An alternative form of a gene is an allele. In a hybrid, a recessive allele is hidden but a dominant allele shows. A diploid organism has 2 alleles for each gene, a haploid gamete, just 1. A homozygote has two identical alleles of a gene, but a heterozygote has two different alleles of that gene.
Alleles segregate from each other in meiosis, but join randomly in fertilization.
A Punnett Square can predict the ratios of various genotypes and phenotypes from a mating.