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Epistasis

Epistasis

In addition to multiple alleles at the same locus influencing traits, numerous genes or alleles at different locations may interact and influence phenotypes in a phenomenon called epistasis. For example, rabbit fur can be black or brown depending on whether the animal is homozygous dominant or heterozygous at a TYRP1 locus. However, if the rabbit is also homozygous recessive at a locus on the tyrosinase gene (TYR), it will have an unshaded coat that appears white, regardless of its TYRP1...

Genetic Lingo

Genetic Lingo

Incomplete Dominance

Incomplete Dominance

Gregor Mendel's work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid cell has two variants called alleles inherited from each parent. He suggested that amongst these two alleles, one allele is dominant in character and the other recessive. The combination of alleles determines the phenotype of a gene in an organism.

Lethal Alleles

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cuénot discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is responsible for the color of the coat in mice. This gene codes for an agouti-signaling protein, which is responsible for melanin distribution in mammals. The wild-type allele gives rise to gray-brown coat color in mice, while the mutant allele gives rise to yellow coat color. In addition to coat color, the agouti gene is associated with the yellow...

Epistasis Analysis

Epistasis Analysis

Although Mendel chose seven unrelated traits in peas to study gene segregation, most traits involve multiple gene interactions that create a spectrum of phenotypes. When the interaction of various genes or alleles at different locations influences a phenotype, this is called epistasis. Epistasis often involves one gene masking or interfering with the expression of another (antagonistic epistasis). Epistasis often occurs when different genes are part of the same biochemical pathway. The...

X-linked Traits

X-linked Traits

In most mammalian species, females have two X sex chromosomes and males have an X and Y. As a result, mutations on the X chromosome in females may be masked by the presence of a normal allele on the second X. In contrast, a mutation on the X chromosome in males more often causes observable biological defects, as there is no normal X to compensate. Trait variations arising from mutations on the X chromosome are called “X-linked”.

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Blue cone monochromacy: causative mutations and associated phenotypes.

Jessica C Gardner¹, Michel Michaelides, Graham E Holder

¹Institute of Ophthalmology, University College London, London, UK.

Molecular Vision

|May 8, 2009

Summary

Blue cone monochromatism (BCM) in three families was assessed. Genetic analysis revealed inactivating mutations in opsin genes, with one family showing a novel mutation causing slow disease progression.

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Area of Science:

Ophthalmology
Genetics
Molecular Biology

Background:

Blue cone monochromatism (BCM) is a rare inherited retinal disorder.
It is characterized by reduced visual acuity, photophobia, and impaired color vision.
BCM results from mutations in the genes responsible for cone photoreceptor function.

Purpose of the Study:

To conduct a phenotypic evaluation of individuals from three British families with BCM.
To identify the specific molecular genetic causes of BCM in these families.

Main Methods:

Clinical examination, electrophysiological, and psychophysical testing were performed on affected family members.
DNA was extracted for molecular analysis.
Polymerase chain reaction (PCR) amplified opsin genes and locus control regions, followed by direct sequencing.

Main Results:

Genetic analysis identified unequal crossovers in the opsin gene array with inactivating mutations in all three families.
Families 1 and 3 had typical BCM with a Cys203Arg (C203R) mutation in hybrid genes.
Family 2 presented a novel mutation (lacking exon 2) associated with a slowly progressive BCM phenotype.

Conclusions:

Two families had BCM caused by hybrid genes with the common C203R mutation.
A novel BCM mutation involving a deleted exon 2 was identified in a family with slow disease progression.
This novel mutation may lead to cone cell loss through abnormal protein accumulation, representing the first report of slow progression in BCM associated with this mutation class.