Introduction

Human reproduction is any form of sexual reproduction which results in one or more viable offspring. Sexual reproduction is the use of two beings’, usually the same species though not always, genetic material to create a new being, also usually of the same species. As of yet, humans have not been able to reproduce asexually. Asexual reproduction only requires DNA from one being to create offspring. This is common amongst Prokaryotes, as well as some plants, fungi, and even animals as the primary method of reproduction.

Sexual intercourse between a man and a woman is the most common form of sexual reproduction in humans. However, there are other forms, such as in vitro fertilization and artificial insemination, which are able to result in healthy offspring. Sexual intercourse requires the interaction of the female and male reproductive systems to fertilize the female egg by the male’s sperm. Other human forms of sexual reproduction do not require the interaction of the male and female reproductive systems. Instead, a third party will orchestrate the fertilization either completely or partially outside the human body. For instance, the female egg may be fertilized with sperm inside a petri dish before being implanted in the female’s body, or the sperm may be introduced to the egg inside the human body by the use of a special machine. No matter the technique used, if the egg is fertilized gestation will begin.

Gestation is the time period that begins at conception, or the moment the female egg is fertilized, and continues until either the termination or successful birth of the offspring. This is also known as a pregnancy. Termination of a pregnancy can either be voluntary, and carried out by a process known as abortion, or involuntary. An involuntary termination is known as a miscarriage and can occur at any point during the gestation period. However, if the fetus miscarries late in the pregnancy, the mother may have to perform what is known as a still birth. Most magical pregnancies which continue after the first term result in healthy offspring. The process of reproduction may involve many steps and appear complex, but it can easily be understood when broken down to each step in the process.

Meiosis

Before the male and female sex cells can combine to make a new being, they must be produced by the process of meiosis. In regular cell division a parent cell undergoes the process of mitosis to create two daughter cells which are identical to the parent cell. This allows for the growth and repair of tissues, fibers, and membranes and is also how single-celled organisms reproduce. Mitosis is another name for asexual reproduction and occurs in all organisms.

The original cell undergoes division once in mitosis. This can be broken down into four steps for humans: prophase, metaphase, anaphase, and telophase. During prophase the nuclear membrane dissolves. The chromatin tightly coils and condenses during Interphase until it forms chromosomes. Chromosomes are composed of two identical chromatids that are joined together by the centromere. The chromosomes align along the middle of the cell during metaphase and are pulled apart by the centrosomes during anaphase. The centrosomes move away from the nucleus, leaving behind a spindle apparatus which then will separate the chromosomes and pull them towards the centrosomes when the spindles shorten. During telophase the spindle apparatus dissolves, nuclear membranes form around the separated chromosomes, and the chromosomes then begin to uncoil and return to their chromatin state. Though not a step of mitosis, the end of mitosis is marked by the process of cytokinesis, which separates the two daughter cells completely into two new, unique cells. The cells will be identical due to the mitotic process.

In meiosis, however, the daughter cells produced are not identical. This process has two division phases known as meiosis 1 and meiosis 2. Each of these stages has its own prophase, metaphase, anaphase, and telophase.

During prophase 1 the nuclear membrane dissolves, chromosomes form, centrosomes push apart, and the spindle apparatus appears, just like in mitosis. However, homologous chromosomes also begin to pair up and exchange DNA. This exchange is known as crossing over and is essential for genetic diversity. During metaphase 1 The chromosomes will align along the center of the cell. During anaphase 1, half the pairs of chromosomes will go to one side of the cell and the other pairs to the other side. The chromosomes are not yet pulled apart to their original chromatids, unlike during mitosis. Cytokinesis will begin after this stage and before the beginning of telophase 1 to separate the two daughter cells. Telophase 1 includes the forming of nuclear membranes around the chromosomes as well as the dissolving of the spindle apparatus.

In prophase 2 the centrosomes of the two daughter cells will form and start to split the new cells. The nuclear membranes will dissolve and the spindle apparatus will develop. In metaphase 2 the spindle fibers connect to the centromeres and the chromosomes will align along the center of the cell. During anaphase 2 the chromosomes finally separate to the chromatids and are pulled by the spindle fibers to opposite ends of the cell. Cytokinesis aids telophase 2 in splitting the cells and nuclear membranes form around the chromatids.

