a normal somatic cell in diploid organims has two copies of each chromosome.
This means that there are two copies of each gene. These are known as alleles. Alleles can be dominant or recessive.
During meiosis, specialized germ cells are created which contain only 1 copy of each chromosome and are known as haploid. During the process of crossing over, the chromosomes are aligned and genetic information is shared between chromosomes. This process creates various new combinations within each germ cell.