Numerous advances in genetics are being made today, and genetics remains at the forefront of biological research. New, rapid methods for sequencing DNA are being used to sequence the genomes of numerous species, from strawberries to butterflies to elephants. Recently, these methods were used to reconstruct the entire genome of an unborn fetus from fetal DNA circulating in the mother’s blood, providing the potential for noninvasive prenatal genetic testing. Analysis of DNA from ancient bones demonstrates that several different species of humans roamed Earth as recently as 30,000 years ago. Powerful modern genetic techniques have been used to identify genes that influence agriculturally important characteristics, such as size in cattle, domestication in chickens, speed in racehorses, and leaf shape in corn. DNA analysis is now routinely used to identify and convict criminals or prove the innocence of suspects.

The power of new methods to identify and analyze genes is illustrated by genetic studies of myocardial infarction (heart attack) in humans. Physicians have long recognized that heart attacks run in families, but finding specific genes that contribute to an increased risk of heart attack has, until recently, been difficult. An international team of geneticists examined the DNA of 26,000 people in 10 countries for single nucleotide differences in their DNA (called single-nucleotide polymorphisms, or SNPs) that might be associated with an increased risk of heart attack. This and other similar studies identified several new genes that affect the risk of coronary artery disease and early heart attacks. These findings may make it possible to identify people who are predisposed to heart attack, allowing early intervention that might prevent the attacks. Analyses of SNPs are helping to locate genes that affect all types of traits, from eye color and height to glaucoma and cancer.

Information about sequence differences among organisms is also a source of new insights about evolution. For example, scientists analyzed DNA sequences at 26 genes to construct a comprehensive evolutionary tree of mammals. The tree revealed many interesting features of mammalian evolution; for instance, marine mammals (whales, dolphins, and porpoises) are most closely related to hippos.

11

In recent years, scientists have discovered that alterations to DNA and chromosome structure that do not involve the base sequence of the DNA play an important role in gene expression. These alterations, called epigenetic changes, affect our appearance, behavior, and health, and they are currently the focus of intense research. Other studies demonstrate that RNA is a key player in many aspects of gene function. The discovery in the late 1990s of tiny RNA molecules called small interfering RNAs and microRNAs led to the recognition that these molecules play central roles in gene expression and development. New genetic microchips that simultaneously analyze thousands of RNA molecules are providing information about the activities of thousands of genes in a given cell, allowing a detailed picture of how cells respond to external signals, environmental stresses, and diseases such as cancer. In the field of proteomics, powerful computer programs are being used to model the structure and function of proteins from DNA-sequence information. All this information provides us with a better understanding of numerous biological processes and evolutionary relationships. The flood of new genetic information, which requires the continuous development of sophisticated computer programs to store, retrieve, compare, and analyze genetic data, has given rise to the field of bioinformatics, a merging of molecular biology and computer science.

As the cost of sequencing decreases, the focus of DNA-sequencing efforts will shift from the genomes of different species to individual differences within species. In the not-too-distant future, each person will probably possess a copy of his or her entire genome sequence, which can be used to help assess the risk of acquiring various diseases and to tailor their treatment should they arise. The use of genetics in agriculture will continue to improve the productivity of domestic crops and animals, helping to feed the future world population. This ever-widening scope of genetics raises significant ethical, social, and economic issues.

This brief overview of the history of genetics is not intended to be comprehensive; rather, it is designed to provide a sense of the accelerating pace of advances in genetics. In the chapters to come, we will learn more about the experiments and the scientists who helped shape the discipline of genetics.