The testicles are also part of the endocrine system because they make hormones , including testosterone tess-TOSS-tuh-rone. Testosterone is a major part of puberty in boys, and as a guy makes his way through puberty, his testicles produce more and more of it.
Testosterone is the hormone that causes boys to develop deeper voices , bigger muscles, and body and facial hair. It also stimulates the production of sperm. Alongside the testicles are the epididymis and the vas deferens, which transport sperm. The epididymis ep-uh-DID-uh-miss and the testicles hang in a pouch-like structure outside the pelvis called the scrotum.
This bag of skin helps to regulate the temperature of testicles, which need to be kept cooler than body temperature to produce sperm. The scrotum changes size to maintain the right temperature. When the body is cold, the scrotum shrinks and becomes tighter to hold in body heat.
When it's warm, it gets larger and floppier to get rid of extra heat. This happens without a guy ever having to think about it. The brain and the nervous system give the scrotum the cue to change size. The accessory glands , including the seminal vesicles and the prostate gland , provide fluids that lubricate the duct system and nourish the sperm. The urethra is the channel that carries the sperm in fluid called semen to the outside of the body through the penis.
The urethra is also part of the urinary system because it is also the channel through which pee passes as it leaves the bladder and exits the body. The penis is actually made up of two parts: the shaft and the glans. The shaft is the main part of the penis and the glans is the tip sometimes called the head. At the end of the glans is a small slit or opening, which is where semen and urine exit the body through the urethra yoo-REE-thruh.
The inside of the penis is made of a spongy tissue that can expand and contract. In the next substage, zygonema, there is further condensation of the chromosomes. As they come into closer contact, a protein compound called the synaptonemal complex forms between each pair of double-stranded chromosomes. As Prophase I continues into its next substage, pachynema, the homologous chromosomes move even closer to each other as the synaptonemal complex becomes more intricate and developed.
This process is called synapsis, and the synapsed chromosomes are called a tetrad. The tetrad is composed of four chromatids which make up the two homologous chromosomes.
During pachynema and the next substage, diplonema, certain regions of synapsed chromosomes often become closely associated and swap corresponding segments of the DNA in a process known as chiasma.
At this point, while still associated at the chiasmata, the sister chromatids start to part from each other although they are still firmly bound at the centromere; this creates the X-shape commonly associated with condensed chromosomes.
The nuclear membrane starts to dissolve by the end of diplonema and the chromosomes complete their condensation in preparation for the last substage of prophase I, diakinesis. During this part, the chiasmata terminalize move toward the ends of their respective chromatids and drift further apart, with each chromatid now bearing some newly-acquired genetic material as the result of crossing over.
Simultaneously, the centrioles, pairs of cylindrical microtubular organelles, move to opposite poles and the region containing them becomes the source for spindle fibers. These spindle fibers anchor onto the kinetochore, a macromolecule that regulates the interaction between them and the chromosome during the next stages of meiosis. The kinetochores are attached to the centromere of each chromosome and help move the chromosomes to position along a three-dimensional plane at the middle of the cell, called the metaphase plate.
The cell now prepares for metaphase I, the next step after prophase I. During metaphase I, the tetrads finish aligning along the metaphase plate, although the orientation of the chromosomes making them up is random. The chromosomes have fully condensed by the point and are firmly associated with the spindle fibers in preparation for the next step, anaphase I.
During this third stage of meiosis I, the tetrads are pulled apart by the spindle fibers, each half becoming a dyad in effect, a chromosome or two sister chromatids attached at the centromere. Assuming that nondisjunction failure of chromosomes to separate does not occur, half of the chromosomes in the cell will be maneuvered to one pole while the rest will be pulled to the opposite pole.
This migration of the chromosomes is followed by the final and brief step of meiosis I, telophase I, which, coupled with cytokinesis physical separation of the entire mother cell , produces two daughter cells. Each of these daughter cells contains 23 dyads, which sum up to 46 monads or single-stranded chromosomes. Meiosis II follows with no further replication of the genetic material.
