Genetic expression

 

Dominance is a description of genetic expression.  The various flower color variations are due to the degree at which the individual genes are expressing for this one trait.

Plants have two sets of chromosomes in their cells, each containing many genes in a sequence along its length. The ones in the same locations (facing each other) on both chromosomes control an expression. We call these genes alleles.

 

Diagram of chromosome showing alleles

 

Lets look at the color of flowers as an example.  When both dominant genes are the same RED/RED -you get red flowers!  Ditto for white (lack of pigment) – when both are equal WHITE/WHITE you get white flowers. 

 

Both alleles are the same for the trait of red color petals 

 

Dominant vs Recessive

 

Many times these alleles are not identical.  This is usually caused by a harmless mutation. Since they are related but not equal we call them variants.

The stronger one that actually has the trait expressed is termed “dominant”.  The less expressive one is called “recessive”.  In genetics both facing alleles have to be recessive for it to be expressed. In genetics, we call this phenomenon Dominance. 

 

Types of Dominance

 

Complete Dominance

When the alleles are mixed (different), RED/WHITE , then the stronger gene overrides the effect of the weaker and you get red flowers as well.  That is complete dominance!

 

Incomplete Dominance

When the alleles are mixed, RED/WHITE , and BOTH have a partial effect.  You get pink flowers.  That is incomplete dominance!

 

Both alleles are partially expressed

 
Co Dominant

When the alleles are mixed, RED/WHITE , and BOTH have a FULL expression.  You get flowers with both red and white parts.  That is co dominance!

 

Both alleles are fully expressed and independent

Over Dominant

When the alleles are mixed, RED/WHITE , and BOTH have an enhanced expression.  You get flowers with a more exaggerated color than that of the dominant one. That is over dominance – and it is very rare! The picture below is just for illustration.

 

Super red

 

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Article written by our Staff Horticulturist, Peter B Morris, BSc, MSc, MBA

All photographs used with permission @SHUTTERSTOCK