An AAaa tetraploid plant will only produce a gamete which will be Aa, but during a self crossing a progeny with genotype AAaa will be produced and this will happen at a frequency of 35/36 and this simply means that the progenies produced during the self crossing will all have a dominant phenotype
The nerves in the integumentary system (skin) sense the irritation and send the signal to the brain. The brain then sends impulses through the nervous system to scratch the itch.
