Genes and Mental Illnesses: Is There a Connection?

Drain C.

Genetics, Stockton University

https://www.sydney.edu.au/news-opinion/news/2024/04/29/do-our-genes-play-a-role-in-depression--.html

Psychologists have been studying the brain and the cause of mental illnesses for at least 150 years. Many have claimed that the outside environment along with trauma have been the main cause of a mental illness. It was a relatively recent connection to study it with genetics/the gene. There are some who have worked with geneticists to point out, that there may be more than one connection between the brain, the mental illness and the gene. Genes tend to copy specific information from parents and pass it to their children. Coding a string of proteins that call for the makeup of a mental illness may not be any different than them coding it for hair color. There have been studies that show the coding sequences for certain mental illnesses such as depression may have overlapping codes for ADHD and schizophrenia as well. So removing a person from a harmful environment may not be the end all factor, if a certain mental illness was already programmed into a hard drive. 

This specific study is showcasing the reactive depression vs the endogenous depression. Meaning- are there people who have it developed due to environment or are people just born with it. Will those born with it built in have less of a stressful environment or more of a stressful environment, may have been one of the main questions that the study was trying to find out. A study across 14,000 people have showed that those with the genetic makeup of a mental illness has reported MORE of a chance of stressful factors. 

However, it is more complex than that because the study later showed that there was a combination of all factors involved (biological, environmental, and genetic) and that they were not independent of another. Other studies have not only tested genes vs depression but have extended the study to depression, genes and twins. Will those who share similar DNA be more prone to the same mental illnesses? The study tested fraternal twins vs identical twins to see if there was more or less of a link together. A main showcase of the study was pointing out that although the twins shared a lot of similar DNA how they processed the outside environment was different, thus furthering the endogenous vs reactive argument. 

https://www.sciencedirect.com/science/article/pii/S0022395624004278

edit: due to a miscommunication in registering I just copied and pasted my own work from a different account. Not plagiarizing or stealing someone else's work.  

 

Do Identical Twins Have Identical DNA?

 

Although identical twins may look pretty similar, at the DNA level, they are not. Identical twins tend to differ by 5.2 genetic changes researchers have suggested in an article. Monozygotic twins, also referred to as identical twins, come from a single fertilized egg and are often studied to determine if particular traits, diseases, or even conditions can result from genetics or environmental influences. For many decades people often thought that identical twins were genetically the same because they are so similar; therefore, differences in their health were considered to be the result of their surrounding environment. But new research has suggested otherwise and that these genetic changes could also account for differences between twins. Researchers in Iceland have interpreted the complete genetic makeup of 381 pairs of identical twins. For 38 pairs, they were genetic duplicates of each other, but differences in DNA were shown that most likely arose in early development. For 39 pairs, there were many differences between twins' DNA, with some having more than 100 changes between them. The patterns of mutations seen by researchers within the genetic DNA of twins suggest that the embryos do not split neatly when twins form. Some twins may arise when a single cell or even a small group of cells split off from the embryo. The number of cells a twin originates from determines how genetically different they are from their twin. If there are more uneven splits of the embryo, that tends to lead to increased differences between twins.

To me, this article was fascinating to learn about and to know that at such an early stage in life a little change in genetic mutations can differ a whole sequence of someone's genetic makeup. I have always thought that identical twins were identical in their genetic make, therefore that is why they look so similar. It's amazing to be see what we can learn by genetic research. 

All identical twins may share a common set of chemical markers on their DNA

Identical twins share many things, including DNA but new research suggest there is a signature of the twinhood. Part of the  epigenome, which are chemical markers that influence genes without altering sequence. These signatures could be used to identify a twin who might have lost their sibling in the womb or separated at birth. It is known that monozygotic twins form from the same zygote splitting into two embryos during development, but it is not clear why it happens is unclear. Scientists begin to look at the epigenetic differences along 450,000 sites of the genome of roughly around 6,000 monozygotic twins and dizygotic. 834 sites in identical twins were highly similar, from young to old twins, and from geographically different locations. These markers were very common among the twins that as of now, there is an 80% accuracy of identifying a twin who might have lost their sibling without even knowing that were a twin.

