PubMed · 3173489
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R W Michelmore, D V Shaw. 1988-10-20. Quantitative genetics. Character dissection.. https://doi.org/10.1038/335672a0
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In the Admixture Model, the probability that an individual carries a certain allele at a specific marker depends on the allele frequencies in K ancestral populations and the proportion of the individual's genome originating from these populations. The markers are assumed to be independent. The Linkage Model is a Hidden Markov Model that extends the Admixture Model by incorporating linkage between neighboring loci. We prove consistency and asymptotic normality of maximum likelihood estimators for the ancestry of individuals in the Linkage Model, complementing earlier results by (Pfaff et al., 2004; Pfaffelhuber and Rohde, 2022; Heinzel, 2025) for the Admixture Model. These results are used to prove that a statistical test that allows for model selection between the Admixture Model and the Linkage Model is an asymptotic level-α-test. Finally, we demonstrate the practical relevance of our results by applying the test to real-world data from The 1000 Genomes Project Consortium (2015).
A family with X-linked recessive mental retardation (XLMR) without other obvious manifestations (MRX20) was studied with 14 short tandem repeat polymorphism (STRP) markers. Two-point lod scores above 3 were obtained with DXS1003, DXYS1, DXS3, and DXS458. A multipoint lod score of 4.25 was obtained with peak at DXS1003. Recombination events identify a 55.6 cM interval between DXS1068 and DXS454, while a one unit support interval identifies 40 cM between MAOA and DXS458.
OBJECTIVES: To confirm linkage of the locus of the major form of hyperekplexia to markers on chromosome 5q, to screen for a point mutation in the gene encoding the alpha 1 subunit of the glycine receptor, and to investigate whether the putative "minor" form of hyperkeplexia consisting of an excessive startle response without stiffness, is based on the same genetic defect as the major form. DESIGN: A survey of various symptoms of hyperekplexia was performed in the Dutch pedigree. Linkage studies were performed for these symptoms. SETTING: Subjects were visited at home, and the genetic study was performed at University Hospital Leiden, (the Netherlands). PATIENTS: A history was taken from 76 subjects in the pedigree, and neurologic examinations were performed on 61 subjects from four generations of the pedigree. MAIN OUTCOME MEASURES: The main outcome measures were lod scores for markers on chromosome 5q for the major and minor forms of hyperekplexia and periodic leg movements during sleep. Mutations in the alpha 1 subunit of the glycine receptor were detected by screening the exons with denaturing gradient gel electrophoresis. RESULTS: Exaggerated startle responses were reported in 44 patients. The major form consisted of stiffness in addition to the excessive startle reaction and occurred in 28 subjects. Sixteen of 44 subjects had startle responses without stiffness, indicating the minor form. Linkage was found between markers CSF1-R, D5S209, and D5S119 and the disease locus for the major form, but not for the minor form. The alpha 1 subunit of the glycine receptor showed a G to A transition mutation in codon 271 for the major form, but not for the minor form. CONCLUSIONS: Linkage and an abnormal glycine receptor were found only in the major form of hyperekplexia. Recognition of a major form is based on additional stiffness. This is therefore the most important diagnostic symptom. The minor form is not a different expression of the same genetic defect and may represent a normal but pronounced startle response.