Mitochondrially encoded tRNA leucine 1 (UUA/G) also known as MT-TL1 is a transfer RNA which in humans is encoded by the mitochondrial MT-TL1 gene .
31-417: The MT-TL1 gene is located on the p arm of the mitochondrial DNA at position 12 and it spans 75 base pairs. The structure of a tRNA molecule is a distinctive folded structure which contains three hairpin loops and resembles a three-leafed clover . MT-TL1 is a small 75 nucleotide RNA (human mitochondrial map position 3230–3304) that transfers the amino acid leucine to a growing polypeptide chain at
62-457: A skeletal muscle developmental deficit. In population genetics , the concept of heterozygosity is commonly extended to refer to the population as a whole, i.e., the fraction of individuals in a population that are heterozygous for a particular locus. It can also refer to the fraction of loci within an individual that are heterozygous. In an admixed population , whose members derive ancestry from two or more separate sources, its heterozygosity
93-575: A chromosome is termed the p arm or p-arm , while the longer arm is the q arm or q-arm . The chromosomal locus of a typical gene, for example, might be written 3p22.1 , where: Thus the entire locus of the example above would be read as "three P two two point one". The cytogenetic bands are areas of the chromosome either rich in actively-transcribed DNA ( euchromatin ) or packaged DNA ( heterochromatin ). They appear differently upon staining (for example, euchromatin appears white and heterochromatin appears black on Giemsa staining ). They are counted from
124-556: A diploid organism is hemizygous when only one copy is present. The cell or organism is called a hemizygote . Hemizygosity is also observed when one copy of a gene is deleted, or, in the heterogametic sex , when a gene is located on a sex chromosome. Hemizygosity is not the same as haploinsufficiency , which describes a mechanism for producing a phenotype. For organisms in which the male is heterogametic, such as humans, almost all X-linked genes are hemizygous in males with normal chromosomes, because they have only one X chromosome and few of
155-432: A genotype consisting of only a single copy of a particular gene in an otherwise diploid organism, and nullizygous refers to an otherwise-diploid organism in which both copies of the gene are missing. A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes . An individual that is homozygous-dominant for a particular trait carries two copies of
186-605: A given locus are called heterozygous . The ordered list of loci known for a particular genome is called a gene map . Gene mapping is the process of determining the specific locus or loci responsible for producing a particular phenotype or biological trait . Association mapping , also known as "linkage disequilibrium mapping", is a method of mapping quantitative trait loci (QTLs) that takes advantage of historic linkage disequilibrium to link phenotypes (observable characteristics) to genotypes (the genetic constitution of organisms), uncovering genetic associations. The shorter arm of
217-418: A heterozygote will express only the trait coded by the dominant allele, and the trait coded by the recessive allele will not be present. In more complex dominance schemes the results of heterozygosity can be more complex. A heterozygous genotype can have a higher relative fitness than either the homozygous-dominant or homozygous-recessive genotype – this is called a heterozygote advantage . A chromosome in
248-507: A patient with the deficiency. This article incorporates text from the United States National Library of Medicine , which is in the public domain . Locus (genetics) In genetics , a locus ( pl. : loci ) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located. Each chromosome carries many genes, with each gene occupying a different position or locus; in humans,
279-402: A population: where n {\displaystyle n} is the number of individuals in the population, and a i 1 , a i 2 {\displaystyle a_{i1},a_{i2}} are the alleles of individual i {\displaystyle i} at the target locus. where m {\displaystyle m} is the number of alleles at
310-501: A single oocyte which subsequently splits into two morula . Zygosity is an important factor in human medicine. If one copy of an essential gene is mutated, the (heterozygous) carrier is usually healthy. However, more than 1,000 human genes appear to require both copies, that is, a single copy is insufficient for health. This is called haploinsufficiency . For instance, a single copy of the Kmt5b gene leads to haploinsufficiency and results in
