Alcohol flush reaction is a condition in which an individual's face or body experiences flushes or blotches as a result of an accumulation of acetaldehyde, a byproduct of the catabolic metabolism of alcohol.

This reaction is usually experienced by people of East Asian descent - according to the analysis by HapMap project the allele of the ALDH2 gene responsible for this reaction is rare among Europeans and Africans, very rare among Mexican-Americans but quite common among people of Chinese and Japanese ancestry.

Not all humans have the same perception of bitterness - a genetic variation in TAS2R38 gene prevents some people from tasting propylthiouracil (PROP) - a compound often found in cabbage, raw broccoli, coffee and dark beers. About 25% of people lack ability to detect this compound due to gene mutations and they find most food and drink to be less bitter, or not bitter at all.

Some people have earwax that is wet, sticky and yellow or brown; other people's earwax is dry, crumbly and grayish.

The type of earwax is determined by a variation at a single gene (ATP-binding cassette C11 gene), with the 'wet earwax' allele being dominant over the 'dry earwax' one.

Lactose intolerance is the inability to digest lactose, a sugar found in milk and in some milk-derived dairy products.

Lactose intolerant individuals have insufficient levels of lactase, the enzyme that metabolizes lactose into glucose and galactose, in their digestive system. This condition is quite common in adults and is not dangerous, but has unpleasant symptomes such as abdominal bloating and cramps, flatulence, diarrhea or nausea after consuming significant amounts of dairy products.

The pigmentation of the iris in humans varies from light brown to black, depending on the concentration of melanin in the iris pigment epithelium (located on the back of the iris). In conjunction with white collagen fibers it produces different shades of grey, green and hazel.

Eye color is an inherited polygenic trait, influenced by more than one gene - there is evidence that as many as 16 different genes could be responsible for eye color in humans - yet studies show that it is possible to predict eye color with enough accuracy by using only 6 SNPs.

Hair color is determined by the amount of two pigments - brown-black eumelanin predominates in black and brown hair and red-yellow pheomelanin in red hair. Blond hair contains low levels of both pigments.

The genetics of human hair color are not firmly established yet, but there are indications that multiple genes determine whether a person will have brown, blond or red hair.

Breast size is moderately heritable and recent studies has identified a number of single-nucleotide polymorphisms (SNPs) significantly associated with breast size. These studies provide insight into the genetic factors underlying normal breast development and show that some of these factors are also shared with probability of having breast cancer.

Cleft lip and cleft palate are variations of a type of clefting congenital deformity caused by abnormal facial development. Approximately 1 in 700 children born have a cleft lip and/or a cleft palate.

Cleft lip is formed in the top of the lip as either a small gap or it continues into the nose. Cleft palate is a condition in which the two plates of the skull that form the hard palate are not completely joined.

Male Pattern Baldness is the most common cause of hair loss in men. In classic pattern baldness, hair is lost in a well-defined pattern, beginning above both temples. Hair also thins at the crown of the head. Often a rim of hair around the sides and rear of the head is left.

Alopecia Areata is a medical condition in which hair is lost from some or all areas of the body, usually from the scalp. It causes bald spots on the scalp, especially in the first stages. In some cases, the condition can spread to the entire scalp or to the entire epidermis.

Freckles are clusters of concentrated melaninized cells which are most easily visible on people with a fair complexion. The formation of freckles is triggered by exposure to sunlight - the exposure to UV-B radiation activates melanocytes to increase melanin production, which causes freckles to become darker and more visible. Although freckles are usually found on the face, they may also appear on any skin exposed to the sun, such as arms or shoulders.

Acne vulgaris (acne) is a common inflammatory skin disorder that occurs when hair follicles are clogged with dead skin cells and oil from the skin. Acne is characterized by areas of blackheads, whiteheads, pimples, and greasy skin, and may result in scarring. Genetics is thought to be the cause in about 80% of cases, while the remaining 20% are attributed to health, lifestyle and environment factors.

Prominent, or protruding ears are an inherited problem affecting 1-2% of the population. Prominent ears do not tend to improve and about 30% of babies who have prominent ears are born with normal-looking ears with the problem only arising in the first three months of life. There are no functional problems associated with prominent ears, but they may cause considerable psychological distress.

Most humans have ear lobes detached, but in some cases the lower lobe is connected to the side of the face.

The ABO system is the most important blood-group system in human blood transfusion.

ABO types are classified by presense and absense of associated anti-A and anti-B antibodies. Presense of these antibodies is encoded by one genetic locus, the ABO locus, which has three alternative forms:A, B, and O. A child receives one of the three variants from each parent, giving rise to six possible genotypes and four possible blood types.

