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What Are Genotypes?

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  • Written By: Daniel Liden
  • Edited By: Bronwyn Harris
  • Last Modified Date: 10 July 2014
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Genotypes are the genetic makeups of organisms and are typically referred to with respect to the specific traits they describe. Genotypes exist in the form of genetic data such as DNA or RNA. While it is typically used to describe the genetic basis for a specific trait, the term genotype can also be used to represent the summation of a creature's genetic code. The term even applies to genetic information that is not expressed in some visible trait, as some genetic code is not actually observably expressed but is still a part of an organism's overall genetic information.

Genotypes are often studied in the fields of biology, biochemistry, and medicine because of their links to heredity. Parents pass many traits down to their offspring through their genetic data. Heredity can be explained through an understanding of the genetic code and the way that it is passed from parents to offspring. Traits are passed down through genes which are made up of two parts, or alleles. If the gene has a dominant allele, it will be expressed; if it has two recessive alleles, it will not be expressed.

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Different combinations of dominant and recessive alleles can lead to different results concerning the expression of a gene. Parents can pass down various combinations of alleles to their offspring, leading to certain traits being expressed or suppressed. The combination of alleles and genes present in organisms makes up their genotypes. Phenotypes, on the other hand, are the actual observable forms of the traits. Two alleles on a gene may determine that an individual has blue eyes; the alleles compose the genotype and the blue color is the phenotype.

The use of genotypes to understand heredity is particularly interesting because of the potential to predict and correct illnesses and disorders in individuals based on the genetic makeup of their parents. Many different disorders are clearly apparent based on an individual's genetic makeup. One disorder that is commonly predicted from a genetic basis is hemophilia, a disorder that inhibits the blood's ability to clot properly.

Many students of biology initially confuse genotypes and phenotypes, but the distinction is of the utmost importance. The genotype of an organism or specific trait refers specifically to the genetic information that describes a visible trait. A visible trait, such as eye color or hair color, can not be described as a genotype. Phenotype, on the other hand, specifically refers to those traits that can be described from observation. Genotypes are the factors that cause specific phenotypes to exist.

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Emilski
Post 4

When we were having our first child, we went to a person called a genetic counselor to make sure our child wasn't going to have any problems. Basically, she just took a sample of the blood and tissue from the child and tested it for different possible disorders. I don't know everything they check for, but I know they look for things like Down Syndrome. Fortunately, we had no problems.

Depending on how you look at the situation, it can be very helpful or stressful. If you find out that your child has no disorders and should be healthy, it is a relief. I can only imagine if the doctor came back and said that there was something wrong. It would put the parents in a tight spot about how they wanted to handle everything.

We didn't know about it at the time, but you can ever get testing before you plan to have a child. We did this for the second child. The doctor can take samples from both parents and give the probability of different situations. She described Punnett squares and how the different traits worked. Genetics are even advanced enough that once the child is developing they can tell you what its different features will look like. We chose to be surprised, though.

matthewc23
Post 3

@kentuckycat - You stumbled onto the same problems that it took scientists a long time to figure out. We still don't have all the answers.

As for the big toe issue, the answer is not necessarily. If a parent had a large toe, it means they either have two dominant alleles or a mix. If the other parent has a shorter toe, they have two recessive. Each child will have a 50% chance of having either kind of toe. Figuring it out is fairly simple. Look up Punnett tables for the explanation.

It is possible for different traits to be expressed using more than one gene. I believe eye and hair color are actually examples of this. You can even have situations where neither gene is dominant. The classic example is flower color. The other option is blood type where two alleles are dominant (A and B blood) and one is recessive (O). Genetics can be really interesting but really complicated depending how in depth you get.

kentuckycat
Post 2

@matthewc23 - Very interesting. I never really noticed it, but I guess I would have to have the recessive alleles. That got me thinking, though, if the dominant allele outcompetes the recessive, then if even one of your parents had the dominant genes where their big toe was larger, you would have to have it too, right?

I was wondering, too, is it ever possible for more than one gene to control a certain trait? How would you be able to predict what someone's children would look like in a situation like that if it is possible? And a final thing, what about something like eye or hair color where there is more than two different outcomes?

matthewc23
Post 1

I don't know if it is necessarily fair to say that dominant genes are expressed and recessive ones are not. In situations where an organism has two recessive alleles, the recessive trait is expressed in the phenotype.

As a matter of fact, there are quite a few traits in humans and other plants and animals where the recessive alleles are much more common, and that is the "normal" phenotype.

The one I specifically remember from my biology class for some reason is the length of your big toe. If you have one of the dominant alleles, your big toe is noticeably longer than your next toe. If you have two of the recessive alleles, your big toe is either about the same size or smaller than the one next to it. The recessive alleles are much more common, so most people have a smaller big toe.

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