341-400: A specific genotype. Heterozygous genotypes are represented by an uppercase letter (representing the dominant/wild-type allele) and a lowercase letter (representing the recessive/mutant allele), as in "Rr" or "Ss". Alternatively, a heterozygote for gene "R" is assumed to be "Rr". The uppercase letter is usually written first. If the trait in question is determined by simple (complete) dominance,
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#1732855309046372-419: Is homozygous-recessive for a particular trait carries two copies of the allele that codes for the recessive trait . This allele, often called the "recessive allele", is usually represented by the lowercase form of the letter used for the corresponding dominant trait (such as, with reference to the example above, "p" for the recessive allele producing white flowers in pea plants). The genotype of an organism that
403-462: Is nullizygous . The DNA sequence of a gene often varies from one individual to another. These gene variants are called alleles . While some genes have only one allele because there is low variation, others have only one allele because deviation from that allele can be harmful or fatal. But most genes have two or more alleles. The frequency of different alleles varies throughout the population. Some genes may have alleles with equal distributions. Often,
434-541: Is a rare mitochondrial disorder known to affect many parts of the body, especially the nervous system and the brain . Symptoms of MELAS include recurrent severe headaches , muscle weakness ( myopathy ), hearing loss , stroke -like episodes with a loss of consciousness , seizures , and other problems affecting the nervous system . A common mutation is A3243G. This mutation has been theorized to be associated with several other mitochondrial diseases , including diabetes mellitus and deafness . Diabetes mellitus and deafness
465-423: Is characterized by diabetes combined with hearing loss , particularly of high pitches. Additional symptoms include muscle weakness ( myopathy ) and various problems with a patient's eyes, heart, or kidneys. Other rare point variants on MT-TL1 gene were also described: m.3271 T > C, m.3291 T > C, m.3303 C > T, m.3256 C > T, and m.3260 A>G. MT-TP mutations may result in complex I deficiency of
496-521: Is from the Greek zygotos "yoked," from zygon "yoke") ( / z aɪ ˈ ɡ ɒ s ɪ t i / ) is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Most eukaryotes have two matching sets of chromosomes ; that is, they are diploid . Diploid organisms have the same loci on each of their two sets of homologous chromosomes except that
527-406: Is homozygous-recessive for a particular trait is represented by a doubling of the appropriate letter, such as "pp". A diploid organism is heterozygous at a gene locus when its cells contain two different alleles (one wild-type allele and one mutant allele) of a gene. The cell or organism is called a heterozygote specifically for the allele in question, and therefore, heterozygosity refers to
558-595: Is irrelevant for them. As discussed above, "zygosity" can be used in the context of a specific genetic locus (example ). The word zygosity may also be used to describe the genetic similarity or dissimilarity of twins. Identical twins are monozygotic , meaning that they develop from one zygote that splits and forms two embryos. Fraternal twins are dizygotic because they develop from two separate oocytes (egg cells) that are fertilized by two separate sperm . Sesquizygotic twins are halfway between monozygotic and dizygotic and are believed to arise after two sperm fertilize
589-476: Is known as being "identical by state", or IBS. Because the alleles of autozygous genotypes come from the same source, they are always homozygous, but allozygous genotypes may be homozygous too. Heterozygous genotypes are often, but not necessarily, allozygous because different alleles may have arisen by mutation some time after a common origin. Hemizygous and nullizygous genotypes do not contain enough alleles to allow for comparison of sources, so this classification
620-597: Is proven to be at least as great as the least heterozygous source population and potentially more than the heterozygosity of all the source populations. It reflects the contributions of its multiple ancestral groups. Admixed populations show high levels of genetic variation due to the fusion of source populations with different genetic variants. Typically, the observed ( H o {\displaystyle H_{o}} ) and expected ( H e {\displaystyle H_{e}} ) heterozygosities are compared, defined as follows for diploid individuals in
