A gene is a hereditary unit that parents pass to their offspring, and they will determine the kind of characteristics the baby will have like will they be short or tall, have blue or brown eyes, will they have blond or black hair. The offspring will get different genes from its parents and it will therefore be genetically unique. Some traits or characteristics may be dominant over others. For example the mother has brown eyes and the father has blue eyes, so in this case eye color has two alleles (an allele is a specific version of a gene, in this case allele for blue eye color and an allele for brown eye color), and now the baby is born with brown eyes, so brown eye color was dominant over the blue eye color so that is the trait that we will see in the baby. The genetic is a lot more complex but this is a more simplified explanation of how offspring express certain traits from their parents.
