How are traits passed from parents to children through genes?

Traits are passed from parents to children through genes, which are the functional units of heredity located on chromosomes. Humans typically have 46 chromosomes in their body cells, organized into 23 pairs—one set inherited from each parent.12

During the formation of sex cells, a process called meiosis reduces the chromosome number by half, creating haploid gametes that contain only one member of each chromosome pair. When these gametes fuse during fertilization, the offspring receives a complete set of paired chromosomes, combining genetic material from both parents.12

The specific forms of a gene are called alleles. An individual’s genotype is the combination of these alleles. How these traits appear, or the phenotype, often depends on the interaction between alleles. A dominant allele will typically override a recessive allele, meaning the recessive trait is only expressed if two copies of it are inherited. Through independent assortment and crossing over, parents produce a vast variety of unique genetic combinations in their offspring.34251