What Does Genotype Mean?

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What Is A Genotype?

Genes are, essentially, the blueprint of the way something looks, grows, behaves, and interacts with it’s surroundings – among other things. Genes can differ from other genes that do the same thing (eye color, for example) due to the way the nucleotides are arranged in the gene. These differences are called alleles. Where they’re located on the chromosome that contains that allele is called the locus. And because chromosomes occur in pairs, each organism have two alleles – one on each locus on each chromosome. 

When these two alleles “match” (ie: two blue eye genes) they’re called homozygous – homo meaning same in Greek. When the alleles are different (ie: one brown and one blue eye gene) they’re called heterozygous – hetero meaning different in Greek. In a situation where the alleles are heterozygous, the dominant gene will be displayed whereas the recessive gene is suppressed. In the case of incomplete dominance, both genes will be expressed to some degree determined on a separate allele. 

There are two camps genes largely fall into: phenotype (the result of the genes you can see) and genotype (the genes that influence the result of the phenotype.) Genotypes encompass the genetics of an animal or living creature as a whole – including the genes you can see as well as those you can’t – although genotype is generally only brought up when referring to genes you can’t see that interact with those that have expressions you can see, such as the extent of the expression of hetero- or homozygous. 


Examples Of Genotype

Let’s take the eye color example again, although it doesn’t apply to fish, I’m sure you’ll get the idea. Since eye color is incomplete dominant, the expression of each color will will present in some degree or another (hue, intensity, etc.) which will be controlled by another allele – which is another example of a geneotype genes.

eye color

Heterozygous Brown x Heterozygous Brown:

You can see each parent carrying one allele for blue and one allele for brown (making them both heterozygous) resulting in the following genotype possibilities:

  • Homozygous brown (two brown genes denoted as BB)
  • Heterozygous brown (one brown allele and one blue allele denoted as Bb)
  • Heterozygous blue (two blue alleles denoted as bb)

Heterozygous Brown x Homozygous Blue:

One parent is homozygous and carries two blue alleles (bb) while the other is heterozygous and carries one brown and one blue allele (Bb) which gives the following possibilities:

  • Homozygous blue (two blue alleles denoted as bb)
  • Heterzygous brown (one brown and one blue allele denoted as Bb)

When we says words like homozygous or heterozygous, we’re describing genotype genes. Additionally, when we show what genes they’re carrying that may be unexpressed (like Bb, where the blue is unexpressed) we’re talking about genotype genes, where the blue hiding in the genes is the genotype and the brown that is expressed is the phenotype. 

The genotype of animals can also be described as their “genetic potential” for something – color, fin shape, health, lifespan, intelligence – whatever, that may be influcenced (usually reduced) by environmental factors. This influenced capacity is the phenotype whereas the potential is the genotype. 

For example, a fish with genetics for bright blue coloration may never achieve anything other than dishwater dull if raised in poor conditions. 

Further reading & Sources

FAO.org – Selective breeding programmes or medium-sized fish farms

FAO.org – Inbreeding Depression

Technology Networks -Genotype vs Phenotype: Examples and Definitions

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