studies show that inbreeding depression and ecological factors have an influence on survival. the florida panther population was reduced to about 30 animals, so inbreeding became a problem. several females were imported from texas and now the population is better off genetically. measures a measure of inbreeding of an individual a is the probability f(a) that both alleles in one locus are derived from the same allele in an ancestor. these two identical alleles that are both derived from a common ancestor are said to be identical by descent. this probability f(a) is called the "coefficient of inbreeding". another useful measure that describes the extent to which two individuals are related (say individuals a and b) is their coancestry coefficient f(a,b), which gives the probability that one randomly selected allele from a and another randomly selected allele from b are identical by descent. this is also denoted as the kinship coefficient between a and b. a particular case is the self-coancestry of individual a with itself, f(a,a), which is the probability that taking one random allele from a and then, independently and with replacement, another random allele also from a, both are identical by descent. since they can be identical by descent by sampling the same allele or by sampling both alleles that happen to be identical by descent, we have f(a,a) = 1/2 + f(a)/2. both the inbreeding and the coancestry coefficients can be defined for specific individuals or as average population values. they can be computed from genealogies or estimated from the population size and its breeding properties, but all methods assume no selection and are limited to neutral alleles. there are several methods to compute this percentage. the two main ways are the path method and the tabular method. typical coancestries between relatives are as follows: father/daughter or mother/son → 25% (1⁄4) brother/sister → 25% (1⁄4) grandfather/granddaughter or grandmother/grandson → 12.5% (1⁄8) half-brother/half-sister, double cousins → 12.5% (1⁄8) uncle/niece or aunt/nephew → 12.5% (1⁄8) great-grandfather/great-granddaughter or great-grandmother/great-grandson → 6.25% (1⁄16) half-uncle/niece or half-aunt/nephew → 6.25% (1⁄16) first cousins → 6.25% (1⁄16) animals wild animals few studies have found evidence of regular incest avoidance in mammals, but banded mongooses are an exception. banded mongoose females regularly mate with their fathers and brothers. bed bugs: north carolina state university found that bedbugs, in contrast to most other insects, tolerate incest and are able to genetically withstand the effects of inbreeding quite well. common fruit fly females prefer to mate with their own brothers over unrelated males. cottony cushion scales: 'it turns out that females in these hermaphrodite insects are not really fertilizing their eggs themselves, but instead are having this done by a parasitic tissue that infects them at birth,' says laura ross of oxford university's department of zoology. ‘it seems that this infectious tissue derives from left-over sperm from their father, who has found a sneaky way of having more children by mating with his daughters.' adactylidium: the single male offspring mite mates with all the daughters when they are still in the mother. the females, now impregnated, cut holes in their mother's body so that they can emerge. the male emerges as well, but does not look for food or new mates, and dies after a few hours. the females die at the age of 4 days, when their own offspring eat them alive from the inside. white tiger in gunma safari park domestic animals hereditary polycystic kidney disease is prevalent in the persian cat breed, affecting almost half the population in some countries. an intensive form of inbreeding where an individual s is mated to his daughter d1, granddaughter d2 and so on, in order to maximise the percentage of s's genes in the offspring. 87.5% of d3's genes would come from s, while d4 would receive 93.75% of their genes from s. breeding in domestic animals is primarily assortative breeding (see selective breeding). without the sorting of individuals by trait, a breed could not be established, nor could poor genetic material be removed. homozygosity is the case where similar or identical alleles combine to express a trait that is not otherwise expressed (recessiveness). inbreeding exposes recessive alleles through increasing homozygosity. breeders must avoid breeding from individuals that demonstrate either homozygosity or heterozygosity for disease causing alleles. the goal of preventing the transfer of deleterious alleles may be achieved by reproductive isolation, sterilization, or, in the extreme case, culling. culling is not strictly necessary if genetics are the only issue in hand. small animals such as cats and dogs may be sterilized, but in the case of large agricultural animals, such as cattle, culling is usually the only economic option. the issue of casual breeders who inbreed irresponsibly is discussed in the following quotation on cattle: meanwhile, milk production per cow per lactation increased from 17,444 lbs to 25,013 lbs from 1978 to 1998 for the holstein breed. mean breeding values for milk of holstein cows increased by 4,829 lbs during this period. high producing cows are increasingly difficult to breed and are subject to higher health costs than cows of lower genetic merit for production (cassell, 2001). intensive selection for higher yield has increased relationships among animals within breed and increased the rate of casual inbreeding. many of the traits that affect profitability in crosses of modern dairy breeds have not been studied in designed experiments. indeed, all crossbreeding research involving north american breeds and strains is very dated (mcallister, 2001) if it exists at all. the bbc produced two documentaries on dog inbreeding titled pedigree dogs exposed and pedigree dogs exposed: three years on that document the negative health consequences of excessive inbreeding. linebreeding linebreeding is a form of inbreeding. there is no clear distinction between the two terms, but linebreeding may encompass crosses between individuals and their descendants or two cousins. this method can be used to increase a particular animal's contribution to the population. while linebreeding is less likely to cause problems in the first generation than does inbreeding, over time, linebreeding can reduce the genetic diversity of a population and cause problems related to a too-small gene pool that may include an increased prevalence of genetic disorders and inbreeding depression. outcrossing outcrossing is where two unrelated individuals are crossed to produce progeny. in outcrossing, unless there is verifiable genetic information, one may