Essential Idea:   The inheritance of genes follows patterns.
At SHS, Topic 3.4 is taught in the following class unit(s):​​​
3.4.U1  Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed.
  • Describe Mendel’s pea plant experiments.
3.4.U2  Gametes are haploid so contain only one allele of each gene.
  • Define gamete and zygote.
  • State two similarities and two differences between male and female gametes
3.4.U3  The alleles of each gene separate into different haploid daughter nuclei during meiosis.
  • State the outcome of allele segregation during meiosis.
3.4.U4  Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles.
  • Outline the possible combination of alleles in a diploid zygote for a gene with two alleles.
  • Outline the possible combination of alleles in a diploid zygote for a gene with three alleles.
3.4.U5  Dominant alleles mask the effect of recessive alleles but co-dominant alleles have joint effects.
  • Define dominant allele and recessive allele.
  • State an example of a dominant and recessive allele found in pea plants.
  • State the usual cause of one allele being dominant over another.
  • Define codominant alleles.
  • Using the correct notation, outline an example of codominant alleles.
3.4.U6  Many genetic diseases in human are due to recessive alleles of autosomal genes.
  • Define “carrier” as related to genetic diseases.
  • Explain why genetic diseases usually appear unexpectedly in a population.
3.4.U7  Some genetic diseases are sex-linked and some are due to dominant or co-dominant alleles.
  • Describe why it is not possible to be a carrier of a disease caused by a dominant allele.
  • Outline inheritance patterns of genetic diseases caused by dominant alleles.
  • Explain sickle cell anemia as an example of a genetic disease caused by codominant alleles.
  • Define sex linkage.
3.4.U8  The pattern of inheritance is different with sex-linked genes due to to their location on sex chromosomes.
  • Outline Thomas Morgan’s elucidation of sex linked genes with Drosophila.
  • Use correct notation for sex linked genes.
  • Describe the pattern of inheritance for sex linked genes.
  • Construct Punnett grids for sex linked crosses to predict the offspring genotype and phenotype ratios.
3.4.U9  Many genetic diseases have been identified in humans but most are very rare.
  • List five example genetic diseases.
  • Explain why most genetic diseases are rare in a population.
3.4.U10  Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
  • State two factors that can increase the mutation rate.
  • Outline the effects of gene mutations in body cells and gamete cells.
3.4.A1  Inheritance of ABO blood groups.
  • Describe ABO blood groups as an example of complete dominance and codominance.
  • Outline the differences in glycoproteins present in people with different blood types.​
3.4.A2  Red-green color blindness and hemophilia as examples of sex-linked inheritance.
  • Describe the cause and effect of red-green color blindness.
  • Explain inheritance patterns of red-green color blindness.
  • Describe the cause and effect of hemophilia.
  • Explain inheritance patterns of hemophilia.
3.4.A3  Inheritance of cystic fibrosis and Huntington’s disease.
  • Describe the relationship between the genetic cause of cystic fibrosis and the symptoms of the disease.
  • Outline the inheritance pattern of cystic fibrosis.
  • Outline the inheritance pattern of Huntington’s disease.
  • List effects of Huntington’s disease on an affected individual.
3.4.A4  Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
  • Outline the effects of radiation exposure after nuclear exposure at Hiroshima and Chernobyl.
3.4.S1  Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses.
  • Define monohybrid, true breeding, hybrid, F1 and F2.
  • Determine possible alleles present in gametes given parent genotypes.
  • Construct Punnett grids for single gene crosses to predict the offspring genotype and phenotype ratios.
3.4.S2  Comparison of predicted and actual outcomes of genetic crosses using real data.
  • Explain the reason why the outcomes of genetic crosses do not usually correspond exactly with the predicted outcomes.
  • Describe the role of statistical tests in deciding whether an actual result is a close fit to a predicted result.
3.4.S3  Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases.
  • Outline the conventions for constructing pedigree charts.
  • Deduce inheritance patterns given a pedigree chart.​
3.4.NOS  Making quantitative measurements with replicates to ensure reliability, Mendel’s genetic crosses with peas plants generated numerical data.
  • Outline why Mendel’s success is attributed to his use of pea plants.
  • List three biological research methods pioneered by Mendel.

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