Alleles

Alleles are alternative versions of the same gene that occupy corresponding positions (loci) on paired chromosomes. These variations emerged through mutation processes over time and play a fundamental role in genetic diversity and inheritance patterns.

Basic Concepts

Each diploid organism inherits two alleles for each gene, one from each parent. These paired alleles can be:

• Homozygous: When both alleles are identical
• Heterozygous: When the alleles are different

Expression Patterns

The interaction between alleles determines how genes are expressed:

1. Dominant Alleles

   • Override the effects of recessive alleles
   • Expressed in both homozygous and heterozygous conditions
   • Usually denoted with capital letters (e.g., "A")

2. Recessive Alleles

   • Only expressed when two copies are present
   • Hidden in heterozygous conditions
   • Usually denoted with lowercase letters (e.g., "a")

3. Codominant Alleles

   • Both alleles are fully expressed
   • Common in blood type determination
   • Neither allele is dominant over the other

Role in Evolution

Alleles are crucial for:

• Maintaining genetic diversity in populations
• Enabling natural selection processes
• Contributing to adaptation capabilities

Medical Significance

Understanding alleles is vital for:

• Tracking inherited diseases
• Predicting genetic disorder risks
• Developing targeted genetic therapy treatments

Population Genetics

The distribution and frequency of alleles in populations help scientists:

• Study gene flow between populations
• Track evolutionary changes
• Understand genetic drift effects

Alleles form the basis of Mendelian inheritance patterns and are fundamental to our understanding of how traits are passed between generations. Their study continues to reveal new insights into both human health and evolutionary biology.