Biology Now, 2e

Battling Resistance ■ 225

of the members of this rebounded population

are incredibly similar genetically, because of the

limited variety of alleles present in the original

six individuals. In an effort to restore gene flow

to the population, in 1995 researchers released

eight female Texas cougars, close genetic cousins

to the Florida panthers, into the panthers’ habi-

tat. Five of those females produced eight litters

of kittens—more genetically diverse, stronger,

and longer-lived than their fathers.

The founder effect occurs when a small

group of individuals establishes a new population

isolated from its original, larger population. For

example, in South Africa a population of people

called Afrikaners descended primarily from a

few Dutch colonists (Figure 12.16). Today, the

Afrikaner population has an unusually high

frequency of the allele that causes Huntington

disease because those original colonists by chance

carried the allele when they settled in the area.

After Vancomycin

When the initial case of VRSA popped up back

in 2002, the patient’s foot was carefully treated

with an old topical drug that is rarely used

today. The only other options were one or two

the founder effect. A genetic bottleneck is a

drop in the size of a population, for at least one

generation, that causes a loss of genetic varia-

tion (Figure 12.14). A genetic bottleneck can

threaten the survival of a population.

In the 1970s, for example, the population of the

endangered Florida panther plummeted because

of hunting and habitat destruction. The species

barely escaped extinction. At one point, experts

believed that only six wild individuals in the whole

species were still alive. This rapid population

reduction created a genetic bottleneck in which

an estimated half of the genetic variation within

the species was lost, and severe inbreeding among

the individuals that were left resulted in mala-

dies including low sperm counts and abnormally

shaped sperm in male panthers (Figure 12.15).

Thankfully, panther numbers have increased

to about 80–100 individuals in recent years, in

part because of captive breeding programs. Most

Normal panther sperm

Abnormal panther sperm

Figure 12.15

Abnormally shaped sperm in the rare

Florida panther

Florida panthers have more abnormal sperm than

do panthers from other populations—a possible

effect of a genetic bottleneck promoting the

increase of harmful alleles in the Florida panther

population.

Figure 12.16

Early Dutch colonists in South Africa