The alleles of offspring vary, some are dominant and some are recessive, meaning that some traits get passed down and some don't, for example,: a dominant trait might be blue eyes, a parent would have blue eyes, and pass that dominant trait to their child so that the child would also have blue eyes, recessive traits are traits that skip a generation.
For example a grandparent might have black hair, but their child won't have black hair, however, their grandchild will have black hair, therefore the black hair trait is recessive and skipped a generation
Hope this helps