High-density lipoprotein (HDL, "Good Cholesterol") is one of the five major groups of lipoproteins that enable lipids like cholesterol and triglycerides to be transported within the water-based bloodstream. In healthy individuals, about thirty percent of blood cholesterol is carried by HDL.

HDL particles are able to remove cholesterol from within artery atheroma and transport it back to the liver for excretion or re-utilization. People with higher levels of HDL seem to have fewer problems with cardiovascular diseases, while those with low HDL cholesterol levels have increased rates for heart disease.

Low-density lipoprotein (LDL, "Bad Cholesterol") is one of the five major groups of lipoproteins that enable lipids like cholesterol and triglycerides to be transported within the water-based bloodstream.

Studies have shown that higher levels of type LDL particles correlate with much faster growth of atheroma, progression of atherosclerosis and earlier and more severe cardiovascular disease events.

Cholesterol is an organic chemical substance classified as a waxy steroid of fat. Although cholesterol is important and necessary for human health, high levels of cholesterol in the blood have been linked to damage to arteries and cardiovascular disease.

The Cholesterol levels include:

• LDL (low-density lipoprotein cholesterol, 'bad' cholesterol)
• HDL (high-density lipoprotein cholesterol, 'good' cholesterol)
• Triglycerides (fats carried in the blood)

In humans, triglycerides are a mechanism for storing unused calories, and their high concentration in blood correlates with the consumption of starchy and other high carbohydrate foods.

High levels of triglycerides in the bloodstream have been linked to atherosclerosis and the risk of heart disease and stroke.

Heart rate is the number of heartbeats per unit of time, usually expressed as beats per minute (bpm). Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during physical exercise or sleep. The typical resting heart rate in adults is 60 to 100 bpm. Resting Heart Rates below 60 bpm may be referred to as bradycardia, while rates above 100 bpm at rest may be called tachycardia.

Caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks, and energy drinks, enjoy great popularity; 90% of adults consume caffeine daily. Ordinary consumption has low health risks, but consumption of large amounts of caffeine can lead to both positive and negative effects.

There are many social and environmental factors that affect whether people start smoking, but genetic factors play a significant part in how dependent on nicotine they'll become and how much they'll smoke.

Some people are naturally resistant to infection with HIV (the virus that causes AIDS) due to Delta32 mutation in the CCR5 gene that prevents the CCR5 protein from reaching the surface of the immune cells. The CCR5 protein is one of the proteins HIV uses to bind to and enter immune cells, so people who have two copies of CCR5Delta32 are almost completely resistant to HIV infection. The protection given by CCR5Delta32 mutation is incomplete though, because some strains of HIV can use another protein called CXCR4 to bind to immune cells.

Genetic resistance to malaria occurs through changes in human red blood cells that hinder the malaria parasite's ability to invade and replicate within these cells. Duffy Antigen mutation prevents one of the malaria parasite, Plasmodium vivax, from entering red blood cells. Having one abnormal allele of the hemoglobin beta gene (Sickle Cell Trait) gives protection against another common malaria parasite, Plasmodium falciparum.

Noroviruses, also called Norwalk-like viruses (NLV), are one of the main causes of non-bacterial epidemics of gastroenteritis or 'stomach flu'. These viruses usually appears in closed communities like schools, ships, military camps and such. Some people are resistant to the most common strains of Norovirus thanks to a mutation in FUT2 gene.

Peanut allergy is a type of food allergy and is among the most common food allergies found in children.

Agenesis of the Corpus Callosum with Peripheral Neuropathy is an autosomal recessive disease caused by mutations in the SLC12A6 gene and characterized by developmental abnormalities of the brain and progressive impairment of the ability to move, feel, and think clearly.

Bloom syndrome is a rare autosomal recessive disorder characterized by short stature and predisposition to the development of cancer. Complications of the disorder may include chronic lung problems, diabetes, and learning disabilities.

Canavan disease is an autosomal recessive degenerative disorder that causes progressive damage to nerve cells in the brain.

Congenital disorder of glycosylation type 1a is an autosomal recessive disorder caused by mutations in the PMM2 gene, which encodes a PMM protein.

D-Bifunctional protein deficiency is an autosomal recessive disorder caused by mutations in the HSD17B4 gene that disrupt the breakdown of fatty acids in peroxisomes. Most infants with DBP deficiency have low muscle tone and develop seizures within the first month of life, and usually do not live past the age of two years

Dihydrolipoamide dehydrogenase deficiency is an autosomal recessive disease caused by mutations in the DLD gene and results in the inability to metabolize certain amino acids and energy-containing molecules.

