Pedigree Analysis of Genetic Marker co-occurence

    The pedigree in (A) shows the co-occurence of a disease phenotype [filled symbols] with genetic variation at locus M starting with an affected woman in the first generation. The occurence of the disease in each of three successive generations suggests autosomal dominant inheritance: only one allele is required to produce the condition, and the condition is more or less equally frequent in males and females. Genotyping of the mother shows she is heterozygous for two alleles (M1/M2).

    The analysis in (B) tests two alternative hypothesis, that either allele M1 or M2 is genetically linked to the disease state (Hypotheses 1 and 2, respectively).Three offspring with M1 are affected, and two of three children with M2 are unaffected while the third is affected. Hypothesis 1 best explains the distribution, if a single recombination event has unlinked the M1 marker from the disease phenotype (RF = 1/6 = 0.167]. Hypothesis 2 would require five such events

   In part (C), Hypothesis 1 means that the deceased maternal grandmother would be expected to have had allele M1, concordant with her disease state.Genetic analysis of tissue on decades-old biopsy slides can identify the presence of absence of the M1 allele. In the example, the woman is heterozygous for M1. Genotyping the M locus may be useful in predicting occurence of the disease in other family members

Figure ©2012 TA Brown, Introduction to Genetics (1st ed.); additional text ©2014 by Steven M. Carr