Presentation on theme: "ZOL 341 FUNDAMENTAL GENETICS HONORS OPTION VAMPIRISM Curtis Matzke."— Presentation transcript:
ZOL 341 FUNDAMENTAL GENETICS HONORS OPTION VAMPIRISM Curtis Matzke
Introduction Tales of vampires, werewolves and other such blood-craving mythological creatures have been told for hundreds of years. The influence of such tales have branched into all forms of media, most notably those of literature and film, in which a creature, the vampire, transforms or “infects” a human being through drinking their blood, thus turning them into some ungodly creature not unlike themselves. The following presentation attempts to examine such a case as if it actually occurred. With the use of genetic study we will attempt to scientifically and medically explain this “disease,” often referencing a fictitious character, Tim, who became infected after spending time in a mysterious town who had an unusual habit of drinking blood, as well as data gathered from this town. We begin by examining three different modes of inheritance tracing the increased craving for blood.
Autosomal Dominant Inheritance Key: AA, Aa, A_ = affected aa = unaffected Variance due to gene being on autosomal chromosome.
Autosomal Recessive Inheritance Key: aa = affected AA, Aa, A_ = unaffected Variance due to gene being on autosomal chromosome.
X-Linked Inheritance (Dominant) Key: X + X, X + X= affected XX, XY = unaffected Variance due to gene being on X chromosome.
Variance ENVIRONMENTAL Definition: Component of the phenotypic variance that is due to environmental differences among individual members of a population. This would lead us to believe that the cause of such cravings is due to outside factors that could include pollution, infections, or the fact that so much blood is being drunk by the host a “thirst” is merely acquired. GENETIC Definition: Component of the phenotypic variance that is due to genetic differences among individual members of a population. This would lead us to conclude that those with greater cravings possess a genotype that codes for such increased cravings, while those with less or no such cravings lack this gene(s). Transmitted within families autosomally or on the X chromosome as seen in the pedigrees. Also, genic interaction variance (interactions between genes at different loci) may contribute. The entire community drinks blood, therefore the variation is with cravings and quantity consumed. Two types: Likely a combination of both. Also, Incomplete Dominance may be occurring as in Sickle Cell Anemia, in which an intermediate between the two homozygous phenotypes exists.
Gene Mapping To map the gene/genes involved in this disorder, using the pedigrees and location of known genes, one would calculate the lod score to determine the probability that the genes are linked and estimate the recombination frequency. First determine the genotypes of the individuals in the pedigree for the genes of interest considering recombination and where crossing over may have taken place. Continue by calculating the probability of obtaining the observations with (a) the assumption of linkage with a specified degree of recombination and (b) the assumption of independent assortment. Determine the ratio of these probabilities and the logarithm of which is then the lod score. Lod score < -2 significant against linkage (independent assortment) Lod score 2 < lod < 3, uninformative Acceptable lod score: Lod score > 3 (convincing evidence for linkage) Looking at linkage and independent assortment
Molecular Identification In order to molecularly identify the gene involved in this vampire disorder, measure the genetic variation by using various molecular markers. Use Electrophoresis in order to separate the electrical charges of protein, DNA, and RNA. Includes: –Protein Electrophoresis –Restriction fragment length polymorphism (RFLP) –VNTR/STRs –Sequencing RFLP would be best to cut the DNA molecule (with the same restriction enzyme) and produce a variation in the pattern of fragments and identify the DNA sequence and map the gene. Patterns appear on an autoradiograph gel: For further analysis, one could use Nucleic Acid Hybridization to identify specific DNA sequences/ fragments. FISH could be used to identify specific parts of the chromosome (not molecular). See Detection slide.
