AP Biology class blog for discussing current research in Biology

Tag: Inheritance

Blame your Parents for your Stress?

Epigenetics is the study of inheritable changes in gene expression not directly coded in our DNA. Scientists at Tel Aviv University have shown that stress, induced by traumatic events, can be passed on to offspring. The study refers to this stress as passing on “memories.” The study finds the exact way that the inheritance of environmental influences is turned “on” and “off.” RNA sequences that regulate gene expression are partially responsible for deciding when the inheritance is on or off.

Scientists found that C.elegans worms only passed on inheritable epigenetic responses for a few generations (using small RNAs that target green fluorescent protein). This led them to believe that epigenetic responses die out eventually. However, this did not account for the possibility that inheritance could be regulated.  Scientists discovered that in order to create new small RNAs that allow a response to be passed on to multiple generations, they needed RdRP enzymes. These amplify heritable RNAs for generations. Certain genes that they called “MOTEK” (Modified Transgenerational Epigenetic Kinetics) were involved in turning on and off epigenetic transmissions. They switched on and off the small RNAs that the worms use to regulate genes using a feedback interaction between gene-regulating small RNAs and MOTEK. This determines whether an epigenetic memory will be passed on, and for how many generations.

Even though this study was done on worms, these scientists have said that these basics can possibly lead to discovery of inheritance for all organisms. This small bit of research can lead to endless amounts of knowledge for similar mechanisms in humans.

Overview of Epigenetics:

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How Old Are You, Polar Bear?


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Do you remember where mammals have DNA? (hint- it isn’t just in the nucleus)

Mammal cells have DNA in both their cell nuclei and their mitochondria. While DNA in the nucleus is a combination of both parents, mitochondrial DNA is inherited directly from the mother. (For more information about nuclear DNA and mitochondrial DNA download:…/dna-definitions.doc)

And what does this have to do with the age of Polar Bears?

Well, according to a recent article in the New York Times, scientists have been surprised to find that polar bears are not so closely related to brown bears as previously thought. For years, scientists thought that the polar bear specie evolved about 150,000 years ago. Adaptations, probably due to natural selection, include white fur and webbed paws – both of which are very helpful in the icy Arctic.

Researchers Axel Jenkle and Frank Haler, of the Biodiversity and Climate Research Center in Frankfurt studied 19 polar bears, 18 brown bears and 7 black bears. After analyzing the nuclear DNA of polar bears, they believe that brown bears and polar bears began taking different evolutionary paths as much as 600,000 years ago.

The old, incorrect, theory was based on mitochondrial DNA. The mitochondrial DNA of polar bears and brown bears are very similar.  Because polar bears live on ice, and there aren’t many fossils saved in the icy arctic, it has been difficult to trace the evolution of these famous white bears.

Now scientists are trying to figure out why the mitochondrial DNA of brown and polar bears is so similar. One hypothesis is that polar bears mated with brown bears during time of global warming or climate changes. There is some evidence of the bottleneck effect, which helps support this theory.


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Identical but Not the Same


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After studying genetically inherited traits and diseases it could be easy to assume that genes determine everything about us. While it is true that colorblindness is a sex-linked trait – there is certainly more to the story.

Monozygotic “identical” twins are genetically identical, so they should be the same in all ways shouldn’t they?

Why, then, does one twin get early onset Alzheimer’s disease and the other “identical” twin doesn’t? The same is true for height, autism, and cancer. Although, when one twin has a disorder the other is more likely to get the disease also, that is not always the case.

In the January edition of National Geographic, author Peter Miller discusses the newest theories about how genes, environoment and epigenetics affect our life (and the end of it).

Twins offer scientists a unique opportunity to study how genetically identical people differ. Basically, that means scientists can study how things other than genes affect human development and lifespan. Already, scientists have found that a persons height is only 80% determined by genetics because the heights of “identical” twins differ by about .o8 on average. Using IQ tests, scientists have nearly disproved John Locke’s Tabula Rasa or blank slate theory (the idea that children are born with a blank mind that is either stimulated – (and made intelligent) – or not –  (kept unintelligent)). Specifically, scientists studied twins who had been separated at birth and adopted into different families. In this way, scientists have found that intelligence  is about 75% controlled by genetics.

So that leads to the question, what is it besides genes that affects us humans so drastically?

Environment has something to do with our differences. However, that cannot be the whole story. “The Jim Twins” as they are called in the twin science community, were studied in the 1870’s. They were adopted into different families where both boys were named Jim. Then went on to have the same jobs, marry wives of the same name (two Lynda’s first then two Betty’s), enjoy the same hobbies, enjoy the same brand of cigarette and beer, name their sons James Allan and James Alan… the list goes on. These two lived very similar lives, yet they grew up in very different environments. If environment isn’t the only factor in creating difference then what is?

Scientists have recently come to believe that epigenetics plays a significant role in our lives. Epigenetics (site 2) can be seen as the meshing of environment and DNA. In the words of author Peter Miller “If you think of our DNA as an immense piano keyboard and our genes as keys – each key seach key symbolizing a segment of DNA respinsible  for a particulare note or trait, and all the keys combining to make us who we are – then epigenetic prcesses determine when an how each key can be struck changing the tune.”  Environmental changes do have some impact.  When a pregnant mouse is put under stress during the pregnancy it can create changes in the fetus that lead to abnormal behavior as the rodent grows into adulthood.

However, scarily enough, many epigenetic changes appear to occur randomly (thus creating a probelm for the organized nature/nurture theory). Currently work is being done studying DNA methylation, which is known to make the expression of genes weaker or stronger. Specifically, Andrew Feinburg, director of the Center for Epigenetics at Johns Hopkins School of Medicine, is working to find how DNA methylation relates to autism. Currently, he is using scanners and computers to search samples of DNA from autistic twins who have the disease in varying degrees. He is looking to compare how and why

the genes are expressed differently.

In the end, all we know is that there is more to our future than our genes can tell us. Yes, our genes play a huge role in who we are as people – in terms of appearance, character, intelligence and more – but there are some variables that our environment and epigenetics control.

Main Article: Miller, Peter. “A Thing or Two About Twins.” National Geographic. Jan 2012: 38-65. Print.

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