3.4 Inheritance

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3.4 Inheritance

3.4 Inheritance

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Essential idea:

3.4.1  The inheritance of genes follows patterns.


Great resources with sets of activities about inheritance

Heredity in Families

Gender Testing of Athletes

Nature of science:


3.4.2  Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data. (3.2)




3.4.3  Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.


Heredity in families


Independent assortment  tutorial


 Alleles that do not assort independently


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


3.4.5   The two alleles of each gene separate into different haploid daughter nuclei during meiosis.


3.4.6   Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.


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


3.4.8   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.


3.4.9   Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes.


3.4.10  Many genetic diseases have been identified in humans but most are very rare. 


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




3.4.12  Application: Inheritance of ABO blood groups.


 Blood typing game


3.4.13  Application: Red-green colour blindness and hemophilia as examples of sexlinked inheritance.


3.4.14  Application: Inheritance of cystic fibrosis and Huntington’s disease.


3.4.15  Application: Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.


Fukushima's legacy: Biological effects of Fukushima radiation on plants, insects, and animals




3.4.16  Skill: Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.


Genetics Practice Problems


3.4.17  Skill: Comparison of predicted and actual outcomes of genetic crosses using real data.


 The Hardy Weinberg Principle


3.4.18   Skill: Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.

Pedigree simulation adress




3.4.19  Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.


3.4.20   The expected notation for ABO blood group alleles is:




Theory of knowledge:


3.4.21  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?





3.4.22  Syllabus and cross-curricular links:


Topic 1.6 Cell division




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

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