The chromosomes briefly unravel at the end of meiosis I, and at the beginning of meiosis II they must reform into chromosomes in their newly-created cells. In contrast, each egg cell, or ovum, is relatively large and non-motile. During fertilization, a spermatozoon and ovum unite to form a new diploid organism. Further Exploration Concept Links for further exploration haploid principle of segregation principle of independent assortment meiosis chromosome diploid replication recombination principle of segregation principle of uniformity Principles of Inheritance.
Related Concepts You have authorized LearnCasting of your reading list in Scitable. While in anisogamy the two gametes are morphologically different and are known as male and female. The conventional theory believes that the origin of anisogamy is based on the fact that the highest number of positive fusion of gametes occurs when the gametic material accessible for the population has undergone division with a high degree of anisogamy.
It, therefore, assumes that a fixed quantity of the reserve material is essential for the zygote development and only disassortative fusions i. Thus, as per this theory, a large number of sperms are produced in the males to increase the fertilization probability.
Evidence suggests that fertility i. Hence, the higher the number of sperms in the semen, the higher is the chance of fertilization. This is also based on the fact that the higher number of sperms causes competition amongst the sperms for fertilization and therefore higher fertility.
Moreover, the function of the male sperm is to transfer the genetic material only, and a large number of sperms that are small in size provide an evolutionary advantage. While the ovum invests a huge amount of energy in creating a viable zygote than a male gamete.
In order to ensure a higher probability of survival, the egg contributes genetic material of its nucleus, mitochondrial genes , and provides essential nutrition for the initial development of the zygote. Thus, to provide all the necessary content, the ovum is large in size with a suitable amount of all the required content. This is thereby believed to have led to the development of anisogamy wherein eggs are non-motile, large in size and are limited in number whereas sperms are small, motile structures produced in large numbers.
The presence of an abnormal number of chromosomes is known as aneuploidy. A normal human cell contains 46 chromosomes. This abnormal chromosomal number results in genetic disbalance causing a disorder. This form of mutation is the second most common type of mutations. Aneuploidy is the result of non-separating chromosomes between two cells during cell division i.
Cases of aneuploidy in the germline cause miscarriage. A 46 XX is a normal female whereas46 XY is a normal male. The commonest form of aneuploidy is trisomy. Some known forms of aneuploidy are the following:. Thus, if these gametes become dysfunctional, the species may then have to deal with reduced propagation and species diversity. Both of these are crucial in the survivability of the species. In the sexual development of the malarial parasitic protozoans, Plasmodium spp.
See the figure below. Notice how the gametocytes develop into two types: the macrogamete female gamete and the microgamete male gamete. The male gamete eventually fertilizes the female gamete resulting in the formation of oocysts , which eventually develop into an ookinete.
However, the host immune factors act on these males and females throughout their sexual development and can render them dysfunctional.
A dysfunctional gamete can participate in the fertilization process, however, the fusion of a healthy gamete with dysfunctional gamete results in the formation of a nonviable zygote that does not survive to reach the ookinete stage. Try to answer the quiz below to check what you have learned so far about gametes.
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. Read this tutorial to know more about this form of inheritance 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.
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 This tutorial describes the independent assortment of chromosomes and crossing over as important events in meiosis. Read this tutorial to know more details in each of these meiotic events and how they promote genetic diversity in sexually-reproducing organisms This tutorial looks at sex determination via the sex chromosomes, X and Y.
Read it to get more info on X and Y chromosomes and the genetic traits inherited via these two Developmental Biology. Skip to content Main Navigation Search. Dictionary Articles Tutorials Biology Forum. Table of Contents. Gamete biology definition : a mature haploid reproductive cell as produced by gametogenesis , and that which fuses with another from the opposite sex at fertilization resulting in the formation of a zygote that develops into a new individual.
Synonyms: sex cell; reproductive cell. Sexual reproduction involving female and male gametes of different sizes is called anisogamy or heterogamy. Isogamy, in contrast, is a form of sexual reproduction wherein both male and female gametes are of the same size.
A gamete is a reproductive cell or sex cell that contains the haploid set of chromosomes. It is produced through a germ cell that undergoes gametogenesis , a process of gamete formation involving meiosis. The gametogenesis that leads to the production of the female gamete is called oogenesis.
The process of producing the male gamete is called spermatogenesis. In certain organisms , like humans, there are two morphologically distinct types of gametes: 1 the male gamete i.
0コメント