Dihydropyrimidine dehydrogenase deficiency (DPD deficiency) is an autosomal recessive metabolic disorder in which there is absent or significantly decreased activity of dihydropyrimidine dehydrogenase. People with this condition may develop life-threatening toxicity following exposure to 5-fluorouracil (5-FU), a chemotherapy drug that is used in the treatment of cancer.

Familial Dysautonomia is an inherited recessive disorder that affects the development and function of nerves throughout the body

Glycogen storage disease type I (GSD I) or von Gierke's disease, is a genetic disease results from deficiency of the enzyme glucose-6-phosphatase. This deficiency impairs the ability of the liver to produce free glucose from glycogen and from gluconeogenesis, causing severe hypoglycemia and an increased glycogen storage in liver and kidneys.

GRACILE syndrome is an autosomal recessive genetic disorder, caused by mutation in BCS1L gene.

Hereditary haemochromatosis is a genetic disorder that causes accumulation of iron in the body. It is characterized by an accelerated rate of intestinal iron absorption and progressive iron deposition in various tissues that typically begins to be expressed in the third to fifth decades of life, but may occur in children.

Hypertrophic cardiomyopathy is a disease of the myocardium in which a portion of the myocardium is thickened without any obvious cause. It is well known as a leading cause of sudden cardiac death in young athletes.

Maple syrup urine disease is an autosomal recessive metabolic disorder caused by mutations in the BCKDHB gene and affecting branched-chain amino acids

Mucolipidosis type IV (ML IV) is an autosomal recessive lysosomal storage disorder, caused by mutations in the MCOLN1 gene, which encodes a non-selective cation channel mucolipin1. People with the disorder have many symptoms including delayed psychomotor development and various ocular aberrations.

Nijmegen breakage syndrome is a rare autosomal recessive congenital disorder causing chromosomal instability due to a mutation in the NBS1 gene.

Rhizomelic chondrodysplasia punctata is a rare, developmental brain disorder characterized by systemic shortening of the proximal bones, seizures, recurrent respiratory tract infections, and congenital cataracts

Salla disease is an autosomal recessive lysosomal storage disease, caused by a mutation in the SLC17A5 gene and characterized by early physical impairment and mental retardation.

Sickle-cell disease (SCD), or sickle-cell anemia (SCA) is an autosomal recessive genetic blood disorder, characterized by red blood cells that assume an abnormal, sickle shape. The sickling occurs because of a mutation in the hemoglobin gene and decreases the cells' flexibility and results in a risk of various complications. There is a fitness benefit in carrying only a single sickle-cell gene (so called sickle cell trait). Those with only one of the two alleles of the sickle-cell disease are more resistant to malaria infection and show less severe symptoms when infected.

Torsion dystonia is a autosomal disorder caused by a mutation in the DYT1 gene and characterized by painful muscle contractions resulting in uncontrollable distortions.

Zellweger syndrome is a rare congenital disorder caused by mutations in genes that encode peroxins, proteins required for the normal assembly of peroxisomes. As a result of impaired peroxisome function, an individual's tissues and cells can accumulate very long chain fatty acids and branched chain fatty acids that are normally degraded in peroxisomes. The accumulation of these lipids can impair the normal function of multiple organ systems. In addition, these individuals can show deficient levels of plasmalogens that are especially important for brain and lung function.

Basal-cell carcinoma is a skin cancer and the most common type of cancer, although it rarely metastasizes or kills.

Breast cancer is a type of cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Worldwide, breast cancer comprises 22.9% of all cancers (excluding non-melanoma skin cancers) in women. The primary risk factors for breast cancer are female sex and older age, together with lifestyle and genetic factors.

Colorectal cancer, commonly known as colon cancer or bowel cancer, is a cancer from uncontrolled cell growth in the colon, rectum or in the appendix. Most colorectal cancer occurs due to lifestyle and increasing age with only a minority of cases associated with underlying genetic disorders.

Lung cancer is a disease characterized by uncontrolled cell growth in tissues of the lung. It's the deadliest type of cancer for both men and women, with more people die of lung cancer than of breast, colon and prostate cancers combined.The most common cause of lung cancer is long-term exposure to tobacco smoke which causes 80 to 90% of lung cancers. Nonsmokers account for 10 to 15% of lung cancer cases, and these cases are often attributed to a combination of genetic factors, radon gas, asbestos and air pollution.

Adenocarcinoma of the lung is a common histological form of lung cancer, accountable for approximately 40% of lung cancer cases.

