Essential Idea:
The inheritance of genes follows patterns
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
Applications:
- Inheritance of ABO blood groups
- Red-green colour blindness and haemophilia as examples of sex-linked inheritance
- Inheritance of cystic fibrosis and Huntington’s disease
- Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl
Skill:
- Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses
- Comparison of predicted and actual outcomes of genetic crosses using real data
- Analysis of pedigree charts to deduce the patterns of inheritance of genetic diseases