The cheetah is the poster
child for genetic diversity because it has the least
variability in its genes.
Most people think of DNA as a
crime-solving tool, but it is the medium that stores genes.
GLOSSARY OF TERMS:
Captive Management - The keeping
of animals in a manmade environment where decisions on how they live are made by
man. Squirrels in your back yard are in a manmade environment but are not
- The normal movement of offspring to new homes once they become mature enough
DNA - Special molecules made only
in living things that store genes. This works much as your computer hard disk stores files. It is an abbreviation
for "Deoxyribonucleic Acid".
- A gene that is "expressed." One that "wins" over a
recessive gene in determining how the offspring will develop.
Expression - When a gene has an
effect on how the offspring forms, that gene is said to be expressed.
Genetic Diversity - The amount of
inherited differences there are in a group of related individuals.
- When the two genes for a trait are different...one dominant and one
recessive...the trait is heterozygous.
- When the two genes for a trait are the same...both dominant or both
recessive...the trait is homozygous.
- When closely related animals have offspring together.
- A gene that is not "expressed" in the presence of a dominant gene
and only determines how the offspring will develop if it is
- A group of living things that can interact to produce offspring like
themselves. Tigers do not have lion cubs, and an eagle and owl cannot
interact to produce offspring like themselves.
Trait - A single difference in a
living thing caused by one gene. Eye color is a trait, but height and
learning ability are complex issues affected by several different genes.
Genetic diversity is a measure of how different a group of living things
are. It can refer to how different the puppies in the same litter are, or how
different all the world's lions are. The science behind genetic diversity
is complex, but the basic ideas are simple. Knowing something about
genetic diversity will help you understand how important it is.
Imagine that a tiger and tigress meet in the jungle to play with a game with
collector's cards. The tiger puts a card down with a trait on
it..."Fur Color." The tigress has to put down a card with the
same trait. The difference is, the male's card was for orange fur and was
marked "D" for Dominant. The female's card was for white fur and
was marked "R" for Recessive. A dominant trait card takes a
recessive trait card so the tiger scores that point. The tiger then puts
down a trait card for Night Vision. His card was for poor night vision and
is marked "R" for recessive. The tigress puts down a matching
trait card which is for excellent night vision and is marked "D" for
dominant. Dominant takes recessive so the tigress scores. They put
down pair after pair, until they go through the whole set of
The game looks pointless because the tiger and tigress don't keep the cards they
won. They both put their winnings in the same pile, which ends up with two
cards for every trait. This stack of cards becomes their offspring.
In fact, the tiger and tigress also started out that way, so their deck has two
cards for each trait. When they play a hand, they have to choose one of
each trait pair to put down. And since there are millions of different
traits in the deck and the chance that any tiger and tigress could pick the
exact same choices twice is nearly impossible. Though this cub will be
similar enough to its parents that it will definitely be a tiger--specifically a
Bengal tiger--it will also be different from all other tigers in the
world. But just how different is what genetic diversity is all
about. Good genetic diversity is the key to survival.
Under normal circumstances, when a tiger cub gets to be an adult, he or she
wanders far away from home and makes a new life somewhere else. That keeps
the game fresh and the tigers genetically diverse. Inbreeding occurs when
dispersal is not possible, and closely related tigers have offspring. For
trait after trait, it becomes more likely that neither parent will play a
dominant card. Recessive cards from both parents match up more frequently,
and rarely seen traits--some of them very unhealthy--become common. Many
inbred cubs die before they are born, and those who live may be weak or
ill. The problem is so serious that a zoo in Kansas may send their tiger
to California and their tigress to Florida to find mates rather than let them
breed with each other. If a large number of tigers is broken into small
groups, or the total number of tigers goes down, inbreeding happens more
often. Both problems are happening now to tigers and many other endangered
THE ONE STRIKE RULE:
If genetic diversity drops dangerously low, all members of the same species are
susceptible to the same diseases and prone to the same health conditions.
One disease could wipe out most--or all--of the species. It has happened
before and it can happen again.
HOW TO HELP:
The way new traits appear--mutation--is an extremely slow process. For all
practical purposes the traits that exist today are all we have to work with if
we are to preserve genetic diversity. Protecting tigers and their habitat,
reducing barriers to dispersal that cut habitat into small segments (roads,
fields, fences), and careful management of captive animals can all help preserve
genetic diversity. For some animals that are at extreme risk,
captive management may be their best--or only--hope of survival. That
makes learning the needs of captive endangered animals a high priority for
researchers. Cheetahs, for instance, do not breed well in captivity.
Certain conditions must be met beyond food and shelter for cheetahs to form a
self-sustaining population. Making a life for these animals--one that both
safe and truly worth living--is a difficult challenge but one we must meet.