Genes and Alleles

Alleles

• Alleles are different forms of a gene that exist at a specific locus on a chromosome.
• Each individual carries two alleles for each gene, one inherited from each parent.

Genes and Chromosomes

• Genes are segments of DNA that code for proteins and determine traits, while chromosomes are structures that package and organize DNA within the cell.
• Humans have 23 pairs of chromosomes, with each pair being composed of one chromosome from each parent containing multiple genes.

Inheritance of Alleles

• For each gene, individuals inherit two alleles, one from each parent.
• This means an individual receives one allele from their mother and one from their father for every gene.

Genotype vs. Phenotype

• Genotype refers to the genetic constitution of an organism, encompassing both dominant and recessive alleles present.
• Phenotype is the observable physical or biochemical characteristics of an organism, which result from the interaction of the genotype with the environment.

Recessive Allele

• A recessive allele is one that does not manifest in the phenotype unless two copies are present (homozygous state).
• These alleles can be masked by dominant alleles, meaning their effects are only seen when paired with another recessive allele.

Dominant Allele

• A dominant allele is one that expresses its phenotype even when only one copy is present (heterozygous state).
• Dominant alleles can mask the effects of recessive alleles, influencing the organism's traits even if paired with a recessive allele.