Understandings:

• Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed
• Gametes are haploid so contain only one allele of each gene
• The two alleles of each gene separate into different haploid daughter nuclei during meiosis
• Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles
• Dominant alleles mask the effect of recessive alleles but co-dominant alleles have joint effects
• Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles
• Some genetic diseases are sex linked
• The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes
• Many genetic diseases have been identified in humans but most are very rare
• Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer