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INTRODUCTION:
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.
TRAITS:
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. In genetics, the
trait that "scores" is said to be expressed. The outcome of
dominant orange fur against recessive white fur would be orange (not some sort
of whitish orange--winner takes all). Traits are the smallest details in
the instructions to build an animal or plant. How tall you are or how
smart you are depends on many different things, including the way you are
raised, so those are not really traits. Your eye color, skin color and any
allergies you may have are traits. The tiger and tigress put
down pair after pair of traits, covering every detail from nose to tail tip
until they go through the whole deck. If this were a real card game it
would take a very long time to play. There are nearly 30,000 distinct
traits, quite a hard deck to shuffle!
NEW COMBINATIONS:
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, whose
appearance will depend on which card of each trait is the dominant one.
In fact, the tiger and tigress also started out that way, so their deck also has two
cards for each trait. When they play a hand, they have to choose one of
each trait pair at random to put down. And since there are tens of
thousands of
different traits in the deck, 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.
INBREEDING:
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
species.
THE ONE STRIKE RULE:
If genetic diversity drops dangerously low, all members of the same species are
prone to the same health problems.
One disease could wipe out most--or all--of the species. It has happened
before and it can happen again.
DEGREES OF DANGER:
People are used to hearing the term "endangered species" used a lot, sometimes
incorrectly. There are actually two different degrees of concern for
species. Threatened species are those whose populations are falling
steadily and need to be watched closely. Endangered species are
those in immediate danger of becoming extinct. Sometimes the terms refer
to how the species is doing in a certain place. The gray wolf is
threatened in Minnesota but endangered in Wyoming. Black Footed Ferrets
are endangered everywhere.
HOW TO HELP:
New traits appear at a very slow rate. 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.
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