The entire process of meiosis results in four haploid cells, or cells with half the DNA of regular cells. These cells are called gametes and are now considered sex cells. Sexual reproduction could not occur successfully without the use of these gametes.

The Male Reproductive System

The male reproductive system can be divided into two main parts which can be categorized as production/storage and distribution centers. The scrotum and testes is the production center of the male gamete, or male sex cell, known as sperm. The scrotum itself is a pouch-like structure which hangs behind the penis and contains and protects the testes. It contains numerous nerves and blood vessels as well as muscles. The Cremaster muscle contracts to pull the scrotum closer to the body when it is cold and the Dartos muscle gives it a wrinkled appearance. When temperature increases, these two muscles relax so the scrotum will appear smoother and hang lower. The scrotum is connected to the abdomen by the inguinal canal. This canal contains the spermatic cord which is composed of the spermatic artery, vein, and nerve bound together by connective tissue. The spermatic cord passes into the testis.

The testes lie inside the scrotum and outside of the abdominal cavity by design. Sperm is produced by the testes. Sperm is unable to survive at the average internal body temperature of 37 degrees Celsius. At this temperature sperm can undergo many negative side effects, including spontaneous mutation, which can lead to detrimental disorders in offspring. The optimal temperature for sperm is approximately 2-3 degrees cooler than the internal body temperature, making an external pouch to house the testes essential. The contraction and relaxation of the scrotal muscles further helps to maintain the health of sperm.

Once produced, sperm is stored in the epididymis. This is also where sperm will mature until they are ready to fertilize an egg. The epididymis is a mass of tightly coiled tubes which lies against the testicles. Sperm moves from the epididymis to the pelvic cavity by way of the vas deferens, or sperm duct. This tube is approximately 30 centimeters long.

The distribution center of the male reproductive system is the penis. The penis is an external organ which functions to release, or ejaculate, sperm in the reproductive system. It is the male copulatory organ and has a long shaft topped by an enlarged bulbous tip. This tip is called the glans penis, which supports and is protected by the foreskin (in uncircumcised individuals). During sexual arousal sinuses within the erectile tissue of the penis fill with blood, causing the penis to become erect and ready for sexual activity. Blood flows into the erectile cartilage under pressure because of the veins of the penis are passively compressed and the arteries are dilated. The penis also expels urine from the body for the excretory system. Though the female body separates these two systems, the male body utilizes the urethra, which is contained in the penis, for both.

There are also three accessory glands which are used by this system to lubricate the ducts and provide nourishment for the male gametes. These glands include the seminal vesicles, prostate, and Cowper’s glands. Seminal vesicles produce a sticky fluid which contains fructose. This fluid provides energy for sperm and aids their motility. Approximately 70% of semen is this fructose-rich fluid. Though sperm are the male gametes, semen is composed of sperm as well as fluids produced by the accessory glands to aid sperm in its journey to the female gamete. The seminal vesicles are sac-like structures which are attached to the vas deferens on one side of the bladder.

The prostate gland can be found just below the bladder, surrounding the ejaculatory ducts at the base of the urethra. This gland adds prostate fluid to the mixture of sperm cells and seminal fluid. At this point, the semen is called “proof semen”. The prostate also adds calcium to the mixture, giving semen its milky appearance. Prior to the addition of calcium, semen appears yellow due to the fructose in the seminal fluid. The prostate is the most well-known of the three accessory glands.

The final accessory gland serves a slightly different function than the other two accessory glands. The bulbourethral glands, or Cowper’s glands, are located on either side of the urethra below the prostate. These pea-sized glands are responsible for producing a clear fluid which empties directly into the urethra. The slippery fluid lubricates and neutralizes the urethra. Sperm will break down in acidic environments so this fluid is necessary if any acidity remains in the urethra due to residual urine.

There have been many theories regarding magical semen. Most recently, magical scientists postulated that magical sperm would move faster than non-magical sperm. They also believed that the magic present would make the sperm impervious to morphological changes due to heat or other environmental factors. Once tested, however, no such advantages were found in magical sperm. In fact, had this theory proven true, it should have led to higher rates of magical children in the world than what our current distribution patterns show.

