Sex Determination Simplified Essay Example

cells based on weight. The white blood cells or leucocytes are collected after spinning and put into a culture medium where they are incubated in a warm environment for 72 hours (Guo and Thompson, 1992).

The culture medium utilized for culturing leucocytes includes glucose as the energy source, essential amino acids, and minerals to support their growth. Additionally, phytohaemagglutinin is introduced to stimulate cell division and re-enter the cell cycle. Scientists typically observe metaphase chromosomes aligning in the equatorial plate of the cell, preparing to split into two chromatids and move towards opposite poles. This separation mechanism readies the chromosomes before the cell divides to form two daughter cells.

When the dividing cells of the cell cycle reach the metaphase stage, the blood cultures are processed further after 72 hours and spun down to remove the culture medium. Subsequently, the cells settle at the bottom of the test tube and are resuspended in a hypotonic solution, which causes them to swell in preparation for karyotyping. The swollen cells are then fixed with a preservative solution and applied onto glass slides for microscopic examination. The cytogenetic technologist, who specializes in the preparation and interpretation of chromosome slides, analyzes all 46 chromosomes present in each cell.

An individual's sex chromosomes are typically either XX for females or XY for males, but there are cases where aneuploidy occurs resulting in more than two sex chromosomes. This condition is characterized by a numerical abnormality due to the presence of additional chromosomes in each cell and is known as trisomy when three sex chromosomes are present (Jurmain et al., 2007).

Klinefelter syndrome is a type of trisomy characterized by a person having

XXY sex chromosomes. Individuals with this syndrome exhibit both male and female sex traits, including breasts and testes. They tend to be tall and thin and frequently experience mental disabilities. Furthermore, individuals with Klinefelter syndrome lose their fertility.

Trisomy X or XXX is another form of trisomy that is sometimes called superfemale. Despite the name, these individuals may not necessarily exhibit exaggerated female traits like larger breasts or a more attractive face. Rather, superfemale refers to having three X chromosomes instead of the typical two required for femaleness. Despite displaying normal female physical features, those with this condition may be sterile and have intellectual disabilities.

Turner's syndrome causes individuals to experience various symptoms, including short stature, webbed necks, mental retardation, and social relationship difficulties. This is due to a deficiency in sex chromosomes resulting in only one X chromosome. The development of human sex relies on primary sex characteristics such as ovaries and testes, while hormones are essential for controlling the existence and concentration of gender-specific hormones.

Hormones are proteins secreted by specific organs in the body. While some hormones are produced equally by both genders, others are unique to either males or females. Females have estrogen which plays a crucial role in regulating their monthly menstrual cycle. Another female-specific hormone is progesterone, also known as the pregnancy hormone, that increases during pregnancy and contributes to thickening of the uterus for nourishing and protecting the developing fetus.

According to McLaren (1988), in the early stages of pregnancy, the fetus is gender-neutral and consists of basic tissues found in both male and female fetuses. A theory from fifty years ago suggests that all fetuses are initially predetermined to develop into

females due to the presence of female hormones such as estrogen and progesterone. Nevertheless, during the sixth week of gestation, testosterone is generated, which counteracts the effects of these female hormones. Consequently, male-specific testes form from primitive sexual organs when testosterone suppresses estrogen and progesterone.

During fetal development, the growth of ovaries is prompted by estrogen and progesterone when testosterone is absent, resulting in female fetus formation. Conversely, seminal vesicles, epididymis, and vas deferens are facilitated via the growth of Wolffian ducts with testosterone. The scrotum and penis - male-specific external genitalia - are developed through dihydrotestosterone's conversion by urogenital tubercle cells. Additionally, Mullerian inhibiting substance produced by Sertoli cells prompts self-destruction of Mullerian ducts.

In the absence of certain proteins, the Wolffian ducts degenerate and the Mullerian ducts transform into the oviducts, uterus, cervix, and upper vagina. In males, the SRY gene is associated with the formation of testes in a developing fetus. The SRY protein suppresses other sex-specific hormones, allowing only testosterone to be produced and leading to the development of male-specific organs like the testes. Another pathway for determining sex in humans is through the development of secondary sexual characteristics, controlled by specific hormones.

The localization of TDF to a 35-kb region on the short arm of the Y chromosome was investigated through linking deletions on the Y with the presence or absence of testes and studying XX males who carry a small portion of the Y on one of their X chromosomes. The cloning of this region led to the identification of the sex-determining region Y (SRY) gene by Koopman et al. in 1991. The evidence for SRY being the testis-determining gene was obtained

through transgenic experiments, where it was shown that a 14.6-kb genomic sequence of the mouse SRY locus has the capability of inducing XX fetuses to develop into males.

The SRY gene is believed to be instrumental in converting fetal gonads into testes by activating various gene interactions. SRY belongs to the HMG protein family, which uses an 80-amino acid DNA-binding sequence called the HMG domain to regulate transcription by binding to specific DNA sequences. One such protein in this family is SRY, which has a target sequence found in the promoter region of certain genes involved in differentiation, including Mullerian inhibiting substance and P450 aromatase - an enzyme responsible for converting testosterone to estradiol. Interestingly, this same target sequence can also be found in the promoter region of the SRY gene itself, creating a positive feedback loop. It took over thirty years from first discovering that sex was determined by the Y chromosome until identifying SRY as the TDF.

Discovering the SRY gene was a major step forward in understanding human sex determination. The next task is to decipher how SRY controls transcription and influences nearby genes connected to the sex determination pathway.

contrasting mitosis and meiosis