the science of heredity. Genetics is concerned primarily with understanding

biological properties that are transmitted from parent tooffspring. The subject matter of genetics includes hered-

ity, the molecular nature of the genetic material, the waysin which genes (which determine the characteristics of

organisms) control life functions, and the distributionand behavior of genes in populations.Genetics is central to biology because gene activityunderlies all life processes, from cell structure and function to reproduction.

Learning what genes are, how genes are transmitted from generation to generation

he principles of heredity were not understood untilthe mid-nineteenth century, when Gregor Mendel ana-

lyzed quantitatively the results of crossing pea plants thatvaried in easily observable characteristics. He published

his results, but their significance was not realized in hislifetime. Several years after his death, however, re-

searchers realized that Mendel had discovered fundamental principles of heredity

The structure of DNA was first described in 1953, andsince that time genetics has become one of the most excit-

ing and ground-breaking sciences. Our understanding ofgene structure and function has progressed rapidly since

molecular techniques were developed to clone or amplifygenes, and rapid methods for sequencing DNA became

available.

Research in genetics underwent a revolution in 1972,when Paul Berg constructed the first recombinant DNA

molecule in vitro, and in 1973, when Herbert Boyer andStanley Cohen cloned a recombinant DNA molecule for

the first time. The development by Kary Mullis in 1986of the polymerase chain reaction (PCR) to amplify

specific segments of DNA spawned another revolution.Recombinant DNA technology, PCR, and other molecular

technologies are leading to an ever-increasing number ofexciting discoveries that are furthering our knowledge of

basic biological functions and will lead to improvementsin the quality of human life.

In recent years, the sequencing of the genomes ofa large number of viruses and organisms has changed thescope of experiments performed by geneticists. For example, we can study a genome’s worth of genes now in oneexperiment, allowing us to obtain a more complete understanding of gene expression.

understanding of the abstract nature of genes (fromthe transmission genetics part) with the molecular nature

of genes (from the molecular genetics is one of the best approach

Classic Principles.

classic experiments, a number of which have led to discoveries

These experiments include:

•Griffith’s transformation experiment

•Avery and his colleagues’ transformation experiment

•Hershey and Chase’s bacteriophage experiment

•Meselson and Stahl’s DNA replication experiment

•Beadle and Tatum’s one-gene–one-enzyme hypothe-

sis experiments

•Mendel’s experiments on gene segregation

•Thomas Hunt Morgan’s experiments on gene linkage

•Seymour Benzer’s experiments on the fine structure

of the gene

•Jacob and Monod’s experiments on the lac operon

The Subdisciplines of Genetics

Geneticists often divide genetics into four major subdis-

ciplines:

1. Transmission genetics (sometimes called classical

genetics) is the subdiscipline dealing with how genes

and genetic traits are transmitted from generation to

generation and how genes recombine (exchange be-

tween chromosomes). Analyzing the pattern of trait

transmission in a human pedigree or in crosses of ex-

perimental organisms is an example of a transmis-

sion genetics study.

2. Molecular genetics is the subdiscipline dealing with

the molecular structure and function of genes. Ana-

lyzing the molecular events involved in the gene

control of cell division, or the regulation of expres-

sion of all the genes in a genome, are examples of

molecular genetics studies. Genomic analysis is part

of molecular genetics.

3. Population genetics is the subdiscipline that studies

heredity in groups of individuals for traits that are de-

termined by one or only a few genes. Analyzing the

frequency of a disease-causing gene in the human pop-

ulation is an example of a population genetics study.

4. Quantitative genetics also considers the heredity of

traits in groups of individuals, but the traits of concern

are determined by many genes simultaneously. Analyz-

ing the fruit weight and crop yield in agricultural

plants are examples of quantitative genetics studies.