find that all individuals are distantly related to an ancient progenitor. if the trait carries throughout a population, all individuals can have this trait. this is called the founder effect. in the well established breeds, that are commonly bred, a large gene pool is present. for example, in 2004, over 18,000 persian cats were registered. a possibility exists for a complete outcross, if no barriers exist between the individuals to breed. however, it is not always the case, and a form of distant linebreeding occurs. again it is up to the assortative breeder to know what sort of traits, both positive and negative, exist within the diversity of one breeding. this diversity of genetic expression, within even close relatives, increases the variability and diversity of viable stock. laboratory animals systematic inbreeding and maintenance of inbred strains of laboratory mice and rats is of great importance for biomedical research. the inbreeding guarantees a consistent and uniform animal model for experimental purposes and enables genetic studies in congenic and knock-out animals. in order to achieve a mouse strain that is considered inbred, a minimum of 20 sequential generations of sibling matings must occur. with each successive generation of breeding, homozygosity in the entire genome increases, eliminating heterozygous loci. with 20 generations of sibling matings, homozygosity is occurring at roughly 98.7% of all loci in the genome, allowing for these offspring to serve as animal models for genetic studies. the use of inbred strains is also important for genetic studies in animal models, for example to distinguish genetic from environmental effects. the mice that are inbred typically show considerably lower survival rates. humans global prevalence of consanguinity effects inbreeding increases homozygosity, which can increase the chances of the expression of deleterious or beneficial recessive alleles and therefore has the potential to either decrease or increase the fitness of the offspring. with continuous inbreeding, genetic variation is lost and homozygosity is increased, enabling the expression of recessive deleterious alleles in homozygotes. the coefficient of inbreeding, or the degree of inbreeding in an individual, is an estimate of the percent of homozygous alleles in the overall genome. the more biologically related the parents are, the greater the coefficient of inbreeding, since their genomes have many similarities already. this overall homozygosity becomes an issue when there are deleterious recessive alleles in the gene pool of the family. by pairing chromosomes of similar genomes, the chance for these recessive alleles to pair and become homozygous greatly increases, leading to offspring with autosomal recessive disorders. however, these deleterious effects are common for very close relatives but not for those related on the 3rd cousin or greater level, who exhibit increased fitness. inbreeding is especially problematic in small populations where the genetic variation is already limited. by inbreeding, individuals are further decreasing genetic variation by increasing homozygosity in the genomes of their offspring. thus, the likelihood of deleterious recessive alleles to pair is significantly higher in a small inbreeding population than in a larger inbreeding population. the fitness consequences of consanguineous mating have been studied since their scientific recognition by charles darwin in 1839. some of the most harmful effects known from such breeding includes its effects on the mortality rate as well as on the general health of the offspring. since the 1960s, there have been many studies to support such debilitating effects on the human organism. specifically, inbreeding has been found to decrease fertility as a direct result of increasing homozygosity of deleterious recessive alleles. fetuses produced by inbreeding also face a greater risk of spontaneous abortions due to inherent complications in development. among mothers who experience stillbirths and early infant deaths, those that are inbreeding have a significantly higher chance of reaching repeated results with future offspring. additionally, consanguineous parents possess a high risk of premature birth and producing underweight and undersized infants. viable inbred offspring are also likely to be inflicted with physical deformities and genetically inherited diseases. studies have confirmed an increase in several genetic disorders due to inbreeding such as blindness, hearing loss, neonatal diabetes, limb malformations, disorders of sex development, schizophrenia and several others. moreover, there is an increased risk for congenital heart disease depending on the inbreeding coefficient (see coefficient of inbreeding) of the offspring, with significant risk accompanied by an f =.125 or higher. prevalence the general negative outlook and eschewal of inbreeding that is prevalent in the western world today has roots from over 2000 years ago. specifically, written documents such as the bible illustrate that there have been laws and social customs that have called for the abstention from inbreeding. along with cultural taboos, parental education and awareness of inbreeding consequences have played large roles in minimizing inbreeding frequencies in areas like europe. that being so, there are less urbanized and less populated regions across the world that have shown continuity in the practice of inbreeding. the continuity of inbreeding is often either by choice or unavoidably due to the limitations of the geographical area. when by choice, the rate of consanguinity is highly dependent on religion and culture. in the western world some anabaptist groups are highly inbred because they originate from small founder populations and until today marriage outside the groups is not allowed for members. especially the reidenbach old order mennonites and the hutterites stem from very small founder populations. the same is true for some hasidic and haredi jewish groups. of the practicing regions, middle eastern and northern africa territories show the greatest frequencies of consanguinity. among these populations with high levels of inbreeding, researchers have found several disorders prevalent among inbred offspring. in lebanon, saudi arabia, egypt, and in israel, the offspring of consanguineous relationships have an increased risk of congenital malformations, congenital heart defects, congenital hydrocephalus and neural tube defects. furthermore, among inbred children in palestine and lebanon, there is a positive association between consanguinity and reported cleft lip/palate cases. historically, populations of qatar have engaged in consanguineous relationships of all kinds, leading to high risk of inheriting genetic