Whats the difference between a genotype and phenotype?

Asked on by maddy22

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trophyhunter1's profile pic

trophyhunter1 | College Teacher | (Level 1) Educator Emeritus

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A genotype is an organism's genetic makeup. In other words, what genes it has for a particular trait. For example, if you are referring the trait of height in a pea plant,  there are two different genotypes that can produce a tall pea plant. One genotype is TT ( the capital T stands for the tall gene or allele) therefore, two capital T's could produce a pure or homozygous tall pea plant. Another genotype for tall, is Tt (the capital T refers to a tall gene and the lower case t, a short gene). Although the plant has one of each type of gene for height, because the tall gene is dominant over the short gene, this will still produce a tall offspring. That is because the dominant gene (T)will be expressed and the recessive gene(t) will be hidden in this case. A third genotype exists for height in pea plants and that is two lower case t's, or tt. This genotype will produce a short pea plant.  To summarize, genotype is the pair of genes an organism has for a particular trait. 

Phenotype is the observable trait present in the organism. For example, if you were to see the pea plants in a garden, the TT and Tt will both appear tall.  And, if you saw the tt plant, it would appear short. So, basically  if a plant is TT or Tt, you will see both as tall plants and would have no way of knowing what genetic makeup each one had, through simple observation. 

Another example can be handedness in humans. There is the trait of right-handedness and left-handedness. The gene for right handedness is dominant over left handedness. Therefore, three genotypes exist- RR, RL, LL.  The person with a genotype of two R genes is a righty.  The person with a genotype with a righty and a lefty gene, RL is also a righty. That is because the right handed gene is dominant. The last genotype, LL is a lefty. The only way to produce the recessive left-handed person is two have to L genes. Therefore, there are three genotypes for handedness in people.

However, there are only two phenotypes:  A person is either a Righty or lefty.   

Question: Which person's genotype is always the same as their phenotype?


Answer: A lefty- if someone is a lefty(which is their phenotype), you always know their genotype must be LL!

pohnpei397's profile pic

pohnpei397 | College Teacher | (Level 3) Distinguished Educator

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The basic difference here is that one of these things has to do only with the way that an organism looks and one has to do only with what its genes are.

The phenotype has only to do with how an organism looks.  It is the outward appearance -- something that can be seen with the naked eye or at least without having to investigate the genes of that organism.  So my phenotype, for example, includes brown eyes.

The genotype has to do with what genes the organism has the causes it to have that particular phenotype.  If you remember your Punnett squares, my brown eyes (according to high school level biology, at least) could be caused by two dominant genes or it could be caused by a dominant and a recessive.  There is no way to know for sure in my case just by looking at my phenotype.

jk006's profile pic

jk006 | Student, Undergraduate | (Level 3) eNoter

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A Genotpye can be defined as: a group of organisms sharing a specific genetic constitution

A Phenotype can be defined as: what an organism looks like as a consequence of the interaction of its genotype and the environment

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