Dinucleotide repeat polymorphism at the D21S168 locus

Genetic variation of microsatellite markers D1S117, D6S89, D11S35, APOC2, and D21S168 in the Spanish population

We have used PCR amplification to analyse the allele frequency, distribution and heterozygosity of 5 microsatellite markers (D1S117, D6S89, D11S35, APOC2, and D21S168), in a sample of 100 unrelated Spanish individuals. The loci tested exhibit wide allelic variability having 7-17 alleles, PIC (polymorphic information content) between 0.79 and 0.86, and heterozygosity between 0.81 and 0.86. D1S117 and D21S168 have unimodal distribution, APOC2 has 4 common alleles which account for 71% of the total variation, D11S35 has a bimodal distribution and D6S89 is trimodal. The allelic distribution observed for each locus is in agreement with slippage and mispairing as the main mechanisms involved in the evolution of microsatellite alleles. Multiplex amplification of loci D6S89 and APOC2 was possible due to their non-overlapping allele sizes. The rapidity with which microsatellites can be analysed, and the accurate determination of alleles, make these markers very powerful tools for genetic typing. The information obtained for loci D1S117, D6S89, D11S35, APOC2, and D21S168, provides a basis for their use for DNA typing and paternity analysis in the Spanish population.

Exclusion of two candidate pigment loci, c and b, part of chromosome 11p, and 33 random polymorphic markers as the locus for tyrosinase-positive oculocutaneous albinism

The locus for Tyrosinase-Positive Oculocutaneous Albinism (ty-pos OCA) has not yet been localised. The search for the ty-pos OCA locus has included a search for linkage to candidate pigment loci and a candidate chromosomal region, as well as a random search using highly polymorphic markers in 42 families, including 271 individuals of whom 79 are affected. The lod scores for the tyrosinase (TYR) locus (11q14-q21), homologous to the albino locus, c, in the mouse and the CAS2/TRP1 locus (9p22-pter), homologous to the brown locus, b, in the mouse were -5.89 and -7.22, respectively, at a recombination fraction of theta = 0.01, thus excluding them from being the ty-pos OCA locus. In the candidate chromosomal region, 11p, four loci (probes) were tested, SAA (pSAA82), CALC (pHC36), HBB (Gamma-globin haplotype) and an AC repeat polymorphism at the Wilm's Tumour locus (WT1). A portion of 11p was excluded with the following lod scores: pSAA82 lod = -2.05 at theta = 0.10; pHC36 lod = -3.87 at theta = 0.05; gamma-globin haplotype lod = -2.80 at theta = 0.10; and WT1 lod = -2.34 at theta = 0.10. Thirty-three polymorphic markers randomly distributed on 13 different chromosomes were all excluded from close linkage to ty-pos OCA.