A Punnett Square is a diagram used in genetics to predict the possible genetic outcomes of offspring from two parents.
The genetic makeup or set of genes in our DNA which determine various characteristics and traits.
The physical expression or characteristics of that genotype. It's what you see, such as hair color, eye color etc.
One version of a gene at a specific locus on a chromosome. For example, if there's a gene for eye color, blue eyes might be one allele and brown eyes could be another.