Question

How are genes responsible for cellular differences?

Answer 1

They aren't. All your cells contain your entire genome (with the exception of erythrocytes), \(\sf\color{red}{expression \;of \;certain\; genes\;is\;what\;makes\;cells\;(and\;tissues)\;differentiate}\) which is controlled by "epigenetics" this includes histones, regulatory sequences, patterns of acetylation, methylation, phosphorylation.