Heredity

Lore & Background

In humans, eye color is an example of an inherited characteristic, where an individual might inherit the 'brown-eye trait' from one parent. Inherited traits are controlled by genes, and the complete set of genes within an organism's genome is called its genotype. The complete set of observable traits of structure and behavior is called its phenotype, which arises from the interaction of the genotype with the environment. For example, suntanned skin derives from the interaction between a person's genotype and sunlight, and suntans are not passed on to children, though some people tan more easily due to differences in their genotype, such as those with albinism who do not tan at all.

Reader's Guide

Heritable traits are known to be passed from one generation to the next via DNA, a molecule that encodes genetic information. DNA is a long polymer incorporating four types of interchangeable bases, and the sequence of bases specifies genetic information. Before a cell divides through mitosis, DNA is copied so each resulting cell inherits the DNA sequence. A portion of a DNA molecule that specifies a single functional unit is called a gene, and different genes have different base sequences. Organisms inherit genetic material from their parents in the form of homologous chromosomes, containing a unique combination of DNA sequences that code for genes. The specific location of a DNA sequence within a chromosome is known as a locus, and different forms of the sequence at a locus are called alleles. DNA sequences can change through mutations, producing new alleles that may affect the trait the gene controls and alter the phenotype. However, most traits are more complex and controlled by multiple interacting genes. Recent findings have confirmed important examples of heritable changes not explained by direct agency of DNA, classed as epigenetic inheritance systems, such as DNA methylation, self-sustaining metabolic loops, gene silencing by RNA interference, and the three-dimensional conformation of proteins like prions. Heritability may also occur at larger scales, such as ecological inheritance through niche construction, where descendants inherit genes plus environmental characteristics generated by the ecological actions of ancestors.

Did You Know?

• The study of heredity in biology is called genetics.
• Suntanned skin is not inherited because it derives from the interaction between a person's genotype and sunlight.
• DNA sequences can change through mutations, producing new alleles that may alter the phenotype.
• Epigenetic inheritance systems include DNA methylation, gene silencing by RNA interference, and the three-dimensional conformation of proteins such as prions.