A Genetic Mutation
The word ‘sport’ in botany, means a natural genetic mutation as a result of faulty chromosomal replication.
The sport results in a segment of the plant that is distinctly different from the parent plant in appearance (phenotype) and genetics (genotype)
A bud sport is the natural mutation that occurs in a single branch in a tree. In many cases the new character (trait) can be handed down to the plant’s offspring.
Many cultivated varieties of fruits are ‘sports’
For example the ‘Red D’Anjou’ is derived from the ‘Green D’Anjou’, and the difference is only in the skin colour;
‘Grand Gala’ and ‘Big Red Gala’ which are both derived from ‘Gala’ apple varieties.
The nectarine is also another example of a sport, which was derived from a peach.