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Life begins the minute one egg and one sperm unite at conception. Over the past century technological advancements in science have allowed humanity to take a closer look into our younger selves; specifically, the process of our development well before birth. During sexual intercourse, millions upon millions of sperm are ejaculated into the vagina, a few will enter the cervix, less will pass through the cervix, even less will find the fallopian tubes, only a bit will reach the egg, and ultimately, only one will fertilize the ovum (Parker). Once the window of fertilization is over and the egg and the sperm have successfully fused, the developing human begins its embryotic development, where it will spend the next eight weeks forming its major organs as well as other structures needed in order to sustain life. As beautiful and exciting as this process may be, unfortunately it can result in a number of complications once the baby is born. For example, Trisomy 21 may occur due to nondisjunction, an error in cell division, resulting in an extra copy of chromosome 21, which will affect the baby for the rest of its life (Ambreen).
The fertilization process begins with a male sperm and a female ovum. The male sperm is made up of male sex cells, it is stored in the testes as it needs to be kept cool in order to avoid higher temperatures resulting in infertility and its structure consists of a head, a body, and a tail. The head includes a cap and a nucleus, where the genetic material, commonly known as DNA, is stored, the body contains the mitochondria, where the sperms energy comes from, and the tail provides swim-like mobility as it contracts and relaxes (Rice). On the other hand, the ovum is the female sex cells. A female is born with all the ova she will have in her lifetime, the ova is stored in the ovarian follicles located in the ovaries, and around age 12-15 her ova will begin maturing and releasing once a month, developing the corpus luteum which thickens the uterus wall, preparing it for an egg (Rice).
The ovum itself is a large cell, containing an external cell membrane full of protein as well as a nucleus which stores the female’s genetic material. Once the sperm and the ovum meet they will fuse, this is known as fertilization; this may only occur during ovulation, a very short window of opportunity of approximately 2-3 days where an egg is released, and the sperm must rapidly reach the vagina or else it will die (Irving). Following ovulation, the egg will be scooped up by the fallopian tube from which it was released from, and the sperm will have to swim through the cervix, past the uterus, finally meeting the ovum in the fallopian tube (Parker). To complete the fertilization process, the sperm will have to enter the ovum’s cell membrane and deposit its DNA, resulting in a now fertilized ovum, otherwise known as a zygote (Rice), containing 23 pairs of chromosomes, equally distributed from the mother and father.
The short period from fertilization till the eight weeks of pregnancy is where the developing human is considered an embryo. During the beginning phases of embryotic development, the process of cell division occurs, the zygote continues dividing in order to form the morula, a solid ball of cells, that will eventually become the blastocyst (Vitiella). About a week following fertilization implantation occurs, during this period a pregnancy hormone called hCG is released in the woman’s body, this is the hormone detected by pregnancy tests, taking approximately three to four weeks to identify (Parker).
Eventually, the blastocyst will become the embryo itself and embryonic discs will begin to form. In the first month, these discs are formed by the floor of the amniotic cavity which ultimately develop into the amniotic sac, and the placenta, a fluid filled sac around the embryo, its main purpose being the transport of nutrients to the embryo and the development of the three primary germ layers – the ectoderm, mesoderm, and endoderm, which will set the blueprint for the rest of the bodies structure (Vitiella). As the embryo’s development progresses, tissues and organs begin to form, starting with the brain and head, moving on to the body and arms, and ending at the legs, including the rest of the lower body (Irving). Eight weeks after fertilization (the end of the embryonic stage), all major body parts and organs will have formed, and facial features continue developing (Salamonsen).
Caused by an extra copy of chromosome 21, trisomy 21 is commonly referred to as Down Syndrome. This genetic disorder is caused by an error in cell division. A normal baby will have a complete set of 46 chromosomes, 23 from the mother and 23 from the father; Trisomy 21 will occur when an egg or sperm cell makes an extra copy of chromosome number 21, resulting in the fertilized egg passing on three copies of chromosome 21 (Ambreen). Occasionally, the extra chromosome 21 may attach to either the egg or the sperm, causing “translocation Down Syndrome”, the only form of Down Syndrome that can be inherited from a parent. Rarely, an error in cell division may occur after fertilization, with some cells being affected while others remain unharmed, this is known as “mosaic Down Syndrome” (Ambreen).
Overall, those affected by Trisomy 21 collectively share similar intellectual and physical traits; they suffer from learning and development delays which may affect their speech, intelligence, and social skills (Starbuck). In addition, those inflicted by Down Syndrome possess distinct facial features such as slanted eyes, flattened noses, poor muscle stone, short necks, and an overall small head including the eyes, mouth, and ears (Starbuck). Not to mention, the numerous health complications that come with Down Syndrome, for instance, respiratory, cardiovascular, and hearing issues may arise and while those conditions may be treated, there is no cure or prevention for down syndrome. On the upside, with today’s technological advancements Trisomy 21 can be detected before birth by analyzing the cells in the mother amniotic fluid or placenta through a noninvasive procedure (Ambreen).
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