Inbreeding causes homozygosity, which increases the likelihood of harmful or recessive traits impacting progeny. Inbreeding has the following disadvantages: Continuous inbreeding among cattle causes inbreeding depression. It lowers an animal's fertility and output. This is called "inbreeding depression". Cattle that are inbred too long without replacement will be less productive and more prone to disease.
In humans, inbreeding leads to genetic mutations due to the reduction of diversity within populations. These mutations may be beneficial or detrimental depending on how they occur within genes and cells. For example, a mutation that confers resistance to cancer drugs would be detrimental but a mutation that reduces blood sugar levels could be beneficial during periods of food scarcity. Genetic mutations can also lead to diseases being passed down through families. Examples include cystic fibrosis, Huntington's disease, and Duchenne muscular dystrophy.
In addition to mutations, inbreeding can also increase the risk of acquiring infectious diseases. This is because animals who are closely related have similar immune systems and are therefore more likely to get the same infections. They cannot fight these off easily because they do not have different versions of each gene. This means that they are at greater risk of dying from them.
Inbreeding also has many other effects that depend on the type of inbreeding involved.
Inbreeding causes homozygosity, which increases the likelihood of children inheriting harmful or recessive characteristics. This generally results in a temporary decline in a population's biological fitness (its capacity to live and reproduce), which is called inbreeding depression. Over time, this will also result in a permanent increase in genetic variation within the population, but at a cost to evolutionary potential.
In humans, inbreeding can lead to many health problems, including: dementia, heart disease, diabetes, cancer, low blood pressure, mental illness such as schizophrenia, and even death before age 40. The risk of these effects occurring increases with each additional relative who shares your genes. For example, if both of your parents are siblings, you have a two in one out probability for any offspring they share to be affected by inbreeding (one out of four). If all of your relatives were sibs, then the probability would be 100%. In other words, if you had a choice between having a child with a non-sibling and having a child with a sibling, then choosing a sibling would be worse for your gene pool than choosing someone outside of your family.
In addition to increasing health risks, inbreeding can also have positive effects on traits such as body size.
Outbreeding can cause a decrease in reproductive fitness known as "outbreeding depression," which is less prevalent than inbreeding depression. Inbreeding in small populations often raises the danger of extinction, particularly for species that do not ordinarily inbreed. Outbreeding may also lead to the appearance of new diseases that are not present in inbred individuals. Finally, outbreeding can increase the genetic divergence between populations, reducing their ability to adapt to changing conditions.
Outbreeding can have negative effects on an individual or population for several reasons. First, if the genes responsible for some characteristic or traits are located near the end of a chromosome, recessive alleles may be brought into proximity with each other and might therefore be more likely to appear together in the same individual. Such "gene interactions" could reduce the effect of each gene individually or even eliminate it entirely. For example, two alleles for black hair color might be found together in some people, but because they are on different chromosomes, they don't interact with each other and everyone with these two alleles gets all white hair instead. However, if the two alleles are on the same chromosome, they will be inherited together and so will appear at the same time in future generations.
(ii) Out-crossing, or mating chosen animals with unrelated superior animals of the same breed, helps alleviate inbreeding depression. It aids in the restoration of cow fertility and output. This method is used in commercial dairy herds to maintain or increase genetic gain.
(iii) Zebrocycling is cycling offspring born to female cows through their life. This method is used to maximize genetic gain and reduce the incidence of disease.
(iv) Cloning involves making an exact copy of a cell or tissue sample. This would be done either by extracting the nucleus from a donor cell and inserting it into an egg cell from which the nucleus has been removed or by using nuclear transfer technology where an intact nucleus is inserted into an enucleated ovum. The term cloning also includes the production of cloned animals by combining the nuclei of two cells from different organisms. This can be done by removing nuclei from adult cells (such as skin cells) and inserting them into eggs from which the nucleus has been removed, or by using fetal liver cells or other early embryonic cells. The resulting embryo would then be allowed to develop outside the mother for several days before being transferred into a surrogate mother. At this point, it is called a cloned animal but it would still need to grow up in order to be considered mature.