Twins sharing a Chemical Marker on their DNA

Twins not only share similar sequences of genomes but share the same chemical properties that influence gene expression. These markers are called epigenetic tags and they are used to identify identical siblings that were separated from birth. Van Dongen and her colleagues observed epigenetic differences along 450,000 sites of the genome. They compared fraternal twins to identical twins to get more of a precise understanding of how identical twins may have more similarities than just genomes, and it would rule out any epigenetic changes that will originate from any unusual experience. For identical twins, they saw that 834 spots were similar in chemical markers. These markers included similar centromere and telomere regions. Other marks were identified were near genes that regulate early development. Because researchers don't know what causes a cleavage to form during the formation of identical twins, they believe chemical markers can be utilized to study the aftermath of the cleavage formation and to get a better understanding of how cleavage occurs. 

The Genetic Roots of Sleep Issues and Autism May Be Related

According to a new study of autistic people and their relatives, the genetic factors that have a role in autism may be entwined with those that underlie insomnia. This discovery may be able to help explain the common co-occurrence of autism and sleep issues. According to previous research, up to 90 percent of people with autism encounter disrupted sleep, and approximately 30 percent have a clinical diagnosis of a certain sleep disorder. The study reveals that close relatives of those with autism are also at a high risk to develop insomnia.

50,097 autistic people, along with nearly 56,000 of their full siblings, 31,669 half-siblings and 214,665 cousins were identified by using the Swedish national health registries. Approximately 23 percent of the autistic participants suffered from insomnia or took melatonin, in comparison with 1.1 percent of the control group participants. The study showed that the more closely related the relatives are to the austistic individual, the higher the chances that they will suffer from sleeping issues. For example, identical twins had about 6.6 times the typical odds of suffering from insomnia, while cousins had approximately 1.3 times the usual odds. Out of this study, shared genetic factors explained 94 percent of the correlation, whilst nonshared environmental influences accounted for only 6 percent.

Helpful Links:

Study: Etiological links between autism and difficulties in initiating and maintaining sleep: a familial co-aggregation and twin study

Article: Genetic roots of sleep issues, autism may be entwined

Armadillo Quadruplets shed insight on human identical twin DNA expression

 

    The nine banded armadillo is wholly unique when it comes to its offspring. Without fail, a female armadillo will give birth to quadruplets, all genetically identical. This is due to the fertilized egg splitting twice, creating four embryos before they are implanted in the uterine wall. Also that nine banded armadillos can have distinctly differing personalities and behaviors after birth is also intriguing for the scientists, but still have the same genes. There could be also slight physiological differences between offspring. Since armadillos have the 32 pairs of chromosomes to play with , it could lead to greater variety of the genome. Also that early in development, the X chromosome of the embryos will start suppressing parts of the genome at random. Silencing some genes while activating other genes that make slight differences in the offspring's DNA. Also they factor in the environmental changes that could affect behavior, the majority of how the personality is determined is still a black box . What ever genes that affect personality go in, the expressed personality and behaviors come out.

A Louisiana research facility studies the nine banded armadillo for Hanson's disease (leprosy) and its transmission to humans, possible inheritance, testing methods to detect leprosy ,sequencing the genome and strains of leprosy and medicines to treat the disease. Scientists could have new model to study gene expression and heritability. 

It could shed insight on how human identical twins could have differing genes from the same sequence and how it affects their health. 

The Unethicality of Human Cloning

    A multitude of possible technological and biological advancements arise from human cloning: ridding infertility, understanding and combatting disease, eliminating liver and kidney failure, reversing the aging process, saving endangered/extinct species, etc. The reproductive cloning of humans will grant researchers a better understanding of the human genome, therefore allowing them to successfully pursue the aforementioned possibilities. Even with the numerous beneficial aspects, human cloning (on an individual scale, not with tissues) has been called for a United Nations ban by more than 60 of the world's leading science academies. Why would these science academies push for the ban of human cloning knowing the endless opportunities it may provide?

    Psychological, social, and physiological risks associated with the reproductive cloning of humans are condemned universally. These risks introduce an increased likelihood of the the loss of life. The cloned embryo requires thorough investigation to prove its fitness and viability; even after implanting the successful cloned embryo into the womb, the pregnancy itself may fail. The loss of one life is constitutes as too much. In 2007, an experiment suffered through 100 failed attempts before successfully cloning a macaque.

    Additionally, human reproductive cloning endangers individuality. Human identity would be compromised and diversification would decrease. Monozygotic twins, colloquially known as identical twins or natural clones, often report lacking a sense of individuality. The birth rate of identical twins is 0.4% (1 in 250, or 4 in 1000). Logically, the increase in "clones" ensues an increase in those reports.




https://science.sciencemag.org/content/277/5323/195.full

https://www.britannica.com/science/cloning/Ethical-controversy

Does you genes affect your workouts?

