Sexual production (where offspring are produced through the union of gametes), creates offspring that are different from one another and either parent. Each unit of inheritance (called a gene), consists of a sequence of nucleotides at a specific place on a chromosome. All members of a species have similar (but not identical) nucleotide sequences. These slightly different nucleotide sequences in a gene are called alleles. When a mutation happens in the cells that produce eggs or sperm it may be passed down to generations. Sexual reproduction generates genetic variability between the members of a species: Eukaryotic chromosomes usually occur in pairs containing similar genetic information. Karyotype = complete set of chromosomes from a single cell. 2 chromosomes that make up 1 pair = homologous chromosomes. Homologous chromosomes contain the genes that control the same inherited characteristics. Diploids = cells with pairs of homologous chromosomes (meaning double) Diploids are made up of one maternal homologue + one paternal homologue.