OM aybe you know someone who is the spitting image of some one else in the family This is thanks to genes Genetics the study of genes involves far more than family resem blances though A century after pioneering experiments revealed the role of genes in heredity scientists learned that genetic engineering the manipulation of genes can be an important tool in medicine and agriculture This book provides an overview of the history of genetics It offers an expla nation of how genes work as well as what can happen when genetic defects occur It also explores some up and coming tech nologies that harness the power of genetic engineering People have known since ancient times that particular traits can be passed along from parent to offspring How this occurred was long a mystery though Scientists pro VI posed many theories through the years One prevailing theory of the early 1800s was My blending inheritance which held that an organism's heritable traits are a combination of those in the parents Charles Darwin used this theory to support his own theory of nat ural
INTRODUCTION In the mid 1800s an Austrian monk named Gregor Mendel became the first person to show scientifically how specific characteristics pass from one generation to the next Experimenting with garden peas Mendel deduced that distinct hereditary units that passed from parent to offspring determined how traits were inherited These units eventually became known as genes By studying the humble pea plant Mendel was able to demonstrate fundamental genetic principles such as segregation and indepen dent assortment Biologists who followed in Mendel's footsteps discovered how genes and chro mosomes were related and eventually the role of DNA In the early 1900s Thomas H Morgan determined that genes are found on chromosomes with each gene located at a specific site and that patterns of inheri tance are based on the position of genes on each chromosome Morgan also verified that genes near one another on the same chromo Some are apt to be inherited together Chromosomes are a collection of DNA and protein found in every living thing Each gene has a specific place on a specific chro mosome Most organisms have two sets of
A CLOSER LOOK AT GENES AND GENETIC ENGINEERING In the United States most commercially grown corn is genetically modified Adam Gault OJO Images Getty Images
INTRODUCTION I paired chromosomes with one set inher ited from each parent When cells reproduce chromosomes carry genetic information from the parent cell to the newly produced daughter cells Most cells reproduce through a process called mito sis In mitosis One cell divides into two exact copies of itself But gametes sex cells duplicate through mei osis which involves two cell divisions The first division produces two daughter cells with a full set of chromosomes In the second division however the chromo somes do not duplicate resulting in four daugh ter cells with only half as many chromosomes The full set of chromo somes is restored when
