X chromosome in the context of "Men"

Sex is the biological trait that determines whether an anisogamous sexually reproducing organism produces male or female gametes. During sexual reproduction, a male and a female gamete fuse to form a zygote, which develops into an offspring that inherits traits from each parent. By convention, organisms that produce smaller gametes (spermatozoa, sperm) are called male, while organisms that produce larger gametes (ova, often called egg cells) are called female. An organism that produces both types of gamete is a hermaphrodite.

In non-hermaphroditic species, the sex of an individual is determined through one of several biological sex-determination systems. Most mammalian species have the XY sex-determination system, where the male usually carries an X and a Y chromosome (XY), and the female usually carries two X chromosomes (XX). Other chromosomal sex-determination systems in animals include the ZW system in birds, and the XO system in some insects. Various environmental systems include temperature-dependent sex determination in reptiles and crustaceans.

A man is an adult male human. Before adulthood, a male child or adolescent is referred to as a boy.

Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chromosome from the father. Sex differentiation of the male fetus is governed by the SRY gene on the Y chromosome. During puberty, hormones which stimulate androgen production result in the development of secondary sexual characteristics that result in even more differences between the sexes. These include greater muscle mass, greater height, the growth of facial hair and a lower body fat composition. Male anatomy is distinguished from female anatomy by the male reproductive system, which includes the testicles, sperm ducts, prostate gland and epididymides, and penis. Secondary sex characteristics include a narrower pelvis and hips, and smaller breasts and nipples.

A woman is an adult female human. Before adulthood, a female child or adolescent is referred to as a girl.

Typically, women inherit a pair of X chromosomes, one from each parent. Sex differentiation of the female fetus is governed by the lack of a present functioning SRY gene on either one of the respective sex chromosomes. Female anatomy is distinguished from male anatomy by the female reproductive system, which includes the ovaries, fallopian tubes, uterus, vagina, and vulva. A woman generally has a wider pelvis, broader hips, and larger breasts than a man. These characteristics can facilitate pregnancy, childbirth and breastfeeding. Women typically have less facial and other body hair, have a higher body fat composition, and are on average shorter and less muscular than men. Women are at greater risk of certain diseases like breast cancer, and at lower risk of other diseases like lung cancer.

A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosome abnormality. Although polygenic disorders are the most common, the term is mostly used when discussing disorders with a single genetic cause, either in a gene or chromosome. The mutation responsible can occur spontaneously before embryonic development (a de novo mutation), or it can be inherited from two parents who are carriers of a faulty gene (autosomal recessive inheritance) or from a parent with the disorder (autosomal dominant inheritance). When the genetic disorder is inherited from one or both parents, it is also classified as a hereditary disease. Some disorders are caused by a mutation on the X chromosome and have X-linked inheritance. Very few disorders are inherited on the Y chromosome or mitochondrial DNA (due to their size).

There are well over 6,000 known genetic disorders, and new genetic disorders are constantly being described in medical literature. More than 600 genetic disorders are treatable. Around 1 in 50 people are affected by a known single-gene disorder, while around 1 in 263 are affected by a chromosomal disorder. Around 65% of people have some kind of health problem as a result of congenital genetic mutations. Due to the significantly large number of genetic disorders, approximately 1 in 21 people are affected by a genetic disorder classified as "rare" (usually defined as affecting less than 1 in 2,000 people). Most genetic disorders are rare in themselves.

Lesch–Nyhan syndrome (LNS) is a rare inherited disorder caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRT). This deficiency occurs due to mutations in the HPRT1 gene located on the X chromosome. LNS affects about 1 in 380,000 live births. The disorder was first recognized and clinically characterized by American medical student Michael Lesch and his mentor, pediatrician William Nyhan, at Johns Hopkins.

The HGPRT deficiency causes a build-up of uric acid in all body fluids. The combination of increased synthesis and decreased utilization of purines leads to high levels of uric acid production. This results in both high levels of uric acid in the blood and urine, associated with severe gout and kidney problems. Neurological signs include poor muscle control and moderate intellectual disability. These complications usually appear in the first year of life. Beginning in the second year of life, a particularly striking feature of LNS is self-mutilating behaviors, characterized by lip and finger biting. Neurological symptoms include facial grimacing, involuntary writhing, and repetitive movements of the arms and legs similar to those seen in Huntington's disease. The cause of the neurological abnormalities remains unknown. Because a lack of HGPRT causes the body to poorly utilize vitamin B₁₂, some males may develop megaloblastic anemia.

The XY sex-determination system is a sex-determination system present in many mammals (including humans), some insects (Drosophila), some snakes, some fish (guppies), and some plants (Ginkgo tree).

In this system, the karyotypic sex of an individual is usually determined by a pair of sex chromosomes. Typically, karyotypic females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Karyotypic males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex. In humans, the presence of the Y chromosome is responsible for triggering male phenotypic development; in the absence of the Y chromosome, the individual will usually develop phenotypicaly female. In most species with XY sex determination, an organism must have at least one X chromosome in order to survive.