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3.4 Inheritance

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Description

Nature of science:
Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data. (3.2)
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 effects 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 and skills:
  • Application: Inheritance of ABO blood groups.
  • Application: Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
  • Application: Inheritance of cystic fibrosis and Huntington’s disease.
  • Application: 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.
  • Skill: Comparison of predicted and actual outcomes of genetic crosses using real data.
  • Skill: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
Guidance:
  • Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.
  • The expected notation for ABO blood group alleles is:
  Phenotype
    O
    A
    B
    AB		   Genotype
    ii
    |A| A or | Ai
    |B| B or | Bi
    |A| B
Theory of knowledge:
  • Mendel’s theories were not accepted by the scientific community for a long time. What factors would encourage the acceptance of new ideas by the scientific community?
Utilization:
Syllabus and cross-curricular links:
Biology
Topic 1.6 Cell division

Aims:
  • Aim 8: Social implications of diagnosis of mutations, including the effects on the family and stigmatization.

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