Biology Now, 2e

A Deadly Inheritance ■ 137

members over two or more generations of a

family’s medical history (Figure 8.2). Pedigrees

provide scientists with a way to analyze infor-

mation in order to learn about the inheritance

of a particular genetic trait or disorder. Aldrich

found that 16 male infants in the family, but no

females, had died of the syndrome (Figure 8.3).

Because of the “remarkable family history,” as

he described it, Aldrich concluded, like Wiskott,

that the illness was a genetic disorder, caused by

a mutation passed down from parent to child.

Genetic disorders can be caused by mutations in

Painful Pedigree

Tw e n t y y e a r s a f t e r W i s k o t t d e s c r i b e d t h e fi r s t c a s e s

of the mysterious disease and determined that

it was inherited, an American pediatrician, Dr.

Robert Anderson Aldrich, solved the next piece of

the puzzle. Aldrich met a six-month-old boy with

anemia, bloody diarrhea, and general weakness.

After several emergency room visits, the baby died.

Aldrich sat down with the boy’s mother to review

possible causes. After an hour of asking questions,

he still had no idea what might have brought on

the illness. Finally, he asked about other relatives

who might have had a similar illness. The boy’s

grandmother, who had tagged along to the meet-

ing, exclaimed sadly, “Just like all the rest of them.”

Other male infants in the family, it turned out, had

died under similar circumstances.

Given that information, Aldrich worked

with the mother and grandmother to trace the

family’s history back six generations by draw-

ing a pedigree, a chart similar to a family tree

that shows genetic relationships among family

I

Female Male Unaffected

individual

Affected

individual

1 2

1 2 3 4 5 6

1 2 3 4

Generation

II

III

All geneticists who study human inheritance use a

standard set of symbols in pedigrees:

● Roman numerals identify different generations

● Circles represent females; squares represent males

● Open symbols (blue here) represent unaffected

individuals; filled symbols (red here) represent

affected individuals

● Numbers listed below the symbols identify

individuals of a given generation

Figure 8.2

Patterns of inheritance can be analyzed in family pedigrees

This cystic fibrosis pedigree shows six children (generation III), two of whom are affected with the

disease.

Q1: Which two children in this pedigree have cystic fibrosis? How do you know?

Q2: Does either parent of these two children have cystic fibrosis? If so, which one(s)? How do

you know?

Q3: Do any of the grandparents of these two children have cystic fibrosis? If so, which one(s)?

How do you know?

A medical doctor and cancer researcher, Christoph

Klein is now chair of pediatrics at the University

of Munich. In 2010, Klein began testing a new gene

therapy to treat young children with Wiskott-Aldrich

syndrome, a rare and life-threatening disease. The

therapy, though still experimental, has been very

successful.

CHRISTOPH KLEIN