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| Homozygous is a term used in genetics to describe the [[Genome]] of an individual organism were two indistinguishable [[Allele]] are found on the locus of the same gene. The alleles are genetically very similar if not identical and so code for the same things and express the same [[Phenotypes]]. If both alleles are the same then the phenotype of these alleles will be shown in the individual whether the alleles are [[Recessive]] or [[Dominant]].
| | See [[Recessive_gene|Recessive Gene]] |
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| [[Recessive]] is also a term used in genetics which describes the characteristics and type of allele present in the genotype of an individual. A recessive allele is where homozygosity is required to shown the alleles phenotype in the organism as if only one recessive allele is present its [[Expression]] would be suppressed. In other words two copies of the recessive allele are required in order to show the characteristics they express as the organisms phenotype. If the organism were to have a [[Heterozygous]] gene with one dominant and one recessive allele then the dominant allele’s phenotype would be expressed and this would be at the expense of the recessive allele as its phenotype would be masked. There are many examples of recessive alleles that can cause disease or [[Mutations]] in organisms such as [[Cystic Fibrosis]] (lack of [[CFTR|CFTR]]), Albinism (lack of the pigment melanin) and Tay-Sachs disease (causes damage to the nervous system and at the moment always fatal) but the recessive alleles that cause these mutations are very rare and only occur if both parent organisms are carriers of the recessive allele or possess the mutation themselves. Almost always, the disorders that are expressed due to the recessive genotype are fatal. In the case of [[Cystic Fibrosis|Cystic Fibrosis]], treatment can improve life expectancy minorly, but ultimately, the patient dies. Infants having [[Sickle cell anaemia|Sickle Cell Anaemia]] survive only for a couple of days after birth. | |
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| Therefore Homozygous Recessive refers to two indistinguishable copies of the same recessive allele found on a locus of an individual’s genome. Due to it being Homozygous the phenotype characteristics of the recessive alleles will be shown in the organism and the recessive gene will be expressed<ref>Daniel L. Hartyl and Maryellen Ruvolo, 2012, Genetics: Analysis of Genes and Genomes, 8th Edition, Jones and Bartlett Learning</ref>.<br>
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| === References ===
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| <references />
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Latest revision as of 17:15, 22 October 2018