Quantitative traits
Polygenic inheritance, also known as quantitative or multifactorial inheritance refers to inheritance of a phenotypic A phenotype is any observable characteristic or trait of an organism: such as its morphology, development, biochemical or physiological properties, or behavior. Phenotypes result from the expression of an organism's genes as well as the influence of environmental factors and possible interactions between the two. The genotype of an organism is the characteristic (trait) that is attributable to two or more genes A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring. A modern working definition of a gene is "a locatable region of genomic sequence, corresponding to a unit of inheritance, which is associated with and their interaction with the environment. Unlike monogenic traits, polygenic traits do not follow patterns of Mendelian inheritance Mendelian inheritance is a set of primary tenets relating to the transmission of hereditary characteristics from parent organisms to their children; it underlies much of genetics. They were initially derived from the work of Gregor Mendel published in 1865 and 1866 which was "re-discovered" in 1900, and were initially very controversial (qualitative traits). Instead, their phenotypes typically vary along a continuous gradient depicted by a bell curve In probability theory and statistics, the normal distribution or Gaussian distribution is a continuous probability distribution that describes data that clusters around a mean or average. The graph of the associated probability density function is bell-shaped, with a peak at the mean, and is known as the Gaussian function or bell curve.[1]
An example of a polygenic trait is human skin color. Many genes factor into determining a person's natural skin color, so modifying only one of those genes changes the color only slightly. Many disorders with genetic components A genetic disorder is an illness caused by abnormalities in genes or chromosomes. While some diseases, such as cancer, are due in part to a genetic disorders, they can also be caused by environmental factors. Most disorders are quite rare and affect one person in every several thousands or millions. Some types of recessive gene disorders confer an are polygenic, including autism Autism is a brain development disorder characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism involves many parts of the brain; how this occurs is not well understood. The two other autism spectrum disorders are Asperger syndrome,, cancer Cancer is a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors,, diabetes Diabetes mellitus —often referred to simply as diabetes—is a condition in which the body does not produce enough, or properly respond to, insulin, a hormone produced in the pancreas. Insulin enables cells to absorb glucose in order to turn it into energy. In diabetes, the body can't use its own insulin as well as it should, doesn't make enough and numerous others. Most phenotypic characteristics are the result of the interaction of multiple genes.
Examples of disease processes generally considered to be results of multifactorial etiology Etiology is the study of causation, or origination. The word is derived from the Greek αἰτιολογία, aitiologia, "giving a reason for" (αἰτία, aitia, "cause"; and -λογία, -logia):
Congenital malformation
- Cleft palate Cleft lip and cleft palate (palatoschisis) (colloquially known as harelip), which can also occur together as cleft lip and palate, are variations of a type of clefting congenital deformity caused by abnormal facial development during gestation. A cleft is a fissure or opening—a gap. It is the non-fusion of the body's natural structures that form[2] [3]
- Congenital dislocation of the hip Hip dysplasia, developmental dysplasia of the hip or congenital dysplasia of the hip (CDH) is a congenital or acquired deformation or misalignment of the hip joint[4]
- Congenital heart defects
- Neural tube defects A neural tube defect will occur in human embryos if there is an interference with the closure of the neural tube that occurs around the 28th day after fertilization. The incidence of neural tube defects is 2.6 in 1,000 worldwide.[citation needed]
- Pyloric stenosis Pyloric stenosis is a condition that causes severe vomiting in the first few months of life. There is narrowing (stenosis) of the opening from the stomach to the intestines, due to enlargement (hypertrophy) of the muscle surrounding this opening (the pylorus, meaning "gate"), which spasms when the stomach empties. It is uncertain whether
- Talipes A clubfoot, Giles Smith syndrome or talipes equinovarus , is a birth defect. TEV is classified into 2 groups: Postural TEV or Structural TEV. Without treatment, persons afflicted often appear to walk on their ankles, or on the sides of their feet. It is a common birth defect, occurring in about one in every 1,000 live births. Approximately 50% of
Adult onset diseases
- Diabetes Mellitus Diabetes mellitus —often referred to simply as diabetes—is a condition in which the body does not produce enough, or properly respond to, insulin, a hormone produced in the pancreas. Insulin enables cells to absorb glucose in order to turn it into energy. In diabetes, the body can't use its own insulin as well as it should, doesn't make enough[3]
- Cancer Cancer is a class of diseases in which a group of cells display uncontrolled growth (division beyond the normal limits), invasion (intrusion on and destruction of adjacent tissues), and sometimes metastasis (spread to other locations in the body via lymph or blood). These three malignant properties of cancers differentiate them from benign tumors,[3]
- Epilepsy Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or synchronous neuronal activity in the brain. About 50 million people worldwide have epilepsy, with almost 90% of these people being in developing countries. Epilepsy is more
- Glaucoma Glaucoma refers to a group of diseases that affect the optic nerve and involves a loss of retinal ganglion cells in a characteristic pattern. It is a type of optic neuropathy. Raised intraocular pressure is a significant risk factor for developing glaucoma . One person may develop nerve damage at a relatively low pressure, while another person may
- hypertension Hypertension, also referred to as high blood pressure, HTN or HPN, is a medical condition in which the blood pressure is chronically elevated. In current usage, the word "hypertension" without a qualifier normally refers to systemic, arterial hypertension
- Ischaemic heart disease Ischaemic or ischemic heart disease , or myocardial ischaemia, is a disease characterized by reduced blood supply to the heart muscle, usually due to coronary artery disease (atherosclerosis of the coronary arteries). Its risk increases with age, smoking, hypercholesterolaemia (high cholesterol levels), diabetes, hypertension (high blood pressure)
- Manic depression
- Schizophrenia Schizophrenia , from the Greek roots skhizein (σχίζειν, "to split") and phrēn, phren- (φρήν, φρεν-; "mind") is a psychiatric diagnosis that describes a mental disorder characterized by abnormalities in the perception or expression of reality. Distortions in perception may affect all five senses, including sight,
Multifactorially inherited diseases are said to constitute the majority of all genetic disorders affecting humans which will result in hospitalization or special care of some kind[5] [6].
<<Table of Contents Inheritance of quantitative traits or polygenic inheritance refers to the inheritance of a phenotypic characteristic that varies in degree and can be attributed to the interactions between two or more genes and their environment. Though not necessarily genes themselves, quantitative trait loci are stretches of DNA that are closely linked to the | Next>> | Show All>>