 

Exercising can be different for everyone; some people can have results sooner then others and some have more motivation than others. This NY Times article explains this. It talks about a study that was published in the Journal of Physiology. In this study, they got 42 pairs of twins (30 identical, 12 fraternal) to workout together for two three-month periods. In this first period they ran or cycled for an hour three times a week, then in the other period they lifted weights for an hour three times a week. In the study, almost all of the people that lacked in one period, succeeded in the other.  In the article, it states there was little evidence that genes shaped the outcomes because the twin’s responses are all different. Although this study was useful, I believe a lot was left out to consider like: did all the twins try hard every workout, were they eating right, did they all start at the same level? All of these questions could affect the results greatly. Overall, I still believe genetics affects working out which disagrees with this article. Many factors were not mentioned which makes me think the reason why the twins were receiving the same results is because of all these differences. I believe exercise is affected by both your genes as well as your environment. This would make some of the twins have similar results or different results depending on many different factors including genes. Genes may make someone better at one task, but if a person is more passionate about another they may try harder resulting in more progress in that one.

Extra resource

Study Shows Genetic Makeup Influences Dog Ownership

Did you know you could inherit a genetic component that effects the likeliness of dog ownership? A study was recently posted to Scientific Reports by a few researchers at Uppsala University in Sweden. For the study, they compared the genetics of 85,542 individuals. Out of these individuals, 50,507 had a twin, where 35,035 pairs included both twins and 15,472 only included one of the twins. Both identical (monozygotic) and nonidentical (dizygotic) twins were present in the study. The purpose of comparing both types of twins was to identify what gene structure is actually different. In this case, if any genes specifically matched among dog owners. The objective of the study is to determine if dog ownership is something heritable.

Structural equation modeling was used to examine the study population. The three main groups were classified as:
A- the contribution of additive genetic effects
C- common/ shared environmental effects
E- unique/ non-shared environmental effects

As you can see from the graph, it is noted that shared environment factors (C) only seemed prevalent in young adults.

In conclusion, evidence of distinct genetics plays a role in dog ownership with adults. Out of the study participants, about 10% were identified as dog owners. Further, dog ownership varied by sex and age. Dog ownership was present in 66% being females and 34% being males (see Table 1).

OC with Yogi

This article was interesting to me because I have lived with a dog since I was two years old. Also, I hope to be a veterinarian one day. So maybe this has something to do with my genes! I believe dogs are a huge factor in the progression of human civilization. Aside from dogs being domesticated thousands of years ago to aid human beings, look at how our relationship with these animals effect society today. Most people approve of animal shelters, veterinary care and pet stores. For what? Dogs (and cats)! It is amazing how dogs have transitioned from being property to being loved as a family member.

Can't Sleep? Blame Your Genes

A recent article published in "Medical News Today" claims that insomnia may run in the family. According to the article, a person's genetics have a strong influence over whether or not they will suffer from insomnia. A 2015 study conducted on both identical and nonidentical twins at VCU discovered that, usually, if one twin has insomnia, the other twin is more likely to suffer from insomnia as well. Because identical twins share the same DNA, this suggests that there likely is one or more genes that cause or can be linked to insomnia. With this information, the next step has become identifying what specific genes have a correlation with insomnia. Multiple studies have been able to isolate a few of the genes that lead to insomnia. The data also suggests that there are genes that are exclusive to men and women that can affect one's sleep habits. One large study of the genome of over one million insomniacs has found about 956 genes across 202 locations on various chromosomes that possess some kind of link to insomnia, while a second, smaller study found 57 locations. Most of these genes affect the development of various parts of the brain associated with processing external stimuli. This may be contributing to the restlessness associated to the inability to fall asleep. However, this article also clarifies that genetics alone does not lead to insomnia, as stress levels and different lifestyles can contribute toward insomnia as well.

I found the relationship between genetics and insomnia somewhat surprising. In the past, I thought of insomnia as a symptom rather than a disorder. I thought that if you had one night where you could not fall asleep, than that night you suffered from insomnia. I did not view insomnia as a persistent disorder or disease, which it technically is. While insomnia can be broken down into acute or chronic, I believe the fact that it can be genetic makes me view insomnia more as a disease. Despite the fact that treatments such as sleeping pills already exist, I believe that this increased knowledge about insomnia and how it can be caused will lead to better, healthier solutions to the long, sleepless nights that many humans find themselves afflicted with.