Magical scientists were able to take semen samples from over 100 research subjects in 2012 to test the belief that magical sperm would be faster than non-magical sperm. The scientists suggested that magical sperm would need to be less dense to move faster than non-magical sperm. The scientists used a centrifuge, which was able to separate the sperm by weight, and found that there was no dominance of magical sperm in the less dense group. Furthermore, there was no sign that density was controlled by the presence of magic in the sperm. They were able to confirm the findings of non-magical scientists that less dense sperm predominantly contains the y chromosome while denser sperm contained the x chromosome. Further tests disproved the hypothesis that magical sperm would still move faster.

The current predominant theory is that, though sperm which contains the magical gene can be detected, this gene is not active until fertilization of the female gamete. Therefore, the sperm containing the magical gene was afforded no extra protection or advantages than sperm which did not contain the gene.

The Female Reproductive System

Much like the male reproductive system, the female reproductive system can be divided into two main parts. These parts can be considered the production and reception centers. The female reproductive organs are all internal, unlike the male reproductive organs, however, there are external structures which are considered part of female genitalia which function to protect the internal structures. The external structures are the mons pubis, labia majora and minora, pudendal cleft, clitoris, and Bartholin’s glands. The internal reproductive organs are the vagina, uterus, uterine tubes, and ovaries.

The vagina, or birth canal, is a tubular tract that leads from the body’s exterior to the uterus. It is a fibro-muscular structure which also serves as the canal which joins the cervix to the outside of the body. The vagina is also where sperm is deposited during ejaculation in sexual intercourse. The cervix, or neck of the uterus, is the lowest portion of the uterus. This structure is conically shaped and protrudes through the upper vaginal wall anteriorly. Approximately half of the cervix is visible to the naked eye when viewed vaginally, while the remainder lies above the vagina and out of view.

The uterus, also called the womb, is the major female reproductive organ in humans. It functions as mechanical protection, nutritional support, and waste remover for developing embryos and fetuses. Contractions in the wall of the uterus also function to push out the fetus during the birthing process. The major function of this pear-shaped organ is to accept a fertilized ovum, or egg, which will then be implanted in the endometrium and receive nourishment from blood vessels. A fertilized ovum will develop into an embryo before becoming a fetus until birth. However, if a fertilized egg does not embed in the uterine wall, menstruation will occur.

The ovum reaches the uterus by way of the Fallopian tubes. There are two Fallopian tubes, also called oviducts, which lead from the ovaries into the uterus. When an ovum matures in the ovary, the follicle and ovary wall rupture, releasing the ovum, which then is able to enter the Fallopian tube. The ovum can take hours or days to travel through the Fallopian tube, pushed along by cilia which lines the inner tubes. Fertilization of an ovum usually occurs in the Fallopian tube, normally in the ampullary-isthimic junction. If the ovum is fertilized, it will implant in the endometrium and pregnancy will begin.

The ovaries are paired organs located in the pelvic cavity near the lateral walls. These small organs are responsible for producing ova and secreting hormones. Once an ovum is produced and matured it is released in a process called ovulation. The frequency and timing of ovulation is periodic and directly impacts the length of a woman’s menstrual cycle. The ovaries will release an ovum once a month on average in fertile human females. Ova are much larger than sperm because, unlike sperm, ova contain all the nutrients the fertilized egg will need for the initial stages of gestation, in addition to the mother’s half of the genes. Unlike the meiotic process which produces sperm, only one of the four gametes produced in the female meiotic process will mature. The other three are usually used as nutrients for the fourth. This process is known as oogenesis. These gametes are also produced in the female fetus prior to birth. Therefore, a female is born with her entire ova supply and produces no more while males are able to produce sperm for most of their lives.

There have been less hypotheses made about magical ovum, though there are a few which have entered the scientific community. One hypothesis was the magical ovum would be resistant to non-magical sperm. This led to the belief that truly magical women would be unable to become pregnant with non-magical offspring. This thought produced a negative stigma towards witches with non-magical children for years, until research conclusively proved this idea to be false. In addition, many children have recently been the result of a union between one magical and one non-magical parent, so the theory that magical women would produce only magical children can not possibly be true. Scientists were able to conclude that, just in the case of magical sperm, an ovum carrying the magical gene does not have the ability to utilize that gene prior to fertilization.

Research into the reproductive process is at an all time high in the magical community. Many hypotheses are being tested and, though it is clear we may not have new pivotal information for many years, it is an exciting time to be working in the field. Many small discoveries are being made every day, leading to an expansion of the field and an influx of scientists within the magical community.

Next Chapter: Cell Biology