Alleles

An allele is a variant form of a gene. Genes encode the information needed for the synthesis of proteins, which perform a wide range of functions in the body. Each gene has a specific location on a chromosome, and each chromosome has a pair of alleles for a given gene. Alleles can be dominant or recessive, and they determine the traits or characteristics of an organism.

Key Concepts

• Gene: A unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
• Chromosome: A thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
• Dominant Allele: An allele that is fully expressed in the phenotype of a heterozygote.
• Recessive Allele: An allele that is masked when a dominant allele is present.

Mendelian Genetics

Alleles follow the principles of Mendelian genetics, which describe the inheritance of traits from one generation to the next. According to these principles, each organism has two alleles for a given gene, one inherited from each parent. These alleles can be the same (homozygous) or different (heterozygous).

Genotype and Phenotype

The combination of alleles an organism possesses is called its genotype, while the observable traits that result from the genotype are called the phenotype. For example, in the case of flower color in pea plants, the genotype may be homozygous dominant (RR), homozygous recessive (rr), or heterozygous (Rr), while the phenotype may be red, white, or a combination of both colors.

Study Tips

When studying alleles, it's important to understand the concepts of dominant and recessive alleles, as well as how they interact to determine the traits of an organism. Practice solving Punnett squares to predict the outcomes of genetic crosses, and familiarize yourself with terms such as homozygous, heterozygous, genotype, and phenotype. Additionally, explore real-life examples of genetic traits and their inheritance patterns to reinforce your understanding of alleles.