Inbreeding
From Freepedia
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.
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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Means to avoid inbreeding
Mammals, most other animals, and higher plants as well, have ways to avoid inbreeding of any sort. They can be mechanical or societal.
An example of mechanical means is the sweet cherry. It has elaborate biochemical mechanism that precludes self-fertilisation and combination of gametes of high genetical similarity. Fruit flies, on the other hand, have a sensing mechanism to do the same thing, and more genetic diversity than expected by random mating is observed even in a closed population.
The incest taboo in humans is an obvious societal means to avoid inbreeding. Mating with close relatives is forbidden, although the meanings of "close relatives" vary. 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.
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 perhaps some 70,000 years ago.
Purebred animals are often inbred; some critics argue the practice is unhealthy. [1]
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.
Inbred humans
Royalty
The royal families of Europe have close blood ties which are strengthened by intermarriage; the most discussed instances of interbreeding relate to European monarchies. Examples abound in every royal families; in particular, the ruling dynasties of Spain and Portugal were very inbred. Even in the British royal family, which is very moderate in comparison, there has scarcely been a monarch in 300 years who has not married a (near or distant) relative. Indeed, Queen Elizabeth II and her husband Prince Philip are second cousins once removed, both being descended from Christian IX of Denmark. They are also third cousins as great-great-grandchildren of Queen Victoria. Other examples include:
- Mary, Queen of Scots and Lord Darnley, parents of James VI & I, were half first cousins, and 3rd cousins once removed
- William III and Mary II, who were joint sovereigns, were also first cousins;
- George I and Sophia of Celle were paternal first cousins;
- George IV and Caroline of Brunswick were first cousins;
- Queen Victoria of the United Kingdom married her first cousin, Prince Albert.
- George V and Queen Mary were second cousins once removed;
- The House of Habsburg intermarried famously ;
- 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.
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.
Westboro Baptist Church
The church group (and alleged cult) Westboro Baptist Church has apparently begun inbreeding, with one of its members, Rachel Phelps, being married to her nephew's brother-in-law, Charles F. Hockenbarger (her newphew, Samuel Phelps-Roper, is married to Charles' sister, Jennifer). Additionaly, though it does not interfere with genetics, Shirley Phelps is married to her step-brother, Brent D. Roper. Long before these marriages took place, residents of Topeka speculated that the church's stringent guidelines against marrying "outsiders," coupled with the lack of potential spouses within the group (nearly 90 of the group's 100 members are related through blood or marriage) would lead to eventual inbreeding. It is unknown whether this pattern will continue or, if it does, how extreme the degrees of inbreeding will become.
See also
- Pedigree collapse
- Compare with: hybrid vigor
- Self-incompatibility in plants (how some plants avoid inbreeding)
- F-statistics
