Final answer:
Sudden, subtle changes in DNA passed on to offspring are mutations, which can occur spontaneously or due to environmental exposure. Mutations may alter gene function and are essential for evolution, with some such changes being heritable through epigenetics.
Step-by-step explanation:
Sudden, subtle changes in the DNA code passed on to offspring are known as mutations. These can arise spontaneously due to errors during DNA replication or as a result of environmental factors like radiation or exposure to toxic chemicals. Mutations affect the nucleotide sequence of genes, potentially altering the amino acid sequence of proteins, which can change the protein's function and structure. While mutations can lead to a variety of outcomes including harmful effects, they are also essential for evolution as they introduce new genetic material into a species. Some mutations can increase due to physical and chemical agents such as ultraviolet light and radioactive radiation. Over a human lifetime, epigenetic shifts, which are heritable changes in DNA that do not alter the DNA sequence itself but affect gene expression, can also be passed down to subsequent generations. These changes are often influenced by environmental exposures or lifestyle choices, potentially impacting the health and traits of descendants. It is important to acknowledge that most changes in DNA are corrected through repair mechanisms in cells; however, those that are not fixed become heritable mutations. Through the process of sexual reproduction, not only is genetic material rearranged but new genetic characteristics may emerge due to mutations, which are perpetuated when genes replicate during cell division.