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Encyclopedia > Recessive gene

In genetics, the term "recessive gene" refers to an allele that causes a phenotype (visible or detectable characteristic) that is only seen in a homozygous genotype (an organism that has two copies of the same allele) and never in a heterozygous genotype. Every person has two copies of every gene on autosomal chromosomes, one from mother and one from father. If a genetic trait is recessive, a person needs to inherit two copies of the gene for the trait to be expressed. Thus, both parents have to be carriers of a recessive trait in order for a child to express that trait. If both parents are carriers, there is a 25% chance with each child to show the recessive trait. Image File history File links Information_icon. ... Wikipedia does not have an article with this exact name. ... It has been suggested that dominant gene be merged into this article or section. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... In genetics, an allele (pronounced al-eel) is any one of a number of viable DNA codings occupying a given locus (position) on a chromosome. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ... The genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. ... An autosome is a non-sex chromosome. ...


The term "recessive gene" is part of the laws of Mendelian inheritance created by Gregor Mendel. Examples of recessive genes in Mendel's famous pea plant experiments include those that determine the color and shape of seed pods, and plant height. This article does not cite its references or sources. ... Gregor Johann Mendel (July 20[1], 1822 – January 6, 1884) was an Augustinian abbot who is often called the father of modern genetics for his study of the inheritance of traits in pea plants. ...

Contents

Autosomal recessive gene

Autosomal recessive is a mode of inheritance of genetic traits located on the autosomes (the 22 non-sex determining chromosomes). Inheritance is the practice of passing on property, titles, debts, and obligations upon the death of an individual. ... An autosome is a non-sex chromosome. ... Figure 1: A representation of a condensed eukaryotic chromosome, as seen during cell division. ...


In opposition to autosomal dominant trait, a recessive trait only becomes phenotypically apparent when two copies of a gene (two alleles) are present. In other words, the subject is homozygous for the trait. An autosomal dominant gene is one that occurs on an autosomal (non-sex determining) chromosome. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...


Recessive genes will also show a horizontal inheritance on a pedigree chart.


The frequency of the carrier state can be calculated by the Hardy-Weinberg formula: p2 + 2pq + q2 = 1 (p is the frequency of one pair of alleles, and q = 1 − p is the frequency of the other pair of alleles.) Hardy–Weinberg principle for two alleles: the horizontal axis shows the two allele frequencies p and q, the vertical axis shows the genotype frequencies and the three possible genotypes are represented by the different glyphs In population genetics, the Hardy–Weinberg principle (HWP) (also Hardy–Weinberg equilibrium (HWE), or Hardy...


Image:autorecessive-3.png Image File history File links Autorecessive-3. ...


Recessive genetic disorders occur when both parents are carriers and each contributes an allele to the embryo. As both parents are heterozygous for the disorder, the chance of two disease alleles landing in one of their offspring is 25% (in autosomal dominant traits this is higher). 50% of the children (or 2/3 of the remaining ones) are carriers. When one of the parents is homozygous, the trait will only show in his/her offspring if the other parent is also a carrier. In that case, the chance of disease in the offspring is 50%. A genetic disorder, or genetic disease, is a disease caused by abnormal expression of one or more genes in a person causing a clinical phenotype. ... In genetics, an allele (pronounced al-eel) is any one of a number of viable DNA codings occupying a given locus (position) on a chromosome. ... This article or section is in need of attention from an expert on the subject. ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ... An autosomal dominant gene is one that occurs on an autosomal (non-sex determining) chromosome. ... Homozygote cells are diploid or polyploid and have the same alleles at a locus (position) on homologous chromosomes. ...


