Dominant and Recessive Traits

To understand basic terms in genetics, refer to our previous topic.

What are Dominant and Recessive Traits?

A trait is said to be dominant when it keeps appearing in each generation, while a trait is said to be recessive when they are present in an individual, yet they do not appear physically.

Dominant Traits:

If a dominant tall man, TT, marries a tall woman, who has a recessive trait for shortness, Tt, and they produce four children, all of them will be tall, meaning that the gene for tallness is dominant over the gene for shortness. 

This is demonstrated below:

∴ they are all tall.

Genotypic Ratio   =  2 : 2

i.e. 2 (TT) : 2 (Tt)

Phenotypic Ratio  = 4 : 0

i.e. 4 tall offspring, 0 short offspring

Recessive Traits:  

If a tall man, TT, marries a short woman, tt, they may not produce any short child or children, but the children having the recessive traits may produce short children by the second generation. 

This is illustrated below:

Genotypic Ratio = 4 : 0

i.e. 4 (Tt)

Phenotypic Ratio = 4 : 0

i.e. 4 tall offspring

However, in the second generation, short children can be produced. 

This is illustrated below:

Genotypic Ratio = 1 : 2 : 1

i.e. 1 (TT) : 2 (Tt) : 1 (tt)

Phenotypic Ratio = 3 : 1

i.e. 3 tall offspring and one short offspring