Infection It is know that Tim, the male individual who began displaying symptoms, is described as having spent time in an isolated community that drinks blood. He stayed with these people, sharing meals and drinking from communal dishes. After leaving, he was fine for several years until he and his sexual partner become symptomatic, and with greater severity. Because of the infection of Tim’s sexual partner, it is reasonable to conclude that the infection was not directly from pollution or food in the community. I would speculate that the infection was likely due to fluid transfer between people, such as a sexually transmitted disease Common in vampire folklore, one is transformed into a vampire by biting ones neck, which would be considered as fluid transfer. It is possible something such as this occurred to Tim in the mysterious community and then passed it on himself to his sexual partner through sexual intercourse (it’s also possible Tim became frisky in the strange community and was thus infected with an STD from the start).
Autoimmune Theory An additional theory is that this could be some sort of autoimmune disease, or, rather, there is an autoimmune factor that is contributing to the disease. Although autoimmune diseases are typically do not spread from person to person as with Tim, it may explain the presence in the mysterious community. Some autoimmune diseases, in fact, are known to begin or worsen with certain triggers such as viral infections. Genes also contribute to susceptibility for developing an autoimmune disease. Such facts may explain the variance in severity seen among those in the community.
Retroviral Theory It is yet another possibility that this infection is transmitted through a retrovirus. Retroviruses sometimes possess long incubation period which are common of lentiviruses. This is what was seen in Tim, who became symptomatic after several years. It is therefore feasible that the virus contains code for a protein that interferes with the pathway for the production of heme (predominately carries oxygen in the blood), through some mechanism such as feedback. The virus may be inserting itself several times, producing more product and thus more variation occurs. This theory, as well as the autoimmune theory, is simply additional information/ ideas that merely attempts to explain a fictitious disease and need not be taken as unflawed.
Gene Movement Clearly, this disease is communicable as it was passed on to Tim and from Tim to his sexual partner. The mode of inheritance for the gene(s) responsible is shown in the pedigrees earlier. This situation can be described as participating in gene flow in which there is a transfer of alleles of genes from one population to another (in this case into the United States through Tim). Local inbreeding in the small town where Tim became infected could have previously reduced this gene flow. This new migration may thus prevent genetic divergence between populations and increase genetic variation within populations. It is also possible that susceptibility genes contribute to individual risk of developing the disease as different alleles may be associated with different degrees of susceptibility, or risk. The gene has moved from Europe to the United States as the alleles involved in the disease susceptibility, phenotypic expression, etc. were transferred through Tim.
Detection There are various techniques that could be used to detect the vampire infectious agent. Begin, of course (as is the case with vampires), by obtaining a blood sample. Here are some possibilities: –Run a microbe culture of a diseased sample to see if the cause is bacterial. Observe with microscopy. –Run various biochemical tests. –Run scans (X-rays, CAT scans) of the infected person to detect any abnormal growths. –Run a karyotype such as SKY to see if any chromosome abnormalities exist. –Use PCR to quickly amplify the DNA, making detection and diagnosis simple. –Use Fluorescent In situ hybridization (FISH) to to identify specific parts of the chromosome (the gene, genetic transfer, etc...)
(I’d probably call Dr. House first) The symptoms indicated include severe anemia, altered craniofacial structures, and severe mental afflictions displaying behavioral patterns normally associated with a feral animal. In order to cure the patient, I would begin by treating these symptoms. Treat the anemia through vitamin B-12 injections, prescribing iron supplements, or performing a blood transfusion. Based on the severity of the anemia, a blood transfusion would likely be the most effective initially. To treat any craniofacial alterations, I would begin by ordering a head CT to determine the presence of any tumors or abnormalities. Surgery may likely be the only curative treatment. Treatment
If patient exhibits Porphyria (which may include symptoms of photosensitivity and delusions, which are common in Vampires) treat with heme and carbohydrates. Gene therapy is another alternative to treat the heritability factor of the disease (or theories mentioned earlier) and alter the genetic makeup of the patient’s cells through recombinant DNA. If lycanthropy or other mental symptoms remain, I would consult a psychologist, continue to run scans, and prescribe medication as needed. In all cases I would advise that the patient remain under observation for several weeks and recommend that their doctor begin to publish his findings as Vampires don’t come along very often.
