Shubin illustrates this with an example of a couple having a child with a horrific genetic mutation that makes him look sort of like a clown, and he reproduces and his descendants become more and more clownlike. What kind of model could be used to plan this (think Mendelian inheritance!) and why would it be useful? How would genes pass on and mutate like this through multiple generations? How would a scientist be able to look at one of his descendants and determine a relation to him, if they only had their DNA to look at?
Eugene Bulkin (doubleaw002@gmail.com)
Eugene, I’m not quite sure what you mean ‘kind of model could be used to plan this’, but certainly, the way Shubin describes the disease “all of his children are like him: they have a red rubber nose that squeaks and huge floppy feet” (Shubin, 175) it sounds as if it is definitely caused by a dominant gene, like Huntington’s (Campbell, 279). Furthermore, because Shubin only uses male pronouns to describe the family and does not mention affected daughters, I would go on to say that this gene is probably inherited on the X-chromosome and is therefore sex-linked. A pedigree analysis, similar (but larger) to the one Shubin provides on page 176 would help map the progression of these funny traits. I suppose a few rounds of Punnet Squares may also help map the disease and predict the future inheritance of its characteristics, but because there were only three generations of clown mutants, there would not be enough accurate information to plan for the phenotypes of future generations without knowing the genotypes of their parents.
ReplyDeleteGenes would not be able to mutate this rapidly through multiple generations. Usually, only mutations that provide some type of evolutionary advantage survive for more than a few generations. In this case, a red rubber nose would be an evolutionary disadvantage, especially when that clown started looking for a mate, so that in itself would probably prevent the passing on of this mutant gene. Also, it takes centuries for a gene to evolve, not during the course of an average humans life, so genes would not ‘mutate like this through multiple generations’ (Eugene’s question).
Finally, though I find it a bit unlikely that when studying a curious clown mutation a scientists would only be able to study genotype and not phenotype, a scientist would be able to determine the degree of relation in the family members based on genetic mutation. First, the scientist would have to compare the genetic sequences of the members of the family to a person outside the family without the mutation, so comparison would prove who was the grandparents, and therefore also not affected by the mutation. Past that, the scientist could compare which genomes had the most different single nucleotide polymorphisms (SNPs) from the grandparents so as to determine the generation of the individual (Campbell 417). This strategy would only work though if this disease was a genetically inherited one and not some type of problem acquired in development.
(Jackie Edelson, jedelson92@gmail.com)
Shubin models the inheritance pattern and genetic progression of this clown family as a family tree (Shubin 176). Overall, this system of lineage identification is a useful tool in understanding how certain traits became visible in a population. Here we have the instance where two parents give birth to an offspring with a sqeaky nose. Because it the original parents did not have squeaky noses themselves, there are a couple of explanations for this characteristic’s appearance in the offspring. In the context of continuity and change, the genetic code becomes very important. If one considers the patterns associated with Mendelian inheritance, there are a number of explanations. It is possible that both of the parents possess the recessive allele for this trait. This is a phenomenon visible in the diagnosis and progression of genetic disorders within a family. For example, two unaffected people who each carry one copy of the mutated gene for an autosomal recessive disorder (carriers) have a 25 percent chance with each pregnancy of having a child affected by the disorder. The chance with each pregnancy of having an unaffected child who is a carrier of the disorder is 50 percent, and the chance that a child will not have the disorder and will not be a carrier is 25 percent (http://ghr.nlm.nih.gov/handbook/inheritance/riskassessment). It is possible for two individuals without the trait to pass on that trait recessively to their offspring, as can be seen in the clown family. An alternative explanation for the change would be some sort of mutation in the DNA genetic code that affected the synthesis of proteins that in turn affected the development of a certain trait. Duplication, rearrangement, and mutation of DNA contribute to the evolution of the genome (Campbell 438). As time progresses, certain mutations are inevitable. Abnormalities can range from a small mutation in a single gene to the addition or subtraction of an entire chromosome or set of chromosomes. As these mutations occur, it is possible for the phenotype to be altered, which could explain the appearance of “squeaky-nose.”
ReplyDeleteI agree with Jackie’s point that it is unlikely for these drastically varied traits to appear within a few generations, as evolutionary processes take a long time. However, it is plausible that if the genetic code was altered just enough with each new generation that a significant change could be seen. Realistically, the chart on Page 176 is not very plausible as it would take longer for the traits to be established.
The applicability of this system is what is most important. Again, it is especially applicable to the diagnosis and treatment of disease. Although the chances of inheriting a genetic condition appear straightforward, a person’s family history can sometimes modify those chances (http://ghr.nlm.nih.gov/handbook/inheritance/riskassessment). By using a model to examine an individual’s family history, scientists can determine the risk that an individual has for specific genetic disorders like Tay-Sach’s and Huntington’s diseases (Genetic Science Learning Center – University of Utah). It is also possible for scientists to identify possible carriers for the alleles that cause genetic disorders using family history for the genetic disorder to determine allele distribution within the new generations of offspring. In total, modeling family history is an effective and essential tool to understand and predict the trends in genetic disorders, and I personally think that family history models will be utilized most effectively in this field.
Vickram Pradhan 1/2a vickram.pradhan@yahoo.com