Alleles are passed from parents to offspring through sexual reproduction, where each parent contributes one allele for every gene. This means the offspring inherits two alleles per gene-one from the mother and one from the father

. During the formation of gametes (sperm and egg cells) through meiosis, the pairs of chromosomes separate so that each gamete receives only one allele of each gene. When fertilization occurs, the alleles from each parent combine to form the offspring’s genotype

. The combination of these alleles determines the offspring's traits. If both alleles are the same, the individual is homozygous for that gene; if they are different, the individual is heterozygous. Dominant alleles can mask the effect of recessive alleles, so the dominant trait is expressed in heterozygous individuals

. For example, if a child inherits a brown eye allele (dominant) from one parent and a blue eye allele (recessive) from the other, the child will have brown eyes. The random alignment and segregation of chromosomes during meiosis also means alleles for different genes can be assorted independently, leading to genetic diversity in offspring

. Moreover, some genes show co-dominance, where both alleles are expressed equally, such as the A and B alleles in blood groups

. In summary, alleles are passed from parents to offspring by each parent contributing one allele per gene through their gametes, which combine during fertilization to create the offspring’s unique genetic makeup