in gametes that each contain half the number of chromosomes as the parent. The production of eggs and sperm are called oogenesis and spermatogenesis, respectively. Meiosis I results in homologous chromosomes being separated, generating haploid daughter cells; this is known as reductional division. Meiosis II is similar to mitosis, in that it results in the separation of sister chromatids, and is known as equational division.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
During pregnancy, the unborn baby (fetus) depends on its mother for nourishment and oxygen. Since the fetus doesn't breathe air, his or her blood circulates differently than it does after birth. At birth, significant changes take place. The umbilical cord is clamped, and the baby no longer receives oxygen and nutrients from the mother. With the first breaths of air, the lungs start to expand, and the lungs' ducts both close. The baby's circulation and blood flow through the heart now function like an adult's. See photo @jackwestin.com.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth-Key Points
Fertilization involves the union of the sperm and egg cells in the fallopian tubes. After fertilization, cell division starts to form the developing embryo in stages, including the morula and then the blastula. Implantation of the embryo takes place in the endometrium of the uterus. Organogenesis is the formation of organs from the germ layer, which gives rise to specific tissue types.
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation
Furthermore, they also differ in their relative contribution to the next generation. Sperm only contributes to DNA (the egg actively destroys sperm mitochondria) while egg contributes to the production of DNA, mitochondria, organelles and epigenetic inheritance. See photo @jackwestin.com.
Reproductive system-Gametogenesis by meiosis-Key Points
Gametogenesis, the production of sperm (spermatogenesis) and eggs (oogenesis), takes place through the process of meiosis. In oogenesis, diploid oogonium goes through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest; it will finish this division as it grows in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body. The secondary oocyte begins the second meiotic division and then arrests again; it will not finish this division unless a sperm fertilizes it, and then produces a mature ovum and another polar body.
Reproductive system-Gametogenesis by meiosis-Key Points
In spermatogenesis, diploid spermatogonia go through mitosis until they begin to develop into gametes; eventually, one develops into a primary spermatocyte that will go through the first meiotic division to form two haploid secondary spermatocytes. The secondary spermatocytes will go through a second meiotic division to each produce two spermatids; these cells will eventually develop flagella and become mature sperm.
Reproductive system-Gametogenesis by meiosis
Meiosis begins with a cell called a primary spermatocyte. At the end of the first meiotic division, a haploid cell called a secondary spermatocyte is produced. This haploid cell must go through another meiotic cell division. When the spermatid (cell produced at the end of meiosis) reaches the lumen of the tubule and grows a flagellum (or "tail"), it is called a sperm cell. Four sperms result from each primary spermatocyte that goes through meiosis. See photo @jackwestin.com.
Reproductive system-Gametogenesis by meiosis
Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis starts with a germ cell, called an oogonium (plural: oogonia). Still, this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.
Reproductive system-Gametogenesis by meiosis
Oogenesis. A primary oocyte begins the first meiotic division but then arrests until later in life when it will finish this division in a developing follicle. This results in a secondary oocyte, which will complete meiosis if it is fertilized.
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation
Ovum (female gamete) and sperm (male gamete) are necessary for the reproduction process but they differ in formation, morphology, and relative contribution to the next generation.
Reproductive system-Gametogenesis by meiosis
The cell starting meiosis is called a primary oocyte. This cell will begin the first meiotic division, but be arrested in its progress in the prophase I stage. At the time of birth, all future eggs are in the prophase stage. At adolescence, anterior pituitary hormones cause the development of several follicles in an ovary. This results in the primary oocyte finishing the first meiotic division. The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell. This second cell is called a polar body and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm. See photo @jackwestin.com.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
The early stages of embryonic development begin with fertilization. Fertilization is the process in which haploid gametes (sperm and ovum) fuse to form a diploid cell called a zygote. To ensure that each zygote has the correct number of chromosomes, only one sperm can fuse with one egg. For fertilization to occur, sperm must be deposited in the vagina so that it can swim through the cervix and into the uterus, and then up into the fallopian tube where fertilization of the ovum happens. After fertilizing the developing cell that is now called an embryo, it repeatedly divides several times until a solid ball of cells called morula forms. As the cells in the morula continue to divide, they begin to move towards the outer edges of the ball, until it becomes a hollow ball of cells called the blastula.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth-Key Points
The ectoderm gives rise to the nervous system and the epidermal skin cells, the mesoderm gives rise to the muscle cells and connective tissue in the body, and the endoderm gives rise to columnar cells and internal organs. The embryo becomes the fetus that grows inside the uterus and further develops and continues until birth. The fetus depends on its mother for nourishment and oxygen. At birth, the first breaths of air, the lungs start to expand, and the lungs' ducts both close; the circulation and blood flow through the heart now function like an adult's.
