How do different alleles affect an organism's characteristics?

Different alleles contribute to the variation in an organism's characteristics by determining specific traits through genetic coding.

Alleles are different versions of the same gene that are found at the same location (locus) on a chromosome. Each gene controls a particular characteristic in an organism, such as eye colour, hair colour, or height. The different alleles of a gene can lead to different expressions of that characteristic. For example, one allele of the gene for eye colour might code for blue eyes, while another allele might code for brown eyes.

The effect of an allele on an organism's characteristics can be dominant or recessive. A dominant allele will always express its characteristic, even if only one copy is present. A recessive allele will only express its characteristic if two copies are present, i.e., if the organism is homozygous for that allele. For example, if the allele for brown eyes is dominant and the allele for blue eyes is recessive, an organism with one brown-eye allele and one blue-eye allele will have brown eyes.

Furthermore, some characteristics are determined by multiple genes, each with their own alleles. This is known as polygenic inheritance. For instance, human height is influenced by many genes, each contributing a small amount to the overall height. This results in a wide range of possible heights, rather than just two or three possibilities.

In addition, the environment can also influence how an allele affects an organism's characteristics. This is known as gene-environment interaction. For example, a plant's height might be influenced by both its genetic makeup (the alleles it has for height) and its environment (how much sunlight and water it gets).

In conclusion, alleles play a crucial role in determining an organism's characteristics. They provide the genetic variation that underlies the diversity of life on Earth.