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.  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 traits.   

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.  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.  

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 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.

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