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation
The formation of egg and sperm cells varies. Spermatogonium renews its population by mitosis throughout life while oogonium stops renewing its population sometime before birth. During meiosis, the primary and secondary oocytes arrest in prophase I and metaphase II, respectively, while primary and secondary spermatocytes directly go through meiotic cell division to produce haploid cells. Between the secondary spermatocyte and the sperm, there's the spermatid. After secondary oocyte, ovum develops. See photo @jackwestin.com.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
The next stage in embryonic development is the formation of the body plan. During gastrulation, the blastula undergoes a process called gastrulation, in which the three germ layers form, mainly, the ectoderm, mesoderm, and endoderm. The ectoderm gives rise to the nervous system and the epidermal skin cells, the mesoderm gives rise to the muscle cells and connective tissue in the body, and the endoderm gives rise to columnar cells and internal organs. See photo @jackwestin.com.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
The reproductive sequence of fertilization, implantation, development, and birth is the activity in which an organism develops from a single-celled zygote to a multi-cellular organism.
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth
Upon reaching the uterus, blastula embeds itself in the thickened endometrium (lining of the uterus) by the process called implantation. Once it implants itself in the uterine lining, pregnancy begins.
Reproductive system-Gametogenesis by meiosis-Key Terms
meiosis: cell division of a diploid cell into four haploid cells, which develop to produce gametes mitosis: the division of a cell nucleus in which the genome is copied and separated into two identical halves. It is normally followed by cell division polar body: one of the small cells that are by-products of the meiosis that forms an egg oocyte: a cell that develops into an egg or ovum; a female gametocyte
Reproductive system-Gametogenesis by meiosis-Key Terms
metaphase: chromosomes line up at the metaphase plate ovulation: the release of an egg during menstruation in females diploid: a full set of chromosomes, 46 in humans spermatogenesis: the process by which haploid spermatozoa develop from germ cells haploid: half the number of chromosomes
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation-Key Terms
mitosis: the division of a cell nucleus in which the genome is copied and separated into two identical halves. It is normally followed by cell division oocyte: a cell that develops into an egg or ovum; a female gametocyte oogonium: an immature female reproductive cell that gives rise to primary oocytes by mitosis spermatid: the haploid male gametid that results from the division of secondary spermatocytes spermiogenesis: the final stage of spermatogenesis, which sees the maturation of spermatids into mature spermatozoa spermatozoa: the mature motile male sex cell of an animal haploid: half the number of chromosomes
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth-Key Terms
ovum: the female reproductive cell morula: is an early-stage embryo consisting of 16 cells blastula: an animal embryo at the early stage of development when it is a hollow ball of cells gastrulation: single-layered blastula is reorganized into a multilayered structure known as the gastrula organogenesis: the process by which the three germ tissue layers of the embryo, which are the ectoderm, endoderm, and mesoderm, develop into the internal organs of the organism.
Reproductive system-Gametogenesis by meiosis-Key Terms
spermatocyte: a male gametocyte, from which a spermatozoon develops oogenesis: growth process in which the primary egg cell (or ovum) becomes a mature ovum oogonium: an immature female reproductive cell that gives rise to primary oocytes by mitosis prophase: the first phase of mitosis, the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation-Key Terms
spermatozoa: the mature motile male sex cell of an animal or human ovum: the female reproductive cell sperm: the male reproductive cell gametes: sex cells meiosis: cell division of a diploid cell into four haploid cells, which develop to produce gametes
Reproductive system-Reproductive sequence: fertilization, implantation, development, birth-Key Terms
zygote: a fertilized egg cell fertilization: The act of fecundating or impregnating animal or vegetable gametes implantation: The embedding of the fertilized ovum into the uterine wall fetus: an unborn offspring of a mammal umbilical cord: is a narrow tube-like structure that connects the developing baby to the placenta
Reproductive system-Ovum and Sperm/Differences in formation, Differences in morphology, and Relative contribution to next generation
Sperm and ovum also differ in characteristics. Spermatids undergo a morphological change, known as spermiogenesis, which then becomes spermatozoa. There is no corresponding stage observed in females. However, ovum, rounded-sphere, non-motile egg, is larger compared to the sperm cell. On the contrary, sperm cell, a motile flagellum, is differentiated into the head, neck, middle piece and tail and the smallest cell in the male body. The middle piece of the sperm contains many mitochondria, to generate ATP for motility.
Reproductive system-Gametogenesis by meiosis
Spermatogenesis occurs in the wall of the seminiferous tubules. Immediately under the capsule of the tubule are diploid, undifferentiated cells called spermatogonia (singular: spermatagonium), go through mitosis with one offspring growing into a sperm cell and the other progressing to the next generation of sperm.
Reproductive system-Gametogenesis by meiosis
Spermatogenesis. During spermatogenesis, four sperms result from each primary spermatocyte, which divides into two haploid secondary spermatocytes; these cells will go through a second meiotic division to produce four spermatids. See photo @jackwestin.com.
