Genetics
The genetic code underlies the formation of the human body

Everything is Coded in your Dna



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The genetic code underlies the formation of the human body
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"Everything is Coded in your Dna"
Caption: The genetic code underlies the formation of the human body
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Image by: Jane Ades, National Human Genome Research Institute
© Public domain, Press photo gallery http://www.genome.gov/pressDisplay.cfm?photoID=39

Everything about the human body is determined by genetics, even one’s looks. Within each human cell is the genetic code in the form of DNA. DNA is basically made of four chemical components called nucleotides that occur in seemingly random sequences. Segments of sequence called genes encode specific proteins, which direct cell functions, act as hormones, and guide further DNA transcription and cell division.

There are a number of genes known to contribute to various aspects of human aesthetics, including height, weight, limb length, skin tone, eye color, hair color and texture, bone structure, and whether a person has freckles and wrinkles. This also means that all of these aspects are heritable – we get them from our parents.

Height is determined by the growth of the long bones prior to closure of the ends of the bones in the limbs, called the epiphyseal plate. This process is guided by somatotropin, or growth hormone, a protein secreted by the pituitary gland that induces another protein to be secreted by the liver. The process also involves receptors, which are encoded by other genes. Moreover, researchers have identified an association of the gene known as HMGA2 with a person being tall vs. short (BBC). This makes height a multigenic (multiple genes) characteristic.

The height process also influences limb length because of the involvement of the long bones. However, the stability of the limbs also hinges on connective tissues. Genetic diseases that compromise the connective tissues sometimes manifest as awkwardly long limbs and extremities (sometimes called “gangly”), such as Marfan’s Syndrome. Many studies to determine the genes involved in limb growth and length have focused on the occurrence of stubby limbs in mice and dogs. Growth factors are involved at early stages of development, and they also determine limb patterning – the symmetric top arms, bottom legs, one on each side- seen in mammals.

In a similar manner, genes affect bone structure in general. Studies have shown that humans conceive symmetry as beauty. The symmetry of the skull and face depends on the underlying bone structure, and even cartilage growth and connective tissue. This makes “beauty” genetic. A number of genes are involved in this process, including collagen genes, genes that control the deposition and absorption of calcium and phosphorus, genes involved with vitamin D, and even transcription factors (e.g., TNFRSF1B) and transport proteins, such as low density lipoprotein receptor-related protein (LRP5). Diseases such as osteogenesis imperfecta have shown researchers how much the body’s structure relies on genetics.

Skin tone is determined by the skin’s production of melanin by melanocytes. Several genes appear to control this process, including some linked to hair color and whether a person has freckles. Much of the color spectrum known to vary among individuals are just variations of the same genes. Each gene has two copies in each person – called alleles. For recessive appearance characteristics, two of the same copies are needed; for dominant features, only one copy is needed. Red hair and freckles, which is coupled with pale skin and sun sensitivity, has been linked to recessive alleles of the genes MC1R and ASIP (NewScientist). OCA2 appears to take part in melanin production and has been linked to albinism, a recessive condition in which an individual lacks pigmentation of the hair, eyes, and skin.

Less evident factors of one’s looks are also affected by genetics, including weight, the appearance of wrinkles, and graying hair.

Weight is a combined measure of both bone structure and the mass, both muscle and fat, of a human body. Muscle mass is affected by several genes, including myostatin. Some of these genes are investigated in muscle weakness or wasting disorders, such as muscle dystrophy. Fat mass is influenced by genes that direct the storage of ingested fatty acids, including cholesterol transport and synthesis, as well as neurexin-3 (NRXN3), which is associated with the accumulation of fatty tissue around the abdomen.

How well melanocytes are maintained with age depends on genes, meaning that when hair goes gray is determined by genetics as well. The Bcl2 gene has been implicated in this process in mice (MSNBC). Also part of the aging process, wrinkles are determined by our parents – up to 1500 genes are implicated in maintaining wrinkle-free skin with age. Most to blame are genes that encode proteins to deal with free radicals. Reducing environmental exposure to these compounds can counter a lack of genetic safeguards (NYDailyNews), unlike the purely genetic aspects like height.

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