Biology: The Effects on Inbreeding on Animal and Human Populations
Grace Savedge
Block 3B
Biology Extended Essay
THE EFFECTS OF INBREEDING ON ANIMAL AND HUMAN POPULATIONS
To what extent are biological defects linked to cases of inbreeding and why?
INTRODUCTION
Inbreeding is a controversial topic that has affecting our nations for centuries. Inbreeding occurs when two individuals from the same species mate, which are more closely related than if you had selected them randomly from the whole population. In simple terms it means mating between individuals that are related to one another. Within animals this can mean mating between brothers and sisters, father and daughter or mother and son, although this degree of inbreeding is rarely seen in humans, it can also be observed and is usually seen as mating between cousins and other family members. Inbreeding is a measure of the probability of identity by descent of two alleles at a given locus in a given individual. Locus refers to the location of a gene on the chromosome and an allele is a genetic variant, if there is variation in genetic type at a locus, then you have at least two alleles. Identity by descent is straightforward, it simply means that the two alleles are the same because they derive from the same common ancestor. Loss of heterozygosity (and therefore a gain in homozygosity), whereby loci are more likely to carry identical alleles. As heterozygosity is the biological source of hybrid vigour, this vigour is lost in what is called inbreeding depression; and A decrease in genetic variation for traits. As a practice that has been occurring for many generations the question, what affects does inbreeding have on animal and human populations?, has begun to arise in the scientific community. Through the study of genetics the answer to this question is hoped to be discovered.
This investigation examines the genetic traits associated with inbreeding and the biological defects that can result from it. In order to understand this study there must be an understanding of Genetics. Genetics is the branch in biology which studies the origin, transmission and expression of genetic information, and the variation it causes amongst species. Inbreeding is most commonly used as a technique for the retention of desirable characteristics or the elimination of undesirable ones. This technique has been most commonly used with animals in order to produce offspring with certain desired traits. However, over the years it has been discovered that the descendants of inbreed couples are being born with more genetic defects and are not living as long as their ancestors. In order to discover the cause of these defects, further exploration of genetic genealogy is imperative.
INVESTIGATION
In order to successfully investigate this topic tedious amounts of research on other studies and experiments needed to be done since I personally could not do an experiment. The method chosen was the research three different types of studies revolving around inbreeding within both human and animal populations. The first study chosen is about a certain breed of cow that has a certain genetic disorder linked to it, the second study is based around the effect of inbreeding on humans using a royal family. The family genetic history and family relations is used to prove why incest caused the downfall of the dynasty and how it ultimately led to its extinction. The final study used is also about animals but it focuses on how inbreeding is used to make “pure bred animals” and how the prolonged use of this technique can have detrimental affect on these animals health.
Research Question:
To what extent are biological defects linked to cases of inbreeding and why?
DATA COLLECTION
In recent years many studies have been conducted in efforts to connect certain diseases to inbreeding. In the study Svara et al. Acta Veterinaria Scandinavica conducted in 2016, it was founded that inbreeding is directly related to certain biological defects in Cika cattle. Svara studied two cows from the same farm that both had stillbirths and traced their genetic lineage using a pedigree of their familial relationships that went back five generations.
Familial relationship of the two PHA affected calves. Males are represented by squares, females circles. Full shading designates affected.
Using the pedigree Svara discovered that both the cows previously had multiple normal offspring with different cows but when they were breeded with the same 2-year-old Cika cow their offsprings both had the same genetic defect, since the trait was recessive it meant that both the mothers also were carriers for the disease, meaning that they most likely had common ancestors since it was such a small farm. Based on the information in the pedigree it can be determined that the two affected cows were a result of inbred mother-son and aunt-nephew relations. Furthermore the two dams were found to be paternal half-sisters and had the same maternal grandmother. As a result of the mothers having the same lineage both of their offspring had the same genetic deficiencies, gross lesions were similar in both affected calves. Their bodies were severely deformed due to severe diffuse subcutaneous oedema with multiple cysts of various sizes, filled with serohemorrhagic fluid. This is recessive gene for Cika cows so when Svara discovered that two cows from the same farm had the same disease she used a pedigree to put inbreeding at default.
As well as in animals, inbreeding can also have an affect on the genetic makeup of humans. A great example of this is the extinction of a European royal family. In 2009 Gonzalo Alvarez did a study, from the genetic point of view, as to whether or not inbreeding was the major cause responsible for the extinction of the Spanish Habsburg dynasty. Alvarez used an extended pedigree up to 16 generations in depth, involving more than 3,000 individuals. He found that the inbreeding coefficient of the Spanish Habsburg kings increased strongly along generations from 0.025 for king Philip I, the founder of the dynasty, to 0.254 for Charles II and several members of the dynasty had inbreeding coefficients higher than 0.20. The inbreeding coefficient uses an equation to measure the degree of consanguinity between two individuals, it is the probability that an individual receives at a given locus two genes identical by descent due to the common ancestry between his parents.The last king of the Spanish Habsburg dynasty was Charles II and as stated earlier he had the highest inbreeding coefficient in his family. Charles II presented important physical and mental disabilities, he suffered from a number of different diseases during his lifetime, the main ones being pituitary hormone deficiency and distal renal tubular acidosis. Alvarez speculated that the health problems suffered by Charles II could have been caused by the action of detrimental recessive genes given his high inbreeding coefficient with 25.4% of his autosomal genome expected to be homozygous. Since Charles II suffered from two rare genetic disorders that are both determined by recessive alleles but carried at two unlinked loci it is assumed that his disorders are a result of inbreeding. Alvarez came to the conclusion that the probability of an individual suffering from two very rare recessive traits is low but inbreeding can increases those chances and cause an association of two recessive traits even for unlinked loci.
Another main issue related to inbreeding is its manipulated use within animals in order to create purebreds. Although pure bred dogs are coveted for their beauty and desired for certain traits they often suffer for many problems caused by inbreeding. The main issues with continuously making purebred offspring is that in order to make a purebred you need to animals from the exact same gene pool. As a result this severely limits the gene pool variety and then on top of that most breeders will animals from the same family causing and even higher inbreeding coefficient. Most frequently this method of breeding is used within dogs and recent studies have put it at blame for many disease found in dogs like, higher risks of cancer and tumors; eye and heart disease; joint and bone disorders; skin, immune system and neurological diseases; and even epilepsy. “One study found that ten thousand pugs have the same genetic diversity as 50 individuals”(barnes). This means that most inbred animals will be more likely to receive the negative recessive genes from their lineage causing them to have severe health problems.
WORK CITED
Carol Beuchat. “COI FAQS: Understanding the Coefficient of Inbreeding.” The Institute of Canine Biology, 6 Apr. 2015, www.instituteofcaninebiology.org/blog/coi-faqs-understanding-the-coefficient-of-inbreeding.
The Editors of Encyclopædia Britannica. “Inbreeding.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 28 Apr. 2017, www.britannica.com/science/inbreeding.
Razib Khan. “What Is Inbreeding?” Gene Expression, 22 July 2012, blogs.discovermagazine.com/gnxp/2012/07/what-is-inbreeding/#.WgG1UkyZN-U.
