3 Oct

You get it from your Mamma!

How many of you have heard this? You know that the person is saying you get some trait, whether it is physical in appearance or some habit, from your parents. But do you know how you got said trait from that parent?

Today, we are going to discuss gene inheritance.

A gene is a piece of DNA that encodes for a particular trait. Eye color, hair color, height – these are all traits that are decided by your genetic makeup. Inheritance is just the passage of this genetic information from the parents to the offspring, you. To understand how inheritance works, we need to learn some history in genetics (the study of genes and their inheritance).

Mendelian Genetics

Between 1856 and 1863, a man named Gregor Mendel performed numerous genetic experiments using pea plants. He would selectively breed pea plants together and discovered that certain traits show up in offspring without blending the parent characteristics. Some examples are seed shape (round vs. wrinkled), flower color (purple vs. white), and seed color (yellow vs. green). Illustrated below is an example of how the trait for purple flower color is inherited.

By Madprime - Own work, CC BY-SA 3.0
Flower color inheritance

The purple color is what is known as a dominant gene, or a gene who’s phenotype is expressed if a single copy of the gene is present. We represent dominant genes by a capital letter. The white flower color is a recessive gene, or one who’s trait is masked unless both versions of the gene are the recessive gene. We represent recessive genes by a lower case b. In the illustration above, we are mating a female plant with a male plant that both have one copy of the dominant allele and one copy of the recessive allele. During formation of the gametes (sex cells that in humans are the egg and sperm), the cell will inherit one copy of the flower color gene, either the B or the b. Once the male and female gametes fuse together after mating of the plants, there are four possible outcomes:

  • The new plant receives two B copies, one from each parent
  • The new plant receives a B from mom and a b from dad
  • The new plant receives a b from mom and a B from dad
  • The new plant receives two b copies, one from each parent.

The result is that the offspring plant has a 75% chance of being purple. This percentage is because in three of the four combinations, at least on B copy was inherited. In the case of inheritance of bb, then the flower will be white.

Humans are more complex than plants

In humans, inheritance of genes occurs in the same manner. We have several traits that are either dominant or recessive. We also have several traits that are controlled by more than one gene. An example is eye color.

Eye color inheritance.

As you can see, eye color is more complex inheritance than flower color because there are two genes involved in deciding eye color.

Disease and Inheritance

What has become the new “it” subject in genetics is the link between genes and disease. This link can be the inheritance of specific diseases such as sickle cell anemia to the inheritance of the risk of disease such as cancer. One topic that is of personal interest is the inheritance of mental health diseases such as depression or anxiety.

A study in 2013 funded by the National Institute of Health (NIH) found that five major health illnesses are traceable to the inheritance of genetic variations. These include schizophrenia, bipolar disorder, depression, ADHD, and autism. The authors were clear to point out that the genes put you at risk of the illness but does not mean you have the disease.

So what exactly does this mean?

Well, if one of your parents has depression, like my mother, you are more likely also to have depression than a person who’s parents do not have depression. Does this mean my mom is at fault for my depression? NO!!! She inherited the gene from one of her parents just like I did. Thankfully with today’s medicine, most of this illness can be controlled.

 

Special thanks to my mom for the idea for this post! If you have questions or comments, please reply below!

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