Why does inbreeding cause genetic defects

This increases the risk they will both pass a copy of the gene onto their offspring. We have several tools available to prevent matings between animals that carry the same recessive gene. Our DataMATE app makes it easy for our artificial breeding technicians to calculate the risk of a particular mating. DataMATE issues a warning if the animals are likely to share more than 6. The technician can then inseminate the cow with a more suitable bull.

DataMATE also helps prevent matings between bulls and cows carrying the same recessive gene. We use your herd records to prepare a DIY Mating Report advising you which cow-bull matings to avoid. Whole herd DNA parentage testing can also help reduce the risk of inbreeding by correctly matching calves to their sires and dam. This can lead to accidental inbreeding once those calves are mated. However, it is very rare to have both. Mice used in lab experiments are often inbred, as the similar genetic structures enable experiments to be repeated.

Controlling outcomes is also the motivation for inbreeding in the farming industry, with cows being bred to increase milk yields and sheep are careful selected to produce more wool. There is evidence that suggests inbreeding certain animals can have more of a negative impact than a positive one. The two largest populations of koalas in Australia could cease to exist by just one disease, due to them being so so heavily inbred, scientists have warned.

A study, headed by Dr David Balding , examined inbreeding in pedigree dogs. Like the animals bred for farming, particular traits are encouraged in pedigree dogs, including their height and the quality of their fur. The study found that a large proportion of pedigree dogs suffered from conditions caused by recessive alleles such as heart disease, deafness and abnormal development of their hip joints.

The problem is more alarming than it might seem on the surface. The reproductive patterns of Pyemotes boylei, a type of mite, are built around inbreeding. The mother mite keeps her eggs inside her until they reach maturity and the first wave to hatch is male. Sometimes, that's created some pretty dramatic results - consider the Doma people of Zimbabwe, whose long isolation and extensive inbreeding has actually resulted in the widespread prevalence of ectrodactyly, in which their middle three toes are completely absent and the outer ones are turned inward.

In point of fact, we're all technically inbred, if you go back far enough, because simple math demands that we have to be. Our number of ancestors grows exponentially with each generation, from two parents to four grandparents to eight great-grandparents, and so on. In less than a thousand years, you've accumulated tens of billions of ancestors, more than the amount of humans who have ever lived on this planet. This means you have to have a bunch of overlapping ancestors, even if they're all buried so far back in your family tree than none of your later ancestors were aware they were marrying their distant cousins.

This necessary duplication of ancestors is known as pedigree collapse, and Cecil Adams provides this example of how extensive it is :. Demographer Kenneth Wachtel estimates that the typical English child born in would have had around 60, theoretical ancestors at the time of the discovery of America.

Of this number, 95 percent would have been different individuals and 5 percent duplicates. Sounds like Invasion of the Body Snatchers, but you know what I mean. Twenty generations back the kid would have , ancestors, one-third of which would be duplicates. At the time of the Black Death, he'd have had 3.

The maximum number of "real" ancestors occurs around AD - 2 million, some 80 percent of the population of England. Admittedly, this sort of inbreeding is really more philosophical than genetic. Again, this is a matter of exponents.

Of our 23, protein-coding gene base pairs, we get 11, from each of our parents, 5, from our grandparents, 2, from our great-grandparents, and so on. That repeated division means that by the fifteenth generation - which is only a few centuries ago - your average ancestor assuming zero inbreeding is contributing, on average, less than a single gene to your current genome. Go back a thousand years to the 30th generation, and the average genetic contribution is effectively zero.

While it isn't really accurate to say that we're all inbred, at least not in a genetic sense, it might actually be fair to say that we're all the descendants of inbred people. Numerous theories have been put forward about a huge decrease in the human population tens of thousands of years ago - one particularly extreme version suggests the human population in sub-Saharan Africa remained under 2, for as much as , years, while more moderate hypotheses suggest a population bottleneck of about 15, that occurred about 70, years ago.

Either population bottleneck would most likely necessitate fairly extensive inbreeding, and that's backed up today by the relatively low level of genetic variation within humans. So, what can we say about inbreeding, in the end? There's no way of escaping the fact that it does increase the risk of birth defects, particularly over multiple generations, and it can have some fairly horrific consequences.

That said, the risks of limited inbreeding do seem to be pretty massively overstated, and inbreeding by slightly more distant relatives like third cousins might actually confer a significant benefit. And, depending on just how low our population got in our deep prehistory, it's entirely possible that without inbreeding, the human race would have long since gone extinct.

Consanguinity, human evolution, and complex diseases by A. Bittles and M. The genetics of inbreeding depression by Deborah Charlesworth and John H. Ceballos, and Celsa Quinteiro. Berra, Gonzalo Alvarez, and Francisco C. Recessive Genes Diagram via Wikimedia Commons.

Albert and Elsa Einstein via Wikimedia. Didn't it turn out in the end that George-Michael and Maeby weren't biological cousins, since Lindsay was adopted by the Bluths? The team was also just looking for the most extreme examples of inbreeding. Ultimately, this is another step for research efforts into the prevalence and lasting effects of inbreeding.

New genetic resources are making this kind of research easier and more accessible — before the advent of genome sequencing and genetic databases, this study would have been impossible.

Register or Log In. The Magazine Shop. Login Register Stay Curious Subscribe. Charles II, the last of the Spanish Hapsburgs. Generations of inbreeding left him infertile, in addition to numerous additional health problems. Credit: Wikimedia Commons.