Nomenclature

Technically, the term "recessive gene" is imprecise because it is not the gene that is recessive but the phenotype (or trait). It should also be noted that the concepts of recessiveness and dominance were developed before a molecular understanding of DNA and before molecular biology, thus mapping many newer concepts to "dominant" or "recessive" phenotypes is problematic. Many traits previously thought to be recessive have mild forms or biochemical abnormalities that arise from the presence of the one copy of the allele. This suggests that the dominant phenotype is dependent upon having two dominant genes and the presence of one dominant and one recessive gene creates some blending of both dominant and recessive traits. This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions for the biological development of a cellular form of life or a virus. ... Molecular biology is the study of biology at a molecular level. ...

  T t
T T T T t
t T t t t

Recessive genes are usually represented by a lowercase letter in a Punnett square, as opposed to the uppercase letters of dominant genes (see example at right). Using the letter "T" as an example, only in "tt" (the homozygous recessive genotype, indicated by blue) would the recessive physical trait appear. The form "Tt" is called heterozygous (indicated by magenta with a red border), and, even though a recessive allele is present, the dominant gene is the one that appears (becomes the phenotype). The homozygous dominant genotype is "TT" (indicated by red). A Punnett square is genetic tool designed by Reginald Punnett that biologists continue to use in order to determine the probability of an offspring expressing a particular genotype. ... Heterozygote cells are diploid or polyploid and have different alleles at a locus (position) on homologous chromosomes. ...


Examples

Pea Plant

Gregor Mendel performed many experiments on pea plants (Pisum sativum) while researching traits, chosen because of the simple and low variety of characteristics, as well as the short period of germination. He experimented with color (green vs. yellow), size (short vs. tall), pea texture (smooth vs. wrinkled), and many others. By good fortune, the characteristics displayed by these plants clearly exhibited a dominant and recessive form. This is not true for many organisms. Gregor Johann Mendel (July 20[1], 1822 – January 6, 1884) was an Augustinian abbot who is often called the father of modern genetics for his study of the inheritance of traits in pea plants. ... Binomial name Pisum sativum A pea (Pisum sativum) is the small, edible round green seed which grows in a pod on a leguminous vine, hence why it is called a legume. ...


For example, when testing the color of the pea plants, he chose two yellow plants, since yellow was more common than green. He mated them, and examined the offspring. He continued to mate only those that appeared yellow, and eventually, the green ones would stop being produced. He also mated the green ones together and determined that only green ones were produced.


Mendel determined that this was because green was a recessive trait which only appeared when yellow, the dominant trait, was not present. Also, he determined that the dominant trait would be displayed whether or not the recessive trait was there.


Autosomal recessive disease

Dominance/recessiveness refers to phenotype, not genotype. An example to prove the point is sickle cell anemia. The sickle cell genotype is caused by a single base pair change in the beta-globin gene: normal=GAG (glu), sickle=GTG (val). There are several phenotypes associated with the sickle genotype: - Sickle-shaped red blood cells Sickle cell anemia (American English), sickle cell anaemia (British English) or sickle cell disease is a genetic disease in which red blood cells may change shape under certain circumstances. ... Glutamine is one of the 20 amino acids encoded by the standard genetic code. ... Valine is one of the 20 natural amino acids, and is coded for in DNA. Nutritionally, valine is also an essential amino acid. ...

  1. anemia (a recessive trait)
  2. blood cell sickling (co-dominant)
  3. altered beta-globin electrophoretic mobility (co-dominant)
  4. resistance to malaria (dominant)

This example demonstrates that one can only refer to dominance/recessiveness with respect to individual phenotypes.


