Genes are segments of DNA that contain the instructions for building and maintaining an organism. Each gene resides at a specific locus (location) on a chromosome.
Alleles are variations in the DNA sequence at a particular locus. These variations can lead to differences in the traits they code for.
Key Concepts:
* Diploid organisms inherit two copies of each gene, one from each parent. These two copies may be the same allele (homozygous) or different alleles (heterozygous).
* Dominant alleles mask the expression of recessive alleles when they are present together.
* Recessive alleles are only expressed when two copies of the recessive allele are present.
* Genotype refers to the combination of alleles an individual possesses.
* Phenotype refers to the observable traits resulting from the genotype.
Example:
Consider the gene for eye color. There are two alleles: brown (B) and blue (b).
* BB genotype (homozygous dominant): Brown eyes
* Bb genotype (heterozygous): Brown eyes (brown allele is dominant)
* bb genotype (homozygous recessive): Blue eyes
Significance of Alleles:
* Genetic diversity: Alleles contribute to the genetic diversity within a population.
* Evolution: Natural selection acts on the variation in alleles, leading to evolutionary changes.
* Inheritance: Alleles are passed down from parents to offspring, determining traits.
* Genetic disorders: Some alleles are associated with genetic disorders.
In summary, alleles are the building blocks of genetic variation, contributing to the diversity of traits observed in living organisms.
