Biology Now, 2e

118 ■ CHAPTER 07 Patterns of Inheritance

GENETICSGENETICS

G

ordon Lark’s best friend was dying. Soft

and shaggy, with tousled black hair,

Georgie hadn’t left Lark’s side in 10

years, since his daughter had first purchased

Georgie as a puppy from two kids by the side of

the road. But as she aged, Georgie had become

ill with Addison’s disease, a disorder in which

her body’s immune system began to attack and

destroy her own tissues. Georgie passed away

in 1996.

Lark, a scientist at the University of Utah in

Salt Lake City, was heartbroken. To help heal the

wound, he decided to adopt another dog of the

same breed—a Portuguese water dog (PWD),

named for its history of helping Portuguese

fishermen with their work (Figure 7.1). He

contacted Karen Miller, a PWD breeder on a

farm in rural New York. As part of the owner

screening process, Miller asked Lark about his

profession. “I said I was a soybean geneticist,”

Lark recalls, “but all she heard was ‘blah, blah,

genetics, blah, blah.’ And she got really excited.”

As a breeder, Miller was keenly interested

in how dogs inherit characteristics from their

parents, so Miller and Lark began talking by

phone each week about genetics. When it came

time to pick up his new puppy, Mopsa, Lark

requested the bill. But Miller didn’t want Lark’s

money. She had something else in mind: she gave

him Mopsa free of charge, in the hope that Lark

would start researching dog genetics. “That’s

silly,” Lark told her. He wasn’t a dog researcher.

Lark had spent a career studying the genetic

traits of bacteria and soybeans.

A genetic trait is any inherited characteristic

of an organism that can be observed or detected

in some manner. Some genetic traits are invari-

ant, meaning they are the same in all individu-

als of the species. All soybeans, for example, have

pods that contain seeds. Other genetic traits are

variable; for example, soybean seeds occur in

various sizes and colors, including black, brown,

and green.

Apart from his love for canines, Lark wasn’t

intimately familiar with dogs’ physical and

biochemical traits. Physical traits, such as

the shape of a dog’s face, are easy to observe.

Biochemical traits, on the other hand, such

as a dog’s susceptibility to Addison’s disease,

are often more difficult to observe. It is easy to

collect physical and biochemical information

from a field of soybeans but far more difficult to

collect it from domesticated animals in homes

all over the country. And to study dogs, Lark

would also need data on behavioral traits,

such as shyness and extroversion—factors he

didn’t have to take into account with soybeans.

All of these traits—physical, biochemical, and

behavioral—are influenced by genes.

Getting to the

Genes

A gene is the basic unit of information affect-

ing a genetic trait. At the molecular level,

a gene consists of a stretch of DNA on a

chromosome—a threadlike molecule, made

of DNA and proteins, that is found in the

nucleus of a eukaryotic cell (Figure 7.2). A

gene contains the information, or “code,” for

a specific protein; the protein then causes

or contributes to a particular genetic trait.

To study PWD traits, Lark would need dog

DNA, which can be obtained from blood or

saliva. Once he had that DNA, he could begin

to search for alleles—different versions of a

given gene—and link them to genetic traits.

Alleles of a gene arise by mutation, which is

any change in the DNA that makes up a gene

Figure 7.1

A Portuguese Water Dog