Other recessive disorders: -

Tay-Sachs disease (abbreviated TSD, also known as GM2 gangliosidosis) is a genetic disorder, fatal in its most common variant known as Infantile Tay-Sachs disease. ... In medicine (genetics and pediatrics) chronic granulomatous disease (CGD) is a hereditary disease where neutrophil granulocytes are unable to destroy ingested pathogens. ... Thalassemia (American English) (or thalassaemia in British English) is an inherited disease of the red blood cells. ... It has been suggested that this article or section be merged into Bloom syndrome. ... Alpha 1-antitrypsin deficiency (A1AD or Alpha-1) is a genetic disorder caused by reduced levels of alpha 1-antitrypsin in the blood. ... Haemochromatosis, also spelled hemochromatosis, is a hereditary disease characterized by improper processing by the body of dietary iron which causes iron to accumulate in a number of body tissues, eventually causing organ dysfunction. ... Wilsons disease or lentigohepatic degeneration is an autosomal recessive hereditary disease, with an incidence of about 1 in 30,000. ... The mucopolysaccharidoses are inborn errors of metabolism resulting from the deficiency of specific lysosomal enzymes needed in glycosaminoglycan catabolism. ... Glycogen storage disease is any one of several inborn errors of metabolism that result from enzyme defects that affect the processing of glycogen synthesis or breakdown within muscles, liver, and other cell types. ... Homocystinuria, also known as Cystathionine beta synthase deficiency, is inherited disorder of the metabolism of the amino acid methionine. ... Congenital adrenal hyperplasia (CAH) refers to any of several autosomal recessive diseases resulting from defects in steps of the synthesis of cortisol from cholesterol by the adrenal glands. ... Dubin-Johnson syndrome is an autosomal recessive disease which presents shortly after birth with an increase of conjugated bilirubin without elevation of liver enzymes (ALT, AST). ... Fanconi anemia (FA) is a rare genetic disease that affects children and adults from all ethnic backgrounds. ... Galactosemia is a rare genetic metabolic disorder which affects an individuals ability to properly digest the sugar galactose. ... Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked recessive hereditary disease featuring nonimmune hemolytic anemia in response to a number of causes. ... Phenylketonuria (PKU; ) is a human genetic disorder, in which the body lacks phenylalanine hydroxylase, the enzyme necessary to metabolize phenylalanine to tyrosine. ... Albinism (from Latin albus, meaning white) is a lack of pigmentation in the eyes, skin and/or hair. ... Rotor syndrome is a rare, benign autosomal recessive disorder of unknown origin. ... Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder that affects groups of patients originating from around the Mediterranean Sea (hence its name). ... Pendred syndrome or Pendred disease is a genetic disorder leading to sensorineural hearing loss and goitre with occasional hypothyroidism. ... Spinal Muscular Atrophy (SMA) is a term applied to a number of different disorders, all having in common a genetic cause and the manifestation of weakness due to loss of the motor neurons of the spinal cord and brainstem. ... Xeroderma pigmentosum, or XP, is a genetic disorder of DNA repair in which the bodys normal ability to fix mutations caused by ultraviolet (UV) light is disabled. ... Friedreichs ataxia is an inherited disease that causes progressive damage to the nervous system resulting in symptoms ranging from gait disturbance and speech problems to heart disease. ...

See also

In genetics, the term dominant gene refers to the allele that causes a phenotype that is seen in a heterozygous genotype. ... It has been suggested that this article or section be merged with dominance relationship. ... It has been suggested that dominant gene be merged into this article or section. ... Sex-linked genes are those carried on the mammalian X chromosome but not the Y chromosome. ... // Mitochondrial DNA (mtDNA) is DNA that is located in mitochondria. ...

References


  Results from FactBites:
 
Recessive gene - Wikipedia, the free encyclopedia (825 words)
Autosomal recessive is a mode of inheritance of genetic traits located on the autosomes (the 22 non-sex determining chromosomes).
Technically, the term "recessive gene" is imprecise because it is not the gene that is recessive but the phenotype (or trait).
Recessive genes are usually represented by a lowercase letter in a Punnett square, as opposed to the uppercase letters of dominant genes (see example at right).
Recessive Gene Transmission - Picture - MSN Encarta (264 words)
In these cases, two copies of the recessive gene are required for the disease to occur.
A person who has just one copy of the recessive gene is termed a carrier, since he or she carries the gene but is not affected by it.
The children on the far left received the recessive gene from their father and the dominant gene from their mother, and are therefore carriers.
  More results at FactBites »

 
 

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14th March 2011
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