Gene frequencies, variations

There are no circumstances for a gene with variation in Hardy-Weinberg equilibrium that will lead to equal numbers of individuals in each of the genotypic classes. Only in the case when allele frequencies are equal will the expected distribution be symmetrical. In such a case there will be equal numbers of the two homozygous classes (1/4 in each group), and 1/2 of the total sample will consist of heterozygotes. 

Gene frequencies and allelic mutations for ADH vary considerably and significant interpersonal and ethnic variations have been described. Furthermore, functional ADH is a dimer, usually of identical subunits but heterodimers are also possible and to date approximately 20 ADH isoenzymes are known. There are notable kinetic differences between the various functional ADH isoenzymes for example, Km values differ almost 1000-fold and Vmax by approximately 40-fold (see Table 6.4). These differences account, to some extent, for variation in alcohol tolerance between individuals. 

An essential step in understanding genetic variation is to measure it in populations. This is done by estimating genotype and gene frequencies. 

E. Louie, J. Ott, and J. Majewski, Nucleotide frequency variation across human genes. Genome Res. 13, 2594-2601 (2003). 

A fall in serum is commonly associated with hypokalemic periodic paralysis. Primary hypokalemic paralysis is usually first expressed in children and young adults. Paralytic attacks may fluctuate with remarkable frequency, and there is a common diurnal variation in severity, with weakness especially bad in the morning and evening. The condition has an autosomal dominant pattern of inheritance caused by an abnormality in or close to locus lql3. The gene product is unknown. 

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