651-493: The Chinese hamster ovary cell line, a number of genetic loci are present in a functional hemizygous state, due to mutations or deletions in the other alleles. A nullizygous organism carries two mutant alleles for the same gene. The mutant alleles are both complete loss-of-function or 'null' alleles, so homozygous null and nullizygous are synonymous. The mutant cell or organism is called a nullizygote . Zygosity may also refer to
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#1732855309046682-562: The centromere out toward the telomeres . A range of loci is specified in a similar way. For example, the locus of gene OCA1 may be written "11q1.4-q2.1", meaning it is on the long arm of chromosome 11, somewhere in the range from sub-band 4 of region 1 to sub-band 1 of region 2. The ends of a chromosome are labeled "pter" and "qter" , and so "2qter" refers to the terminus of the long arm of chromosome 2. Michael, R. Cummings. (2011). Human Heredity . Belmont, California: Brooks/Cole. Heterozygote Zygosity (the noun, zygote ,
713-491: The mitochondrial respiratory chain , which may cause a wide variety of signs and symptoms affecting many organs and systems of the body, particularly the nervous system , the heart , and the muscles used for movement ( skeletal muscles ). These signs and symptoms can appear at any time from birth to adulthood. Phenotypes of the condition include encephalopathy , epilepsy , dystonia , hypotonia , myalgia , exercise intolerance , and more. A 3302A>G mutation has been found in
744-464: The ribosome site of protein synthesis during translation . Also, some studies showed that the MT-TL1 gene pathogenic variants could be attributed to the alterations of mTERF binding efficiency. Mutations in MT-TL1 can result in multiple mitochondrial deficiencies and associated disorders. It is associated with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes ( MELAS ). MELAS
775-448: The allele that codes for the dominant trait . This allele, often called the "dominant allele", is normally represented by the uppercase form of the letter used for the corresponding recessive trait (such as "P" for the dominant allele producing purple flowers in pea plants). When an organism is homozygous-dominant for a particular trait, its genotype is represented by a doubling of the symbol for that trait, such as "PP". An individual that
806-474: The different variations in the genes do not affect the normal functioning of the organism at all. For some genes, one allele may be common, and another allele may be rare. Sometimes, one allele is a disease -causing variation while another allele is healthy. In diploid organisms, one allele is inherited from the male parent and one from the female parent. Zygosity is a description of whether those two alleles have identical or different DNA sequences. In some cases
837-400: The origin(s) of the alleles in a genotype. When the two alleles at a locus originate from a common ancestor by way of nonrandom mating ( inbreeding ), the genotype is said to be autozygous . This is also known as being "identical by descent", or IBD. When the two alleles come from different sources (at least to the extent that the descent can be traced), the genotype is called allozygous . This
868-459: The same genes are on the Y chromosome . Transgenic mice generated through exogenous DNA microinjection of an embryo's pronucleus are also considered to be hemizygous, because the introduced allele is expected to be incorporated into only one copy of any locus. A transgenic individual can later be bred to homozygosity and maintained as an inbred line to reduce the need to confirm the genotype of each individual. In cultured mammalian cells, such as
899-431: The sequences at these loci may differ between the two chromosomes in a matching pair and that a few chromosomes may be mismatched as part of a chromosomal sex-determination system . If both alleles of a diploid organism are the same, the organism is homozygous at that locus. If they are different, the organism is heterozygous at that locus. If one allele is missing, it is hemizygous , and, if both alleles are missing, it
930-457: The term "zygosity" is used in the context of a single chromosome. The words homozygous , heterozygous , and hemizygous are used to describe the genotype of a diploid organism at a single locus on the DNA. Homozygous describes a genotype consisting of two identical alleles at a given locus, heterozygous describes a genotype consisting of two different alleles at a locus, hemizygous describes
961-425: The total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000. Genes may possess multiple variants known as alleles , and an allele may also be said to reside at a particular locus. Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at