Multiple metachromatic leucodystrophy alleles in an unaffected subject: a case of dispermic chimaerism

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...

Like autosomes, sex chromosomes contain a variety of genes necessary for normal body function. When a mutation in one of these genes results in biological deficits, the disorder is considered sex-linked.Y chromosome mutations are called “Y-linked” and only affect males since they alone carry a copy of that chromosome. Mutations to the relatively small Y chromosome can impact male sexual function and secondary sex characteristics. Y-chromosome infertility is a disorder that affects sperm...

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.

A pedigree is a diagram displaying a family’s history of a trait. Analyzing pedigrees can reveal (1) whether a trait is dominant or recessive, (2) the type of chromosome, autosomal or sex, a trait is linked to, (3) genotypes of family members, and (4) probabilities of phenotypes in future generations. For families with a history of autosomal or sex-linked diseases, this information can be crucial to family planning.Pedigrees Display Family HistoriesIn various plant and animal species,...

A complementation test is a simple cross to identify whether the two mutations are located on the same gene or different genes. It was first performed by Edward Lewis in the 1940s while working on fruit flies. He developed the test to identify the location and arrangement of different mutations on chromosomes.
Organisms heterozygous for different mutations are crossed pairwise in all combinations. If present on different genes, the mutations can complement each other by providing the missing...