What are the general effects of inbreeding

From: Subject: What are the general effects of inbreeding Date: Mon, 19 Apr 2004 20:55:05 -0500 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_0000_01C42650.9770AE80"; type="text/html" X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0000_01C42650.9770AE80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Location: http://cc.ysu.edu/~helorime/inbred.html What are the general effects of inbreeding =20

Inbreeding and it's General=20 Effects

=20

=20 Mammals, most other animals, and higher plants as well, have = evolved=20 mechanisms to avoid inbreeding of any sort. Some, like sweet = cherries,=20 have even evolved elaborate biochemical mechanism to ensure that = their=20 flowers can not be fertilized by themselves or by very genetically = similar=20 individuals.=20

Most pack = animals=20 (like lions, primates, and dogs),kick young males out of the pack = so as to=20 prevent them from mating with female relatives. Humans have very = strong=20 taboos against mating with relatives. Even fruit-flies apparently = have a=20 sensing mechanism to avoid too close of inbreeding, even in a = closed=20 population they maintain more genetic diversity than they ought to = by=20 random mating.=20

Why do = living things=20 avoid inbreeding? Because in general, it is quite bad for a = population or=20 an organism to be very inbred. There is a well studied, although = only=20 partially understood phenomenon called inbreeding=20 depression.=20

= Inbreeding depression=20 is thought to be caused primarily by the collection of a multitude = of=20 deleterious mutations, few in themselves fatal, but all = diminishing=20 fitness. Normally, in an outbreeding population these alleles = would be=20 selected against, hidden, or corrected by the presence of good = alleles=20 (versions of genes) in the population.=20

We = generally think=20 that mutations arise only once in a great while. That is certainly = true=20 for individual genes and specific kinds of mutations. However = scientists=20 have measured mutation rates in humans, chimpanzees and gorillas = and=20 discovered that there are roughly 4.2 = mutations/individual/generation that=20 affect the actual final proteins encoded by the genes. (A, = Eyre-Walker, P.=20 D. Keightly, Nature 397:344-347. 1999). Of these mutations about = 1.5 are=20 deleterious, in other words would cause harm to the animal if they = were=20 homozygous. The scientists who performed this analysis suspect = that their=20 numbers are actually artificially low for a variety of valid = reasons, and=20 estimate that the actual number may be closer to 3 deleterious = mutations=20 per individual per generation.=20

So how = come we don't=20 all have tons of genetic diseases? The answer to that is fairly = simple,=20 sexual reproduction, and the shuffling of alleles of genes that = occurs=20 when two unrelated individuals mate.=20

When that = shuffling=20 can't happen because both parents already have mostly the same = alleles,=20 the result will be inbreeding depression, if not in a given = litter, then=20 in a few more generations of such breedings.=20

= Inbreeding depression=20 encompasses a wide variety of physical and health defects. Any = given=20 inbred animal generally has several, but not all, of these = defects. These=20 defects include:=20

&nb= sp;=20 Elevated incidence of recessive genetic=20 diseases=20

&nb= sp;=20 Reduced fertility both in litter size and in sperm=20 viability=20

&nb= sp;=20 Increased congenital defects such as cryptorchidism, heart = defects, cleft=20 palates.=20

&nb= sp;=20 Fluctuating assymetry (such as crooked faces, or uneven eye = placement and=20 size).=20

&nb= sp;=20 Lower birthweight=20

&nb= sp;=20 Higher neonatal mortality=20

&nb= sp;=20 Slower growth rate=20

&nb= sp;=20 Smaller adult size, and=20

&nb= sp; =20 Loss of immune system = function.

Can you at least = eliminate=20 specific genetic defects through inbreeding? (next)=20

back to:
          &nb= sp; Inbreeding= =20
          &nb= sp; Feline = Genetics=20
          &nb= sp; Synergy=20 homepage
          &nb= sp; Dr. Lorimer's Academic=20 Pages
=20

@Heather E. Lorimer, = Ph.D.=20

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