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Heredity Theory

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Gregor Mendel pioneered heredity theory, proving that many physical traits can be passed on from generation to generation. These inheritable traits are dictated by DNA. Mendel explains heredity theory in the law of independent assortment and in the law of segregation.

Hereditary theory is the idea that many physical traits can be passed from one generation to the next by DNA, by passing on the set of instructions or genes in your DNA to your offspring. You pass on the physical traits that you possess yourself. And this is all based our modern understanding is all based on Mendel's work. Prior to Mendel, people had this idea that maybe there is blending going on. It is very complex and it just didn't match reality. But what he discovered is that with most traits you'll have dominant versions and recessive versions. And you'll typically get two copies of the a gene two alleles for every gene and how they interact with each other determines what physical traits you have.

Now since Mendel's time we've discovered that it's a lot more complicated than he initially thought. There's things like co-dominance where one and gene may share it's dominance with another gene etcetera. But one of the more complex things that help us better understand the world is that we learn that some traits are not controlled by one gene they're controlled by many genes. And a prime example of this is height.

Your height is determined not just by one gene say the amount of growth hormone that you produce but it's also influenced by the genes you have for the absorption of calcium. If you're lactose intolerant, you'll tend to drink less milk and so you'll be getting less calcium in your diet unless you get from other sources so that you won't be growing as fast because your your osteoblast the cells that build bones won't have as much building materials as somebody who's lactose tolerant.

There's also it's been discovered that your environment influences your genes. In lots of ways. One of the things that is recently been adapting a lot of modern understanding of genetics and inheritance is this idea of epigenetics. This is the idea that your environment right now, your diet etcetera it can actually cause some slight chemical changes to your DNA, not altering the sequence but adding groups and other things to other portions of the DNA. And you can apparently pass these modifications to your DNA for one or two generations past your own. So they have found that for example the diet of your grandmother while she was pregnant with your mum influences your body. Your metabolism and there's even some suspicion that it might even influence your intelect.

That's another thing that is really influenced by your environment. It is intelligence. You could have been the love child of Marilyn Vos Savant, the woman in the Guinness Book of World Records with the highest IQ and Albert Einstein. But if you spent your entire time just sitting and going sponge Bob and that's all you expose yourself to, those wonderful genes you have or intellect intelligence are going to go to waste. They have actually found that if you merely tell people that you can modify your IQ by doing certain things and that it is not as se- stable score that you get when you're born, they have found that people have been able to improve their IQ simply by being told that they can.

Other more common environmental influences that you'll see on biology tests are siamese cats. Their gene for pigmentation in their skin and in their hair is actually modified by the temperature and hot temperatures turns it off. Colder temperatures turns it on. That's why typically their paws, the tips of their ears ,their nose, their tip of the tail, the parts that get the coldest are the darkest while thir torso where it's warmer tends to be that lighter creamier color.

So these are some of the ways that in our modern understanding of heredity is shaped.