Semi-Identical Twins

An article in the NY Times discusses the discovery and occurrence of neither fraternal nor identical twins, but semi-identical twins; also referred to ask sesquizcgotic twins. The twins share 100% of their maternal DNA and overlap on portions of their paternal DNA. Therefore, the twins are approximately three-fourths identical. 

At 14 weeks, Dr. Nicholas Fisk, a maternal fetal medicine specialist at the Royal Brisbane and Women’s Hospital, inspected an ultrasound and observed one body and one girl, sharing a placenta. Normally, identical twins develop when a single egg is fertilized by a single sperm and splits into two. However, regarding the semi-identical twins, Dr. Fisk suspects that a single egg was fertilized by two sperm before dividing because when the initial sperm entered the egg, the membrane failed to lock down to stop any other sperm from entering. Although, even if another sperm got into an egg, typically, it would result in three sets of chromosomes and a fatal outcome but this time it did not. 

Therefore, Dr. Fisk and his colleagues conducted an analysis of every single chromosome in the boy and the girl. They found no negative abnormalities, the mother had two healthy babies. Each baby contained the normal number of chromosomes, however, there were some areas where their DNA was identical and others where it was different, hence the term "semi-identical" twins. The children were monitored through out their childhood. By age 4, they were meeting all of their developmental markers by the appropriate time. Dr. Fisk sought to determine whether this phenomenon was more common than previously thought. He reviewed genetic data from nearly 1,000 fraternal twins but did not find any semi-identical twins among them. 

The discovery of the concept of semi-identical twins bring about a new phenomenon regarding the way in which mammalian eggs can be fertilized. More research needs to be conducted in order to find out the exact process by which this occurrence is possible.  

Determining which Twin Committed the Crime

An article in the NY Times, discusses a method in which to distinguish between identical twins by their DNA. Since it is estimated that roughly 1% of all crime cases and paternity disputes involve identical twins, scientists and court room personnel are doing their best and are optimistic regarding getting the method adopted into the legal system.

Early development of the embryos of identical twins begins with a single fertilized egg, however, they later acquire unique genetic mutations. When a fertilized egg starts to divide, there is a minor chance that the new cells can acquire a mutation. When the cells separate into the twin embryos, one will get the mutant cells and the other will get the remaining. This process then leads to each twin receiving different mutations. Therefore, identical twins are not genetically identical. New advances in DNA sequencing are allowing for these mutations to be identified and therefore make it possible to differentiate between identical twins. 

Just a single mutation, confirmed by this new method could be enough to implicate one twin over the other. For example, a laboratory in Brussels tested this method. They received DNA samples from identical male twin volunteers and of the one male's wife and child. The researchers sequenced the individuals' whole genomes  and discovered enough mutations to determine which male was the child's father and which was the child's uncle.

However, studies have concluded that in about 20% of the cases, mutations do not form. Additionally, the human genome possesses segments, known as short tandem repeats (STRs), that mutate quicker than the rest of our DNA. Due this fact, STRs tend to vary distinctively between individuals. 13 STRs have been identified that are effective in matching individuals to DNA samples.

If this method is adopted into the court systems, it could dramatically decrease the percent of wrongful convictions and aid the settlement of paternity disputes. This could be beneficial for the quality of life for the wrongful accused twin, the mother of a child or father of a child. There does not seem to be negative outcomes to this method.

Astronauts Mark and Scott Kelly Are Still Identical Twins, Despite What You May Have Read

Scott Kelly spent a year in space on the International Space Station while his identical brother, Mark Kelly, stayed on Earth. There was a lot of media confusion and over exaggeration on what happened after Scott Kelly returned to Earth, as he was examined to see what has changed in his body compare to his brother. Many were stating that they were no long identical twins because Scott Kelly’s DNA changed, however, that is not the entire case, they are still as much of twins before Scott Kelly went to space. Scott Kelly’s DNA did not change, but there are observations in changes in his gene expression, which changed by 7% because of the stresses from the different environments he was in like, scuba diving, mountain climbing and being in space. Furthermore, as the article states, “Although 93% of genes’ expression returned to normal postflight, a subset of several hundred ‘space genes’ were still disrupted after return to Earth.” Researchers focus on studying the genetic effects of the twins for future missions, like going to Mars, and to understand the long term effects of space travels. There are also lots of physical effects on the body that are being studied after traveling in space like weakening muscles, risks of cancer from being exposed to radiation and the overall stresses on the body. With the results, scientists can research and find solutions to improve the human body's health and well being while being in space.

