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Originally, a heterozygous state is required and indicates the absence of a functional tumor suppressor gene copy in the region of interest. However, many people remain healthy with such a loss, because there still is one functional gene left on the other chromosome of the chromosome pair.
However, convincing evidence indicates, in areas with persistent malaria outbreaks, individuals with the heterozygous state have a distinct advantage (and this is why individuals with heterozygous alleles are far more common in these areas). [13] [14] Those with the benign sickle trait possess a resistance to malarial infection. The pathogen ...
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 a genotype consisting of only a single copy of a particular gene in an ...
In medical genetics, compound heterozygosity is the condition of having two or more heterogeneous recessive alleles at a particular locus that can cause genetic disease in a heterozygous state; that is, an organism is a compound heterozygote when it has two recessive alleles for the same gene, but with those two alleles being different from each other (for example, both alleles might be ...
Haploinsufficiency may arise from a de novo or inherited loss-of-function mutation in the variant allele, such that it yields little or no gene product (often a protein). Although the other, standard allele still produces the standard amount of product, the total product is insufficient to produce the standard phenotype.
For the alleles that confer an advantage in the heterozygous and/or homozygous-dominant state, the fitness of the homozygous-recessive state may even be zero (meaning sterile or unviable offspring). An example of inbreeding depression is shown in the image. In this case, a is the recessive allele which has negative effects.
Because loss of NEMO function is lethal, only heterozygous females or males with XXY karyotype or mosaicism for this gene survive and exhibit symptoms of incontinetia pigmenti, such as skin lesions and abnormalities in hair, teeth, and nails. There are a variety of mutations that may cause the symptoms of IP.
[15] [16] In the fruit fly Drosophila melanogaster, where a fly possessing two X chromosomes is a female and a fly possessing a single X chromosome is a sterile male, a loss of an X chromosome early in embryonic development can result in sexual mosaics, or gynandromorphs. [5] [17] Likewise, a loss of the Y chromosome can result in XY/X mosaic ...