Biology – The roles of genes in determining the phenotype | e-Consult

The inheritance pattern of the Le and le alleles clearly demonstrates the principles of dominance and recessiveness. The Le allele is dominant because its presence, even in a single copy, results in the expression of the normal height phenotype. Conversely, the le allele is recessive because it only expresses the dwarf phenotype when two copies are present. This means that the recessive trait is only visible when the individual inherits two copies of the recessive allele.

In a pedigree chart, this inheritance pattern would be represented as follows:

• Affected individuals (dwarf plants) would be shown with a filled-in symbol, indicating they have at least one le allele.
• Unaffected individuals (normal height plants) would be shown with an unshaded symbol, indicating they have at least one Le allele.
• If an affected individual has unaffected parents, the affected individual must be heterozygous (Lele). This is because they must have inherited one le allele from each parent.
• If an affected individual has unaffected parents, the unaffected parents must both be carriers (heterozygous, Lele). This is because they can pass on the recessive le allele to their offspring without expressing the dwarf phenotype themselves.
• If an affected individual has affected parents, the affected individual must have inherited one le allele from each parent, meaning both parents must be carriers (Lele).

The consistent appearance of the dwarf phenotype in offspring with two affected parents, and the appearance of affected offspring with unaffected parents, are key indicators of autosomal recessive inheritance. The pedigree chart visually illustrates how the recessive allele can be passed down through generations, even if it is not expressed in every individual.