I thought this article was very insightful and interesting pertaining to genetics in space studies because there isn’t much research material available. NASA has a great opportunity to study this case of twins with one being in a controlled environment and the other exposed to another extreme environment. I was also interested in this article because I am currently reading Scott Kelly’s book called, “Endurance, A Year in Space, A Lifetime of Discovery” that goes through his life, including his brother Mark Kelly, and all the way up to his experience on the International Space Station.

https://www.nytimes.com/2018/03/16/science/space/mark-scott-kelly-twins.html?rref=collection%2Fsectioncollection%2Fscience&action=click&contentCollection=science&region=stream&module=stream_unit&version=latest&contentPlacement=6&pgtype=sectionfront

https://www.nasa.gov/hrp/bodyinspace

Are gaze patterns affected by our genetics?

A study was done by Indiana University to test if eye movement, or gaze pattern, is controlled by genetics. The purpose of the study was to help us understand the differences between individuals’ gaze patterns and to see if they are influenced by genetics. Eye movement is an important thing to study because one of the first ways that we interact with our environment is through visual exploration. This study compared the gaze patterns of 233 pairs of twins (ages 9 to 14) of which about half were identical twins. The children’s gaze patterns were measured with an eye tracker which tracks movements in space and time. They also looked at how many features in the scene the children looked at, some only looked at one or two while others looked at many different features in the scene. They found similarities in the gaze patterns of both the identical and fraternal twins but saw much stronger similarities between the identical twins. They could match the correct twins using their gaze patterns, this is called gaze fingerprinting. The results support the hypothesis that the way we visually explore our environment is due to our genetics. 

This picture shows how the gaze patterns of twins were compared. They did not clarify if this was a set of identical or fraternal twins. I would have liked to have seen more pictures comparing identical twins, fraternal twins, and two unrelated people. I found it very interesting that they could identify a set of twins using their gaze patterns. It made me wonder what the similarities are between family members’ gaze patterns such as a parent and child. 

This is the link to the original paper that ScienceDaily used to write the article.

Practice May Not Make Perfect: Musical Ability is in The DNA

     

        I've heard people say before: "music runs in my family" and being a musician myself,  I found the idea quite interesting. When looking for an article, I found the headline: "Musical Ability is in The DNA" and within a matter of seconds, I was reading the article. A fascinating study was done in Sweden's Karolinska Institute by a doctor named Miriam Mosing. The question she had was concerning a person's musical abilities and if it has a strong connection to their genetic makeup. Is music ability due to practice time or DNA? 

       Together with her colleagues, Dr. Mosing studied 1,211 pairs of identical twins and 1,358 pairs of fraternal twins born between 1959 and 1985. Each individual was asked if they play an instrument or actively engaged in singing. If the answer was yes, she proceeded by asking the person to estimate how many hours a week he or she practiced at different ages and with that she calculated a score for their life's practice. Anybody who didn't play an instrument or sing got a score of zero. 

        Her next step was created to test a person's musical abilities. She had every person do the same exercises to test their pitch, appreciation of melody, and sensitivity for rhythm. These three areas were specifically chosen because expert musicians are exceptionally good at detecting differences within them. Most people expect that if someone puts in enough practice time, his music ability would be as high as an expert's; however, this assumption is false. In fact, it appeared to be no relationship between practice and musical abilities of the sort she was measuring. What I found amazing was a twin who practiced more than his genetically identical co-twin did not appear to have better musical abilities as a result. In another case, the difference between two such twins was 20,228 hours of practice. Surprisingly, the pair's measured musical abilities were found to be the same. 

        Dr. Mosing's findings, in no way, indicates that practice, has no value, but we can know that one with the "musical" genes have a really high chance of mastering such skills. In addition to this, her experiment showed music ability has a very strong genetic component which explains to me why I may here "music runs in my family" again.  

https://www.economist.com/news/science-and-technology/21606259-musical-ability-dna-practice-may-not-make-perfect

https://www.livescience.com/47205-musical-talent-genes-practice.html 

Being in space alters gene expression

Mark and Scott Kelly are Identical twins but they have one huge difference, one spent an entire year in space. early test results show that there is increased methylation in several genes this means that they are "turning off" and these affects are persisting for a short time while he gets reaclimated to being on earth. NASA scientists refer to leaving earths surface is akin to fireworks inside your body as you slip the surly bonds of earth. Many of Scott's genes activated and others turned off and we can see this by looking at the activation of his brother mark's genes while he remained on earth for the year. Also NASA is reporting that Scott's Telomeres grew while in space, could a gravity free environment influence telomerease in somatic cells? NASA is collecting this data to study the effects of a mars expedition and the affect prolonged space travel would have on humans.

