Are hand spans inherited as a simple Mendelian pattern or as a polygenic or incomplete dominance pattern

Since there is a continuum of sizes for hand spans amongst individuals, the trait is a polygenetic trait.

In order to know how to answer the question, there must be a firm understanding of each term within the question. Each term is briefly described below.

1. Simple Mendelian inheritance involves two alleles per gene, which can be either dominant or recessive. An allele is one of two version of a gene that is found on the same loci of chromosomes. Dominant alleles are the “stronger” version of a gene, whereas recessive alleles are the “weaker”. Only one dominant allele needs to be present in order for an individual to display the dominant trait. However, two recessive alleles need to be present in order for an individual to display the recessive trait. Such traits will be either one of two phenotypes.


2. Polygenetic traits are traits that are influenced by more than one gene (“poly” = many). Therefore, such phenotypes may fall anywhere within a spectrum of possibilities.


3. Incomplete dominance also involves two alleles per gene for a phenotype. However, neither allele is dominant over the other. When the two different alleles are paired within a genotype, the result will be a blended phenotype.