Essential idea: The inheritance of genes follows patterns.
The patterns that genes and the phenotypes they generate can be mapped using pedigree charts. The image above show a small section of a pedigree chart that maps the inheritance of hair colour in an extended family over several generations. Analysis of pedigree charts enables us to the nature of the inheritance; controlled by dominant or recessive alleles? linked to the sex chromosomes? controlled by multiple genes or a single gene?
Understandings, applications and skills
| 3.4.U1 | Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. |
| 3.4.U2 | Gametes are haploid so contain only one allele of each gene. |
| 3.4.U3 | The two alleles of each gene separate into different haploid daughter nuclei 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. |
| 3.4.U5 | Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects. |
| 3.4.U6 | 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.U7 | Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. [Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.] |
| 3.4.U8 | Many genetic diseases have been identified in humans but most are very rare. |
| 3.4.U9 | Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer. |
| 3.4.A1 | Inheritance of ABO blood groups. [The expected notation for ABO blood group alleles: O = i, A=IA, B = IB.] |
| 3.4.A2 | Red-green colour blindness and hemophilia as examples of sex-linked inheritance. |
| 3.4.A3 | Inheritance of cystic fibrosis and Huntington’s disease. |
| 3.4.A4 | Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl. |
| 3.4.S1 | Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. |
| 3.4.S2 | Comparison of predicted and actual outcomes of genetic crosses using real data. |
| 3.4.S3 | Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases. |
[Text in square brackets indicates guidance notes]
Starter
Gregor Mendel: Great Minds by SciShow - a high speed insight into the life of the 'father of genetics' by puppets!
Presentation and NotesThe presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.
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Weblinks
Mendel and Mendelian Genetics
Mendelian Inheritance by Wiley
Children resemble their parents by DNA From The Beginning
Practise questions on Inheritance
Sex linked inheritance problems by the biology project
Monohybrid inheritance problems by the biology project
Drag and drop genetics by ZeroBio
Drag and drop pedigree charts by ZeroBio (n.b. tongue rolling is not a true example of monohybrid inheritance)
Mendelian Inheritance by Wiley
Children resemble their parents by DNA From The Beginning
Practise questions on Inheritance
Sex linked inheritance problems by the biology project
Monohybrid inheritance problems by the biology project
Drag and drop genetics by ZeroBio
Drag and drop pedigree charts by ZeroBio (n.b. tongue rolling is not a true example of monohybrid inheritance)
Nature of science
Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data. (3.2)
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?
