Comparison of Deficiency Alleles of the β-Globin and Factor VIII:C Genes: New Lessons from a Giant Gene
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Excerpt
Certain variables strongly influence the type of deficiency alleles observed at a locus, e.g., the size of the relevant gene, its chromosomal location, and whether deficiency alleles are under the influence of positive selection. In the case of the β-globin locus, the gene is small, the locus is autosomal in location, and β-thalassemia alleles are under positive selection in regions endemic for malaria that are populated by 50% of mankind. Thus, not all deficiency alleles of β-globin may be seen because (1) individuals carry two copies of the gene and (2) selection may result in the oldest deficiency mutations attaining the highest gene frequency.
In contrast, the factor VIII:C gene is quite large, and, because deficiency alleles are essentially X-linked lethals (until recently the reproductive fitness of hemophilia A patients was low), the mutations have a life of two to four generations in a stationary population (Haldane 1935) and nearly...
