Describe a dominant allele as an allele that is expressed if it is present in the genotype

Dominant Allele: Expression in the Genotype

A dominant allele is a specific type of allele that is expressed in the phenotype of an organism whenever it is present in the genotype. This means that even if an individual carries only one copy of the dominant allele, the associated trait will be visible in the organism’s physical appearance or characteristics.

1. Definition of Dominant Allele

• Dominant Allele: An allele that can mask the effect of a recessive allele when both are present in a heterozygous genotype. It is typically denoted by a capital letter (e.g., “A” for a dominant trait).

2. Expression of Dominant Alleles

The expression of a dominant allele occurs under the following conditions:

• Homozygous Dominant (AA): When an individual has two copies of the dominant allele, both alleles will express the dominant trait. For example, in pea plants, if “A” represents the allele for purple flowers, an individual with genotype AA will have purple flowers.
• Heterozygous (Aa): When an individual has one dominant allele and one recessive allele, the dominant trait will still be expressed. Using the same example, a plant with genotype Aa will also exhibit purple flowers due to the presence of the dominant allele.

3. Examples of Dominant Alleles

• Pea Plant Flower Color: In Mendel’s experiments, the purple flower color (P) is dominant over white flower color (p). Therefore, both PP and Pp genotypes will result in purple flowers.
• Human Traits: In humans, traits such as brown eyes are often controlled by dominant alleles. For instance, if “B” represents the brown eye allele and “b” represents blue eyes, individuals with genotypes BB or Bb will have brown eyes.

4. Importance of Dominant Alleles

Understanding dominant alleles is crucial for several reasons:

• Predicting Inheritance Patterns: Knowledge of dominant and recessive alleles helps predict how traits will be passed on to offspring, which is essential in fields like genetics and breeding.
• Genetic Disorders: Some genetic disorders are caused by dominant alleles. For example, Huntington’s disease is caused by a dominant mutation; individuals with just one copy of the mutated gene (Hh) will develop the disorder.