Genes recessive

Tsuchida, K., Katagiri, C., Tanaka, Y. et al. 2004b. The basis for colorless hemolymph and cocoons in the Y-gene recessive Bombyx mori mutants A defect in the cellular uptake of carotenoids. J. Insect Physiol., 50(10) 975-983. 

Heavy metals possess mutagenic effect. The assessment of mutagenic effect was assessed through evaluation of genes recessive mutation frequency in the micronucleus in oral mucous cells of children living at the tested areas (Tabl. 3). 

RECESSIVE Pertaining to the member of a pair of genes that fails to express itself in heterozygotes in the presence of its dominant allele pertaining to the trait produced by a recessive gene recessive genes ordinarily express themselves only in the homozygous state. (See also DOMINANT)... 

Myotonia is muscle stiffness, in which muscle relaxation after voluntary contraction is impaired. Mutations in several ion channel genes (Cl, Na, Ca, K channels) can cause myotonias, which can sometimes be differentiated clinically (e.g. paramyotonia is cold-sensitive). C1C-1 mutations cause pure myotonia congenita which is not sensitive to temperature. Channel myotonia comes in a recessive (Becker type)... 

PC C56 C56.002 DJ-1 putative peptidase Mutations in the gene cause PARK7, an autosomal recessive form of early-on set parkinsonism... 

Parkin is a ubiquitin ligase encoded by a gene affected in autosomal recessive juvenile parkinsonism (AR-JP). This gene is located on chromosome 6 and encodes a protein of 465 amino acid residues with moderate similarity to ubiquitin at the amino terminus and a RING-finger motif at the carboxy terminus. 

While it is probably rarer than recessively inherited disease, families with autosomal dominant LGD have been described, and in these families the disease is usually relatively mild. In one large family with dominant disease and the unusual additional feature of dysarthria, a locus has been identified on chromosome 5. The genes responsible for this condition in other families have not yet been localized. 

Genetic transmission in nemaline myopathy is the subject of some uncertainty. A Japanese study of 50 pedigrees came to the conclusion that autosomal dominant with reduced penetrance was the most probable mode. However a Finnish study presented evidence for autosomal recessive transmission. There is no evidence that severe and mild forms are genetically distinct and several pedigrees contain members showing widely differing clinical severity. A candidate gene for autosomal dominant nemaline myopathy has been localized to chromosome Iq 21—23. 

The genetic trait for MH is not sex-linked and both men and women can inherit MH. Inheritance in humans appears to be autosomal dominant with variable penetrance. Studies of large families have documented an autosomal dominant pattern. McPherson and Taylor (1982) studied 93 families in whom MH occurred. Even though various patterns of inheritance did emerge in the study we should assume that 50% of children are at risk in MH susceptible families. Kalow and Britt (1992) suggested that, in some families, at least two different non-allelic genes are likely to be present, one of which is probably autosomal dominant but rare, and the other autosomal recessive but common. 

In general, the porphyrias described are inherited in an autosomal dominant manner, with the exception of congenital erythropoietic porphyria, which is inherited in a recessive mode. The precise abnormalities in the genes directing synthesis of the enzymes involved in heme biosynthesis have been determined in some instances. Thus, the use of appropriate gene probes has made possible the prenatal diagnosis of some of the porphyrias. 

Type I Crigler-Najjar syndrome is a rare autosomal recessive disorder. It is characterized by severe congenital jaundice (serum bilirubin usually exceeds 20 mg/dL) due to mutations in the gene encoding bilirubin-UGT activity in hepatic tissues. The disease is often fatal within the first 15 months of life. Children with this condition have been treated with phototherapy, resulting in some reduction in plasma bilirubin levels. Phenobarbital has no effect on the formation of bilirubin glucuronides in patients with type I Crigler-Najjar syndrome. A liver transplant may be curative. 

This benign autosomal recessive disorder consists of conjugated hyperbilirubinemia in childhood or during adult life. The hyperbilirubinemia is caused by mutations in the gene encoding MRP-2 (see above), the protein involved in the secretion of conjugated bilirubin into bile. The centrilobular hepatocytes contain an abnormal black pigment that may be derived from epinephrine. 

The genes responsible for production of the ABO substances are present on the long arm of chromosome 9. There are three alleles, two of which are codominant (A and B) and the third (O) recessive these ultimately determine the four phenotypic products the A, B, AB, and O substances. 

Figure 52-7. Simplified scheme of the sequence of events involved in the causation of chronic granulomatous disease (MIM 306400). Mutations in any of the genes for the four polypeptides involved (two are components of cytochrome b55gand two are derived from the cytoplasm) can cause the disease. The polypeptide of 91 kDa is encoded by a gene in the X chromosome approximately 60% of cases of chronic granulomatous disease are X-linked, with the remainder being inherited in an autosomal recessive fashion.

Extensive linkage studies Large families with defined pedigrees are desirable. Dominant genes are easier to recognize than recessives. 

Biochemical Analysis> The second principal use of cultured amniotic fluid cells is to determine the biochemical status of the fetus. Again, it should be pointed out that the individual biochemical disorders are quite low in incidence, but many of them are very serious in their manifestations and can occur with relatively high frequencies in specific families. If two parents are carriers of a gene for an autosomal recessive condition, then the risk to each child of having the disorder is 25%. 

Fig. 25.8 (a) Normal metabolism, in which phenylalanine is converted by phenylalanine 4-mono-oxygenase to tyrosine, (b) Phenylketonuria, in which there is a transamination reaction between phenylalanine and a-ketoglutaric acid. Phenylalanine 4-mono-oxygenase is absent in about 1 in every 10000 human beings because of a recessive mutant gene. 

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