遗传是特征传递给后代的方式。基因决定了你的特质，比如你的身高，眼睛的颜色，头发的颜色。但是单个性状通常由许多基因决定，而不仅仅是一个。例如，单独的高度由超过400个基因决定。人类和其他多细胞生物在染色体的同一位点有两个等位基因。染色体是非常长的DNA链，包裹在称为组蛋白的特殊蛋白质周围。人类有46条染色体;每个父母都传递了23条染色体。因此，任何给定性状的表达将取决于两种信息来源。这两个来源是父系等位基因和母系等位基因。基因型是父母传递给个体的所有基因。但并非所有携带的基因都会被转化为可见的特征。个体具有的一组身体特征称为表型。个体的表型仅由表达的基因组成。例如，对于具有一个金色头发等位基因和一个棕色头发等位基因的个体。根据这些信息，我们知道他们的基因型包括金色头发和棕色头发。如果我们观察到个体有金发 – 换句话说，金发是表达的特征 – 那么我们知道他们的表型包括金发，但不是棕色头发。
Heredity is how traits are passed to offspring. Genes determine your traits, like how tall you are, what color your eyes are, and what color your hair is. But a single trait is usually determined by a number of genes, rather than just one. For example, height alone is determined by over 400 genes. Humans and other multicellular organisms have two alleles at the same site of a chromosome. Chromosomes are very long strands of DNA wrapped around special proteins called histones. Humans have 46 chromosomes; each parent passes on 23 of those chromosomes. Accordingly, the expression of any given trait would depend on two sources of information. These two sources are a paternal allele and a maternal allele. A genotype is all the genes passed onto an individual by their parents. But not all of the genes you carry end up being translated into visible traits. The set of physical characteristics an individual has is called a phenotype. An individual’s phenotype is made up exclusively of expressed genes. For example, take an individual who has one allele for blonde hair and one allele for brown hair. Based on this information, we know that their genotype includes blonde hair and brown hair. If we observe that the individual has blonde hair – in other words, blonde hair is the expressed trait – then we know that their phenotype includes includes blonde hair, but not brown hair.