For some alleles there is no dominance, and phenotype results from both alleles being expressed or from a blending of phenotype. The expression is an "average" or combination of the two traits. In humans, for example, there is a specific gene that codes for the protein that determines an individual's major blood type, which can be A, B, AB, or O. This is determined by a single gene that has three alleles that can code for:. While there are three alleles, each of us has just two of them, so the possible combinations and the resulting blood types are those shown in the table below.
All Rights Reserved. Date last modified: February 2, Created by Wayne W. DNA, Genetics, and Evolution. Contents All Modules. Allele frequency dynamics in a pedigreed natural population. National Library of Medicine. Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data.
We and our partners process data to: Actively scan device characteristics for identification. I Accept Show Purposes. Dominant and Recessive Traits Brown eye color is a dominant trait, while blue eye color is a recessive trait. Was this page helpful? Thanks for your feedback! Sign Up. What are your concerns? Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Related Articles. What Is Congenital Muscular Dystrophy? How to Understand Heterozygous vs. Homozygous Genes. Causes and Risk Factors of Xeroderma Pigmentosum. What Is the Rarest Eye Color? In a simplified model, we will assume that there is only one gene that encodes for eye color although there are multiple genes involved in most physical traits.
Blue, green, brown, and hazel eyes are each encoded by unique alleles of said gene. When humans procreate, the child receives 23 chromosomes long strands of DNA from each parent. Each matching chromosome pair contains the same set of genes, with unique genes located at certain spots known as the gene locus. This inheritance means that individuals have two gene copies for a given trait, one inherited from their mother and the other from their father. These are known as maternal alleles and paternal alleles.
It is how these alleles interact that is responsible for unique characteristics. But not all gene variations will be expressed. For instance, you might have one allele for brown eyes and another for blue eyes, but you will not therefore have one blue and one brown eye. Individuals do not display the characteristics encoded on each matching pair of genes.
Instead, the genes that are expressed result in the phenotype , which is how genes are expressed in observable characteristics. How does the body know which alleles to express? In these butterflies, temperature and light can influence gene expression. Consequently, wing color and pattern can vary depending on the season during which a butterfly is born. The top row of Figure 2 shows examples of three different butterfly species.
The bottom row shows butterflies from the same three species, but these individuals were born under different temperature and light conditions than those in the top row. How can this happen? The differences in wing colors and patterns of butterflies of the same species reflect the underlying genetic variability within a population.
Even though each butterfly within a species has the potential to develop the wide variety of colors and patterns shown above, its environment influences the phenotypic expression of its genetic characteristics. The gene pool of each species, therefore, contains a collection of many different alleles whose phenotype may or may not be observable.
Can gene pools vary within populations? The factors that affect the composition of the gene pool are shaped both by the physical environment and by time. Consequently, the definition of populations can be refined to include groups of organisms whose genetic makeup can change over time, and groups of organisms that tend to interbreed. Key Questions How can mutation cause genetic variation? Key Concepts genetic variation species. Topic rooms within Genetics Close. No topic rooms are there.
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