Science, Tech, Math › Science Gene vs. Allele: What’s the Difference? Share Flipboard Email Print Anthony Lee / Getty Images Science Biology Genetics Basics Cell Biology Organisms Anatomy Physiology Botany Ecology Chemistry Physics Geology Astronomy Weather & Climate By Omina Gohar is a science writer. She currently writes for Nature Middle East, the regional publication of Nature. our editorial process Omnia Gohar Updated January 06, 2020 A gene is a portion of DNA that determines a trait. A trait is a characteristic, or a feature, passed from one generation to another, like height or eye color. Genes come in multiple forms or versions. Each of these forms is called an allele. For example, the gene responsible for the hair color trait has many alleles: an allele for brown hair, an allele for blonde hair, an allele for red hair, and so on. Gene Allele Definition A gene is a portion of DNA that determines a certain trait. An allele is a specific form of a gene. Function Genes are responsible for the expression of traits. Alleles are responsible for the variations in which a given trait can be expressed. Pairing Genes do not occur in pairs. Alleles occur in pairs. Examples Eye color, hair color, hairline shape Blue eyes, blonde hair, V-shaped hairline Function Genes govern the traits of an organism. They do so by acting as instructions to make proteins. Proteins are the diverse molecules that play many critical roles in our bodies, such as producing hormones and creating antibodies. Humans have two copies (or alleles) of each gene, one inherited from each parent. Alleles play a significant role in shaping each human’s individual features. Alleles are versions of the same gene with slight variations in their sequence of DNA bases. These small differences among alleles of the same gene contribute to each person’s unique characteristics. Heredity Heredity is how traits are passed to offspring. Genes determine your traits, like how tall you are, what color your eyes are, and what color your hair is. But a single trait is usually determined by a number of genes, rather than just one. For example, height alone is determined by over 400 genes. Humans and other multicellular organisms have two alleles at the same site on a chromosome. Chromosomes are very long strands of DNA wrapped around special proteins called histones. Humans have 46 chromosomes; each parent passes on 23 of those chromosomes. Accordingly, the expression of any given trait would depend on two sources of information. These two sources are a paternal allele and a maternal allele. Genotypes and Phenotypes A genotype is all the genes passed onto an individual by their parents. But not all of the genes you carry end up being translated into visible traits. The set of physical characteristics an individual has is called a phenotype. An individual’s phenotype is made up exclusively of expressed genes. For example, take an individual who has one allele for blonde hair and one allele for brown hair. Based on this information, we know that their genotype includes blonde hair and brown hair. If we observe that the individual has blonde hair – in other words, blonde hair is the expressed trait – then we know that their phenotype includes blonde hair, but not brown hair. Dominant and Recessive Traits Genotypes can be either homozygous or heterozygous. When the two inherited alleles for a given gene are identical, this specific gene is called homozygous. Alternatively, when the two genes are different, the gene is said to be heterozygous. Dominant traits require the presence of only one allele in order for the given trait to be expressed. Recessive traits can only be expressed if the genotype is homozygous. For example, a V-shaped hairline is a dominant trait, while a straight hairline is recessive. In order to have a straight hairline, both hairline alleles need to be straight hairlines. However, in order to have a V-shaped hairline, only one of the two hairline alleles need to be V-shaped. Heterozygous Traits Monohybrid Cross: A Genetics Definition Sex-Linked Traits and Disorders What Are Traits? A Genetics Definition of Heterozygous Genes, Traits and Mendel's Law of Segregation Genes and Genetic Inheritance Dihybrid Cross in Genetics Probability and Punnett Squares in Genetics Genotype vs Phenotype Phenotype: How a Gene Is Expressed As a Physical Trait What Is Genetic Dominance and How Does It Work? What Does Homozygous Mean in Genetics? Introduction to Mendel's Law of Independent Assortment Probabilities for Dihybrid Crosses in Genetics How Do Alleles Determine Traits in Genetics?