Inheritance

  • Mendel experiments with pea plants showing his rules of inheritance.

  • Gametes are haploid so contain only one allele of each gene.

  • The two alleles of each gene separate independently during meiosis.

  • Fusion of gametes results in diploid zygotes with two alleles of each gene.

  • Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects.

  • Many genetic diseases in humans are due to recessive, dominant or co-dominant alleles of autosomal genes.

  • Some genetic diseases are sex-linked, shown as superscript letters eg. Xh. The pattern of inheritance is different due to their location on sex chromosomes.

  • Many genetic diseases have been identified in humans & most are very rare.

  • Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.

SKILLS NEEDED:

  • Explain the inheritance of ABO blood groups.using IA, IB or i allele notation.

  • Explain inheritance of red-green colour blindness and hemophilia as examples of sex-linked inheritance.

  • Explain the autosomal inheritance of cystic fibrosis and Huntington’s disease.

  • Construct Punnett grids for monohybrid genetic crosses.

  • Compare predicted and actual outcomes of genetic crosses using real data.

  • Analyse pedigree charts and to deduce the pattern of inheritance of genetic diseases.