Melanoma is a malignant tumor of skin cells that produce the dark pigment, melanin. It is less common than other skin cancers, but is much more dangerous if it is not found early, causing the majority of skin cancer-related deaths. A number of genetic mutations are known to greatly increase susceptibility to melanoma.

Ovarian cancer is a cancerous growth arising from the ovary. The risk of developing ovarian cancer appears to be affected by several factors, including age and genetic factors. Approximately 25% of ovarian cancer deaths occur in women between 35 and 54 years of age and more than 50% of the deaths occur in women between 55 and 74 years of age.

Prostate cancer is a form of cancer that develops in the prostate. It tends to develop in men over the age of fifty and globally is the sixth leading cause of cancer-related death in men. Many factors, including genetics and diet, have been implicated in the development of prostate cancer.

Atrial fibrillation is the most common cardiac arrhythmia. It is often associated with palpitations, fainting, chest pain, or congestive heart failure.

Venous thromboembolism is a disease that includes both deep vein thrombosis and pulmonary embolism. It results from a combination of hereditary and acquired risk factors. Pulmonary embolism is potentially life threatening if prompt medical attention is not received.

Age-related macular degeneration is a medical condition which usually affects older adults and results in a loss of vision in the center of the visual field due to damage to the retina. Macular degeneration can make it difficult or impossible to read or recognize faces.

Celiac disease is an autoimmune disorder of the small intestine that occurs in genetically predisposed people of all ages from middle infancy onward. Symptoms include chronic diarrhea, failure to thrive and fatigue.

Crohn's disease is a type of inflammatory bowel disease causing a wide variety of symptoms, primarily abdominal pain, diarrhea, vomiting, or weight loss. Crohn's disease is caused by a combination of environmental factors and genetic predisposition, mostly with variations of the NOD2 gene.

Type 1 diabetes is a form of diabetes mellitus that results from autoimmune destruction of insulin-producing beta cells of the pancreas. Eventually, type 1 diabetes is fatal unless treated with insulin. Type 1 diabetes is a polygenic disease, with many genes contribute to its onset together with environmental factors.

Type 2 Diabetes is a metabolic disorder that is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. It makes up about 90% of cases of diabetes. The development of type 2 diabetes is caused by a combination of lifestyle and genetic factors.

Gallstones are hard, pebble-like deposits that form inside the gallbladder. Presence of gallstones in the gallbladder may lead to acute cholecystitis. Presence of gallstones in other parts of the biliary tract can cause obstruction of the bile ducts, which can lead to serious conditions such as ascending cholangitis or pancreatitis.

Gout is a painful condition that occurs when the bodily waste product uric acid is deposited as needle-like crystals in the joints and/or soft tissues. In the joints, these crystals cause inflammatory arthritis, which leads to intermittent swelling, redness, heat, pain, and stiffness in the joints.

Usually, gout initially affects the joints of the big toe, but other joints and areas around can be affected as well.

There is a number of risk factors that are associated with gout, including genetics, age, weight, diet and alcohol consumption

Multiple sclerosis is an inflammatory disease in which the fatty myelin sheaths around the axons of the brain and spinal cord are damaged, leading to demyelination and scarring as well as a broad spectrum of signs and symptoms. Disease onset usually occurs in young adults, caused by a combination of genetic, environmental and infectious factors.

Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems. It increases the likelihood of various diseases, particularly heart disease, type 2 diabetes, obstructive sleep apnea, certain types of cancer, osteoarthritis and asthma. Obesity is most commonly caused by a combination of excessive food energy intake, lack of physical activity and genetic susceptibility.

Primary biliary cirrhosis is an autoimmune disease of the liver characterized by the slow progressive destruction of the small bile ducts within the liver. When these ducts are damaged, bile builds up in the liver and damages the tissue, which can lead to scarring, fibrosis and cirrhosis.

Psoriasis is an autoimmune disease that affects the skin causing accelerated growth of skin cells. The most common form, plaque psoriasis, is commonly seen as red and white hues of scaly patches appearing on the top first layer of the skin. Psoriasis has a large hereditary component, and many genes are associated with it.

Restless legs syndrome or Willis-Ekbom disease is a neurological disorder characterized by an irresistible urge to move one's body to stop uncomfortable or odd sensations. It most commonly affects the legs, but can affect the arms and torso as well.

Ulcerative colitis is a form of inflammatory bowel disease. It is a disease of the colon that includes characteristic ulcers. The main symptom of active disease is usually constant diarrhea mixed with blood, of gradual onset.