When an individual who is homozygous dominant for the cleft chin gene (BB) has offspring with an individual who has a smooth chin (and is therefore homozygous recessive, bb), all of their children will invariably exhibit the cleft chin phenotype. This outcome is certain because every child will inherit one dominant 'B' allele from the first parent, resulting in a heterozygous (Bb) genotype.

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The inheritance of a cleft chin serves as a clear example of a monogenic trait influenced by dominant and recessive alleles. The allele for a cleft chin (represented as 'B') is dominant, while the allele for a smooth chin ('b') is recessive. Consequently, an individual with either a homozygous dominant (BB) or heterozygous (Bb) genotype will have a cleft chin. The smooth chin phenotype is only expressed in individuals with a homozygous recessive (bb) genotype.

Cleft Chin as an Example of a Monogenic Trait

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Inheritance of Cleft Chin from a Homozygous Dominant Parent

A Punnett square can be utilized to predict the genetic outcomes of a pairing between a heterozygous parent with a cleft chin (Bb) and a homozygous recessive parent with a smooth chin (bb). This particular cross produces four possible allele combinations for the offspring: two heterozygous (Bb) variants and two homozygous recessive (bb) variants. As a result, each child has an equal 50% probability of exhibiting the cleft chin trait or having a smooth chin.

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