Distribution If this is a rare allele of gene, we asses it’s distribution in the population of individuals by using Hardy-Weinberg Law. This law states that, under certain circumstances, allelic frequencies will not change and genotypic frequencies stabilize after one generation in the proportions p 2 (frequency AA), 2pq (frequency of Aa), and q 2 (frequency aa), where p equals the frequency of allele A and q equals the frequency of allele a. An example of this situation is demonstrated on the following slide. It is also important to mention the possibility of mating between relatives and if certain alleles are identical by descent. Inbreeding increases the chance of having progeny that are homozygous for a rare recessive trait or allele. But Inbreeding by itself does not change allele frequencies. This vampire situation is ideal in examining inbreeding because the number of offspring is limited and isolated (a small community) and the genetic disease phenotype is rare, recessive, which means the Hardy-Weinberg principle can be applied. Also note that rare alleles can be lost in genetic drift.
Distribution Example Remember: the Hardy-Weinberg principle states that q2 + 2pq +p2 = 1 and that q + p = 1. Let us suppose that an autosomal recessive gene codes for our disease. This means that q 2 = aa = diseased phenotype, 2pq = Aa = carrier, and p 2 = AA = normal phenotype. Suppose we look at a population of 100 people, 36 of which are diseased (= aa), therefore q 2 = 36/100 = This is the phenotypic frequency. From here, find the allelic frequency (q) by taking the square root of.36 0.6. Using p + q = 1, the allelic frequency of p = 0.4, which can be used to find p 2. Find the frequencies of the heterozygotes and the homozygote dominants: (p 2 = frequency AA = 0.16), 2pq = frequency of Aa = 0.48). Now multiply the population size (100) times the p 2 (= 16) or 2pq (= 48) value obtained to determine the actual number of people that have those respective phenotypes (recessive phenotype already given = 36). To assess the distribution, add up the number of Aa and aa phenotypes (= 84) to say that this many people have the allele that codes for the disease, but only the aa phenotypes (36 people) are diseased (aa).
Polygenic Trait If this is a polygenic characteristic (multiple loci/genes), we are able to determine the number of genes affecting the trait fairly easily (with humans we must use what information we have since we can not actually “cross” people). Polygenic inheritance increases the number of loci and phenotypes. First look at two individuals heterozygous at a single locus (Aa and Aa = F1) who each had parents homozygous for different alleles at a single locus (AA and aa for both = P). ¼ of the F2 offspring should theoretically be like their grandparents (P). If the P generation was homozygous for different alleles at TWO loci, then ¼ * ¼ = 1/16 of the F2 would resemble the grandparents. So, (¼) n = those similar to the parental (P) generation. Use this equation when looking at progeny numbers and work backwards (ex: see that 1/256 = (¼) 4 4 genes at separate loci with segregating pairs of alleles). Note: this method requires using homozygous strains, assumption that the genes have equal, additive effect, and the loci are unlinked, thus providing limited application. One gene, two gene, hahaha!
Symptom Severity There are many reasons as to why there was an increased severity in the symptoms (mental afflictions, severe anemia) of Tim’s sexual partner. One such reason could be that she simply has or lacks a gene or genes that influences the expression and severity the disease (mentioned earlier). “Just because you have it, doesn’t mean you’ll get it!” Anticipation (also a potential factor in variation of cravings mentioned earlier) There could be an increase in disease severity through generations, though in the case with Tim’s sexual partner it is passed rather than inherited. An example of such hereditary diseases include Huntington’s or Fragile X-syndrome. A threshold trait — Could be present or absent — Expression depends on the risk of having it. — Tim’s sexual partner may have a lower threshold that caused more severe symptoms sooner, while Tim did not become symptomatic after several years because he has a higher threshold.
THE END ? Various References Used: Dr. DeOcampo’s ZOL 341 powerpoint slides Genetics A Conceptual Approach Second Edition by Benjamin A. Pierce Etc…