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Sickle cell disease (SCD), also simply called sickle cell, is a group of hemoglobin-related blood disorders typically inherited. The most common type is known as sickle cell anemia. It results in an abnormality in the oxygen-carrying protein haemoglobin found in red blood cells.
Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous).
Mendelian traits in humans. A 50/50 chance of inheritance. Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition. [1]
Sickle cell – The gene for HbS associated with sickle-cell is today distributed widely throughout sub-Saharan Africa, the Middle East, and parts of the Indian subcontinent, where carrier frequencies range from 5–40% or more of the population.
Sickle cell anemia is a classic example of the mixed benefit given by the staying power of pleiotropic genes, as the mutation to Hb-S provides the fitness benefit of malaria resistance to heterozygotes as sickle cell trait, while homozygotes have significantly lowered life expectancy—what is known as "heterozygote advantage". Since both of ...
Expressivity (genetics) In genetics, expressivity is the degree to which a phenotype is expressed by individuals having a particular genotype. Alternatively, it may refer to the expression of a particular gene by individuals having a certain phenotype. Expressivity is related to the intensity of a given phenotype; it differs from penetrance ...
Examples of this type of disorder are albinism, medium-chain acyl-CoA dehydrogenase deficiency, cystic fibrosis, sickle cell disease, Tay–Sachs disease, Niemann–Pick disease, spinal muscular atrophy, and Roberts syndrome.
This is an example of balancing selection between the fierce selection against homozygous sickle-cell sufferers, and the selection against the standard HgbA homozygotes by malaria. The heterozygote has a permanent advantage (a higher fitness) wherever malaria exists.
e. A red tulip exhibiting a partially yellow petal due to a mutation in its genes. Mutation with double bloom in the Langheck Nature Reserve near Nittel, Germany. In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. [1]
Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population ( alleles ), a situation called polymorphism . No two humans are genetically identical. Even monozygotic twins (who develop from one zygote) have infrequent genetic differences due to mutations ...