Dominant trait

Dominant trait is a concept in genetics that refers to a characteristic which is expressed in an organism even when only one copy of the gene responsible for the trait is present. This is in contrast to a recessive trait, which requires two copies of the gene to be expressed. Dominant traits are a fundamental aspect of the inheritance patterns observed in many species, including humans.

Overview

In genetics, genes come in pairs. Organisms inherit one copy of each gene from each parent. Each variant of a gene is called an allele. When an individual has two different alleles for a specific trait, the allele that is expressed and determines the phenotype (observable characteristics) is termed dominant, while the allele that is masked or not expressed is termed recessive.

Mendelian Inheritance

The concept of dominant and recessive traits was first described by Gregor Mendel in the 19th century, through his work on pea plants. Mendel's laws of inheritance, including the law of segregation and the law of independent assortment, form the foundation of classical genetics. According to Mendel, the inheritance of each trait is determined by the units of inheritance (now known as genes), which are passed down from parents to offspring. Dominant traits manifest in the phenotype even when only one dominant allele is present (heterozygous condition), whereas recessive traits require the presence of two recessive alleles (homozygous condition).

Examples of Dominant Traits

Some examples of dominant traits in humans include:

• Dark hair
• Brown eyes
• Freckles
• Dimples
• A widow's peak hairline

It is important to note that the expression of traits is often more complex than simple dominance and can involve multiple genes (polygenic inheritance), incomplete dominance, codominance, and environmental factors.

Genetic Disorders and Dominant Traits

Some genetic disorders are caused by dominant alleles. These disorders can be passed to offspring when just one parent carries the dominant allele. Examples include:

• Huntington's disease
• Marfan syndrome
• Achondroplasia

Ethical Considerations

The study and manipulation of dominant traits, especially in the context of genetic disorders, raise ethical questions. Issues such as genetic testing, privacy, discrimination, and the potential for genetic engineering are areas of ongoing debate.

See Also

• Recessive trait
• Genotype
• Phenotype
• Mendelian inheritance
• Polygenic inheritance