AP Biology class blog for discussing current research in Biology

Tag: genetic mutations

A Potential Cure: We’ve Waited 151 Years For This!

CRISPR-Cas9 Editing of the Genome (26453307604)


CRISPR, which stands for Clustered Regularly Interspaced Short Palindromic Repeats, is a gene editing tool comprised of DNA sequences from prokaryotes, that is becoming more commonly used to treat and potentially cure life-threatening diseases that have previously been viewed as a death sentence; in December of 2022, a study was conducted at the University of California San Diego School of Medicine, where it was discovered that CRISPR technology can be used to target the gene that causes Huntington’s Disease.


First, we must understand what exactly Huntington’s Disease is. Huntington’s Disease, which was discovered in 1872, is a rare neurological disorder characterized by the gradual destruction of nerve cells in the brain. It is caused by a single defective gene, and this mutation is as dangerous and tragic as it is rare; the disease has no cure, and patients typically do not survive beyond 20 years post-diagnosis. 


However, thanks to CRISPR, it is a very real possibility that that will soon change. 


The study that was conducted at U.C. San Diego involved the experimentation of Cas13d – an RNA editing technique – against toxic RNA and protein buildup that is associated with the HTT gene mutation that causes Huntington’s Disease, and the trial was found to be successful in terms of eliminating that buildup. The experiment was conducted on mice, and it was also discovered that only one injection of the Cas13d therapy was necessary to yield results, and the benefits (improved motor function, lessened symptoms) lasted for eight months.


This discovery is especially fascinating as it connects to our AP Biology units in terms of mutations: The most common genetic mutations are insertions, substitutions, and deletions. The mutation that causes Huntington’s Disease, however, fits into neither one of these categories: if anything, the mutation is considered a duplication, as it is characterized by the unwanted repetition of cytosine, adenine, and guanine; these repetitions are what lead to the protein buildup, and damage the HHT gene. 


In previous years leading up to the U.C. San Diego experiment, trials conducted to target the gene that causes Huntington’s Disease have mostly been unsuccessful, but we can hope that this new discovery is a step in the right direction and may provide the key to figuring out how to treat this disorder that has historically been viewed as a death sentence.

Medicine of the Future

According to researchers at Karolinska Institutet in Sweden, there are many challenges when it comes to using CRISPR gene editing as a part of medicine of the future. One challenge is how cells behave when subjected to DNA damage. 

TopBP1 Activation of ATR in DNA Damage ResponseDamage to cells activates the protein p53. The technique is less effective when p53 is activated, but a lack of p53 allows cells to grow rapidly and become cancerous. The p53 protein gene is a tumor suppressor gene. If a person inherits only one copy of the p53 gene from their parents, they are predisposed to cancer and usually develop numerous tumors, Other linked genes with mutations can have a similar effect to p53 mutations. The transient inhibition of p53 is a strategy for preventing the advancement of mutated cells. The DNA damage response can potentially be a marker in development of more precise guide RNA sequences. 


We have learned thus far in AP Biology that mutations are changes that occur in the DNA sequence of an organism or a change in a genetic sequence. Mutations can be caused by mistakes during cell division. They can be harmful, beneficial or have no effect. 

The researchers plan to further conduct clinic-centered tests in order to understand how pertinent these mechanisms are. This study is largely focused on CRISPR screening experiments on isolated cells and analysis of the DepMap database. 

The Child that Saved Millions

Thousands of years ago a child was born in west Africa with genetic mutation that altered the shape of his/her hemoglobin. This mutation wasn’t harmful because each person has two copies of every gene and the other gene was normal and so they lived and passed on their mutated gene that would save millions of lives.

The gene spread across all of Africa and into parts of southern Europe and India. Every so often two people with the gene would make a child that had two copies of the gene. The child would no longer be able to produce normal hemoglobin. As a result, their red cells became defective and clogged their blood vessels. The condition, now known as sickle cell anemia, leads to extreme pain, difficulty with breathing, kidney failure and even strokes. Most people with this disease die before 40.

In the early 1900s doctors in the U.S first noticed this disease and called its sickle cell anemia because of the way the cells look. Most cases were found in African Americans and studies showed that 8 percent of African Americans had some sickle-shaped blood cells, yet the vast majority had no symptoms at all.

By 1950 doctors had discovered that sickle cell anemia was an incomplete dominance trait and the people who had one copy of the mutated and one of the normal gene showed no symptoms. They soon found out the sickle cell anemia was not unique to the U.S in fact the gene turned up in high rates across Africa, southern Europe and into India. Genetically speaking this made no sense because having two copies of the trait was so deadly it would be most likely that the mutation would have become rarer with each generation.

In 1954 a geneticists Anthony C. Allison observed that people in Uganda who carried a copy of the sickle cell mutation had lower rates of getting malaria. Later research confirmed Dr. Allison’s findings. It seems that the sickle cells defend against malaria by starving the single-celled parasite that causes the disease. The parasite feeds on hemoglobin, and so it’s likely that it can’t grow on the sickle cell version of the molecule.

The Grey Area of Human Gene Editing

The process of Human Gene Editing developed with the goal to prevent future generations from suffering from genetic diseases present in past generations, like our own. Human gene editing, provided it is done only to the correct disease, alters the DNA in embryos, eggs, and sperm to the when reproduction occurs, the gene for the disease or disability is not inherited. However, two weeks ago the National Academies of Sciences and Medicine issued a report stating that human gene editing is being used to enhance people’s health or abilities. This is considered unethical according to organizers of a Global Summit on human gene editing.

Human gene editing has been given a “yellow light” because the process is not yet approved to be done on people. There are high hopes that diseases caused by only 1 genetic mutation such cystic fibrosis and Huntington’s disease will be eliminated due to this process. Unfortunately diseases that are caused by more than one genetic mutation, such as autism or schizophrenia, are not curable by this process.

National Cancer Institute

Gene Editing on humans is such a controversial topic right now: is it ethical to change genes? should the practice be used to change physical appearances? Ultimately, if Human Gene Editing is approves, who decides when it becomes too much, or unethical. This grey area is presented to be somewhere between when it is appropriate to help aid the life of a human, ridding them of a disease, and when enhancements are made.


Why don’t Naked Mole Rats Feel Pain?

This question is currently being researched because of the mole rats amazing inability to feel pain the way that most animals do. The reason lies in sensory nerves. An ion channel is sensitized when molecules bind themselves to receptors which is TRPV1. Scientists performed a test to see what exactly what makes these animals different than others.

They tested the thermal hyperalgesia of both the common rat and the naked mole rat at TRPV1. What do you think the difference is? From this experiment and by looking at the DNA of other animals as well, they concluded that the switch of 1 to 3 amino acids has a great effect on the naked mole rat. This change causes the receptors to be less sensitive to pain. This unique receptor may be the reason that they are able to survive better than other animals with genetic mutations. Also because they do feel as uncomfortable in the heat compared to others, they are able to live in small tightly packed spaces underground.

This topic is very important because it shows how a small genetic difference can be the basis for a species. It is proven that through evolution, they have a slow metabolic rate and that they do not have anything that is not necessary for their survival, including extra pain receptors. More research is being done on this topic to help us better understand why some animals feel pain and some do not.   

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