Identical twins are a rather unexplored subject in the world of genetics and biology. To if their creation is a genetic error to the many oddities of siamese twins, these similar siblings leave us with many questions. However, there is one question that was recently brought to our class’s attention that is so fascinating that it could change our understanding of heredity if answered. So far, it’s known that during conception, monozygotic or identical twins have 100% the same DNA. This means that all throughout their lives and even their children will share many genetic similarities.
However, what would happen if two sets of identical twins married each other and had kids, could these cousins actually be identical as well?
Through research, experiments, and the scientific method, we were able to find a surprising answer to this question. If you want to know what it is, read on and/or watch the video below.
Terminology:
Some helpful definitions of genetic terminology
1. Phenotype – The physical expression of a trait (ex. Brown Eyes)
2. Genotype – The genetic makeup of an individual (ex. The Gene for Brown Eyes)
3. Allele – A random variation of a specific trait that will define whether it shows up or not
4. Dominant Allele – An allele that would always show up in the phenotype when it is present in the genetic code
5. Recessive Allele – An allele that will only show up when no dominant alleles are present (2 recessive alleles need to be present)
6. Pedigree – A chart in which a family’s heritage can be mapped out (usually to show a gene being passed down)
7. Punnet Square – A chart that helps determine the odds of a child inheriting a certain gene
8. Gamete – A reproductive cell which contains half of a parent’s genetic information (sperm or egg)
9. Epigenetic Markers – Chemical markers which change the expression of genes
10. Heterozygous – Someone with one dominant allele and one recessive
11. Homozygous – Someone with either two recessive alleles or two dominant ones
Posing Hypothesizes
After learning about the mysterious case of the Sanders family (two sets of identical twins who married each other and one of the couples ended up having twin boys) and a little about chromosomes, my partner Morgan and I were able to come up with three hypothesizes that could be the answer to this question. I learned early on that keeping an open mind about this project was crucial because due to the lack of conclusive research elsewhere, there was a chance that any of the hypothesizes could be correct. We decided that:
A) The cousins could be perfectly identical as their parents are, so they will inherit 100% of the same DNA
B) The cousins could be genetically considered near identical, but a few factors would change their phenotype.
C) The cousins could not be considered identical because environmental factors would change their phenotype and genotype too much
We can find the answers to this through…
Research and Experimentation
We had our theories, and now it was time to prove them. Morgan and I dove head first into every study we could find about identical twins, genetics, and DNA. Starting off with the basic research we had from class, we were pretty sure that number 1 or 2 would be correct. It seemed only logical that if two identical twins who have the same DNA reproduce, their offspring would also be identical. However, we soon realized that this project was cleverly masked as something that we had to find a way to prove, but realized it was quite the opposite. This realization started with one simple fact:
Every gamete is unique
Every sperm or egg cell contains a random combination of each parent’s traits. Even if both parents have brown eyes, which is a dominant trait, (assuming they are heterozygous dominant), there is only a 75% chance their children would have them as seen below:
With this realization, we were compelled to look at the evidence even further to figure out if this could be plausible at all. We conducted in-class investigations where we mapped out punnet squares in groups and our own research we began to see that a single person has millions of alleles and for all of them to line up would be virtually impossible. Even if both parents are homozygous dominant for brown eyes (100% chance of both cousins having brown eyes), there is no guarantee any of the other traits would line up with this one. We also started to learn about epigenetic factors, which are chemical markers that change the expression of genes. These could occur if the pregnancies of the mothers were different, or through any amount of factors after birth such as UV rays from the sun, diet, exercise, and drug use.
Analyzing the Data
At this point, we had a lot of data. Some of it was useful, and some of it was useless. Some of it was even conflicting, which posed us with the task of analyzing our data. The project goal of this unit was to create a video that could clearly answer our inquiry question (see above), and we had a lot of simplifying and connecting to do if we were to complete this. With me working on making a script and Morgan the animation, we were able to successfully choose the most important and accurate facts and create a solid video. This part of the project did show me that I can still improve on teamwork because I feel we did not communicate our ideas well to each other when the video production phase began. I think I can improve on this by doing regular check-ins with my group and not immediately taking control if I think things won’t work out.
Conclusion
Despite our original beliefs, we ended up coming to the conclusion that hypothesis C was correct, meaning:
The cousins could not be considered identical because environmental factors would change their phenotype and genotype too much
This really solidified the importance of keeping an open mind with science to me as I realized your data could change at any moment. It also taught me the importance of thorough research, as I would have gone with the first theory if I hadn’t looked further into it. This will be a point of focus for me in the future because I wish to produce more scientifically and mathematically accurate results. I am really happy with the solid video production and increasing group efforts on my behalf, and am excited to see what our next Scimatics unit will entail.
Below is a Mindmap of what I have learned Everything in purple is something I didn’t know at the beginning of this unit:
Other Sources Used:
https://www.nytimes.com/2008/03/11/health/11real.htmlhttps://learn.genetics.utah.edu/content/epigenetics/twins/https://www.sciencedaily.com/releases/2015/11/151130141325.htmhttps://www.babymed.com/genetics/what-is-a-gene-mutationhttps://www.livescience.com/24694-identical-twins-not-identical.htmlhttps://genetics.thetech.org/ask-a-geneticist/twin-geneticshttps://people.com/movies/how-identical-triplets-separated-birth-twisted-adoption-experiment/https://youtu.be/owPC60Ue0BEhttps://www2.palomar.edu/anthro/mendel/mendel_1.htm