the data collected from Scott's year in space could be pivotal to prolonged space travel for years to come and will help humans be successful in our endeavors into space. Its quite interesting that entering space the body starts to methylize certain genes, and activate others. Perhaps the most intriguing piece of evidence is the purported lengthening of Scott's telomeres, will this affect Scott's aging process? will he age slower than his brother? only time will tell.

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Genes affect where children look ; affects mental progress

A study led by Indiana university tested the eye movement of identical and fraternal twins, the study was conducted with 233 pairs of twins about half of each were identical and the other half fraternal. this results of this study have found that eye movements to complex social and nonsocial scenes are heritable.  Children were shown 80 images and tracked what are called "tendencies of exploration" and found that identical twins show a very strong link in their analysis of the images and the same affect was evident in fraternal twins but not as strong as the correlation in identical twins. The researchers suggest that their findings show that the basis of visual analysis of images is heritable

There are reasons to be skeptical of the findings of this study, there doesn't appear to be enough of a control in this situation their findings need to be followed up with analysis of random children from different areas/ and different environments, and have no correlation between those children to really prove a genetic  link between the eye movement.
link 1
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How Much of Autism is Genetic?

For a long time, autism wasn't understood well about where it comes from, and many people would argue. Nature vs. nurture: whether or not autism was a result of genetic makeup, or was a symptom of the environment (childhood experiences, vaccinations, etc). In a study published in the Journal of the American Medical Association, and reported by Time Magazine, genetics was stated to account for about 83% of the disorder. A number of different case study designs were utilized including the study of identical twins, non identical twins, siblings, and parent/child relationships. What the study concluded was that a substantial proportion of autism causation could be traced back to genetics and a child's DNA could eventually be used as a predictor for if and when autism presents itself. The research is still in it's infancy, as the study only reported on the correlation between certain gene features and the presence of autism. Even though this study provides valuable insight into the nature of autism, and could lead to earlier and better diagnosis, as well as better treatment and care for autistic people, it does open up new issues to be dealt with. Should babies get screened for autism? Could knowing you're having an autistic baby be a valid reason for abortion? The scientific value of this study is great, but what kinds of moral and ethical implications is it going to entail? I think that although this is great knowledge to have about the condition, it is going to be the beginning of new moral and ethical controversies, similar to those we've had in the past over Down Syndrome and the like.

Having Fraternal Twins May be Determined By your Genes

The deciding factor of twins may be in your genes. If you carry two specific genes in your body you are more likely to have fraternal twins. People with these genes tend to respond better to in vitro fertilization. Fraternal twins are are more closely related than identical twins. New research has shown that in vitro fertilization yields more twins than natural conception.  The first SNP is FSHB which is involved with the follicle stimulating hormone and the second is the SMAD3.  The SMAD3 changes how the ovaries respond to FSH and they believe that this is what creates the fraternal twins. The next research that they plan to do is with women that have SMAD3 and if they are more likely to get pregnant from in vitro fertilization.

I think that this is an amazing discovery.  People that have twins now have an answer as to why it happens to them. No one in my family has ever had twins so I know that I do not have these genes.

Gene to Increase Chances of Twins

After a study of 2000 mothers of fraternal twins, researchers have discovered that a woman's chance of having twins would increase if they have at least one of two genes through looking at their gene sequences. One gene affects the amount of hormone levels the mother has and the other is how the ovaries respond to them. Having just one copy of the SNPS would increase the chance of having fraternal twins by 29%. These SNPS are called FHB and SMAD3. FHB is the one that affects hormone levels and SMAD3 affects the ovaries response to FHB.

With this new information researches now have a better understanding of exactly what causes twins. This gives support that if the there are fraternal twins on the mother's side of the family, then there is a higher chance of her giving birth to a set of twins as well. Simply having the gene for twins does not necessarily mean the mother will give birth to twins, it only increases the likelihood. These genes in fact do not have to be present at all. So, there could be an "eve" gene for having twins, but it may have not been needed for the first set of fraternal twins to exist.