Genes are portion of DNA.
Alleles are multiple version of the same gene -> allele 1, allele 2, allele 3.
Diploid cell are double content, Haploid are single content. With reproduction we get Diploid who by meiosis get gamets(haploid) that will merge with gamets of the other partner -> zygote == 1 + 1 = 2 diploid.
Heterozygous 1=2 and 1=1 or 2=2 Homozygous
Letters matter, Capital is strong dominant, Lowercase is recessive.
The possible combinations are genotypes.
Genotype frequences != Alleles frequences