Why are Some Genes Dominant Over Others?

[2345qwert]

What makes a gene dominant over another? Like why is the gene for brown eye dominant over the one for blue eyes? My teacher says it is "just like that" but I'm not so sure. IS there a reason for this?

 

[Ryan_m_b]

A quick note on terminology: rather than saying genes are dominant over others it's best to say that different versions of genes (called alleles) are dominant or recessive over other versions. Dominance is not inherent to an allele meaning that there is nothing special about any allele that determines whether it is dominant or recessive. Rather it's the relationship between alleles because in some cases the phenotype of one allele "overrides" that of the other.

In the case of eye colour it's complicated because whilst students are taught in school that it's an example of simple dominance it isn't. Eye colour is determined by multiple genes which makes it more complicated. Keeping it simple though to illustrate the concept it's important to understand that pigment in the eye can accumulate both at the front and back of the iris. Genes that give rise to dark eyes cause pigment to appear in both layers however genes that cause light coloured eyes only allow pigment to form at the back. So if you imagine that you have one allele saying pigment should be at the back and one saying pigment should be at the front and back you end up with pigment in both areas.

Does this make sense?

 

[Ygggdrasil]

Here's a previous post on this topic that you may find useful:
https://www.physicsforums.com/showthread.php?p=3744324#post3744324

And here's a useful article on the subject:
http://genetics.thetech.org/ask/ask227

Let us know if you have any further questions after reading through this information.

 

[2345qwert]

A quick note on terminology: rather than saying genes are dominant over others it's best to say that different versions of genes (called alleles) are dominant or recessive over other versions. Dominance is not inherent to an allele meaning that there is nothing special about any allele that determines whether it is dominant or recessive. Rather it's the relationship between alleles because in some cases the phenotype of one allele "overrides" that of the other.

In the case of eye colour it's complicated because whilst students are taught in school that it's an example of simple dominance it isn't. Eye colour is determined by multiple genes which makes it more complicated. Keeping it simple though to illustrate the concept it's important to understand that pigment in the eye can accumulate both at the front and back of the iris. Genes that give rise to dark eyes cause pigment to appear in both layers however genes that cause light coloured eyes only allow pigment to form at the back. So if you imagine that you have one allele saying pigment should be at the back and one saying pigment should be at the front and back you end up with pigment in both areas.

Does this make sense?

Okay, but what causes this difference? I mean why do the genes for light eyes cause pigment to appear in just the back layer. And thanks for correcting my terminology!

 

[LudusRex]

The concept of dominant and recessive genes is a fundamental aspect of genetics and plays a crucial role in understanding how traits are inherited. A dominant gene is one that is expressed or observed in an individual, even if only one copy of the gene is present. On the other hand, a recessive gene is only expressed if an individual has two copies of the gene.

The reason some genes are dominant over others is due to the specific molecular structure and function of the gene. Genes are made up of DNA, which contains the instructions for making proteins. Proteins are essential for all biological processes and play a crucial role in determining an organism's traits.

In the case of eye color, the gene for brown eyes (known as the OCA2 gene) is dominant over the gene for blue eyes (known as the HERC2 gene). This is because the OCA2 gene contains instructions for producing a protein that is responsible for the production of melanin, the pigment that gives eyes their color. The HERC2 gene does not produce a protein that affects eye color, but rather it regulates the expression of the OCA2 gene.

So, when an individual inherits one copy of the OCA2 gene from one parent and one copy of the HERC2 gene from the other parent, the OCA2 gene will be expressed and result in brown eyes. However, if an individual inherits two copies of the HERC2 gene, the OCA2 gene will not be expressed, and the individual will have blue eyes.

In summary, the reason for the dominance of certain genes over others is due to their specific molecular structure and function, which ultimately determines how they are expressed in an individual. It is not a matter of one gene being inherently superior to another, but rather a result of the complex interactions between different genes and their corresponding proteins.