Inbreeding

From Academic Kids

Inbreeding is breeding between close relatives.

If practised repeatedly, it typically leads to a reduction in genetic diversity. Inbreeding often leads to reduced health and fitness (called consanguinity depression); however, livestock breeders often practice inbreeding, then cull unfit offspring, especially when they are trying to establish a new and desirable trait in their stock.

The most commonly cited problem with inbreeding is that two closely related individuals are likely to have very similar genomes, and if one individual has a gene for a given negative trait, then the other is likely to have it as well. However, Gregor Mendel and his plant breeding experiments show that a single instance of inbreeding is statistically very unlikely to result in a flawed individual, as far as inheriting negative traits goes.

Nevertheless, an inbred individual is likely to possess several physical and health defects, in addition to higher incidence of inheriting a poor trait. They include:

reduced fertility both in litter size and in sperm viability
increased congenital defects
fluctuating facial asymmetry
lower birth rate
higher neo-natal mortality
slower growth rate
smaller adult size, and
loss of immune system function.

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Royalty

The most discussed instances of interbreeding relate to European monarchies. The royal families of Europe have close blood ties which are strengthened by intermarriage. Some examples are:

Queen Elizabeth II of the United Kingdom and her husband Prince Philip are second cousins once removed - both being descended from Christian IX of Denmark, Philip is the great-grandson and Elizabeth is the great-great-granddaughter. They are also third cousins as great-great-grandchildren of Queen Victoria.

Queen Victoria of the United Kingdom married her first cousin, Prince Albert.

The House of Habsburg was famously weakened by intermarriage, leading to a number of birth defects.

Many Egyptian Pharaohs married their sisters.

However, it is not necessarily the case that there is a greater amount of inbreeding within royalty than there is in the population as a whole: it is simply better documented. Among genetic populations that are isolated, opportunities for exogamy are reduced. Isolation may be geographical, leading to inbreeding among peasants in remote mountain valleys. Or isolation may be social, induced by the lack of appropriate partners, such as Protestant princesses for Protestant royal heirs. Since the late middle ages, it is the urban middle class that has had the widest opportunity for outbreeding.

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The Rothschilds

Among the descendants of Mayer Amschel Rothschild, the founder of the famous financial and banking family, many of the men married their brothers's daughters or cousins related through the male line. They also had the tradition that only descendants in the male line could participate in the business, though daughters did inherit considerable wealth. These two traditions were a means of keeping the business closely in the family, for purposes of secrecy. This was the reason that, in 1901, the Frankfurt branch of the family business was closed when the male line that managed it died out.

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Non-human Animals

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

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

The cheetah is a highly inbred species, probably because of a population bottleneck in the species' recent past. Inbreeding is also deliberately induced in laboratory mice in order to guarantee a consistent and uniform animal model. Human genetic diversity is also limited, indicating a population bottleneck some 70,000 years ago.

Purebred animals are often inbred; some critics argue the practice is unhealthy. [1] (http://www.dogbreedinfo.com/inbreeding.htm)

Where a species is threatened by extinction, the population may fall below a minimum whereby the forced interbreeding between the remaining animals will result in extinction.

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