Patterns of inheritance (6.1.2)
Navigate to resources by choosing units within one of the unit groups shown below.
Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Content: A clear outline of the content covered by the delivery guide
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject
- Thinking Contextually: A range of suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
Content (from A-level)
|6.1.2 Patterns of inheritance|
|(a)||(i) the contribution of both environmental and genetic factors to phenotypic variation
(ii) how sexual reproduction can lead to genetic variation within a species
|To include examples of both genetic and environmental contributions – environmental examples could include diet in animals and etiolation or chlorosis in plants.
Meiosis and the random fusion of gametes at fertilisation.
|(b)||(i) genetic diagrams to show patterns of inheritance
(ii) the use of phenotypic ratios to identify linkage (autosomal and sex linkage) and epistasis
|To include monogenic inheritance, dihybrid inheritance, multiple alleles, sex linkage and codominance.
To include explanations of linkage and epistasis.
|(c)||using the chi-squared (χ2) test to determine the significance of the difference between observed and expected results||The formula for the chi-squared (χ2) test will be provided.
M0.3, M1.4, M1.9, M2.1
|(d)||the genetic basis of continuous and discontinuous variation||To include reference to the number of genes that influence each type of variation.|
|(e)||the factors that can affect the evolution of a species||To include stabilising selection and directional selection, genetic drift, genetic bottleneck and founder effect.|
|(f)||the use of the Hardy–Weinberg principle to calculate allele frequencies in populations||The equations for the Hardy–Weinberg principle will be provided.
M0.2, M2.1, M2.2, M2.3
|(g)||the role of isolating mechanisms in the evolution of new species||To include geographical mechanisms (allopatric speciation) and reproductive mechanisms (sympatric speciation).|
|(h)||(i) the principles of artificial selection and its uses
(ii) the ethical considerations surrounding the use of artificial selection.
|To include examples of selective breeding in plants and animals
an appreciation of the importance of maintaining a resource of genetic material for use in selective breeding including wild types.
To include a consideration of the more extreme examples of the use of artificial selection to ‘improve’ domestic species e.g. dog breeds.
HSW2, HSW8, HSW10, HSW12
Detailed information on how species arise and the origin of new species. Includes key definitions on species.
The role of mechanisms including sympatric and allopatric speciation.
Approaches to teaching the content
The specification order would be the normal route, placing genetic crosses firmly in the context of events at meiosis and becoming familiar with genes and alleles in breeding crosses before looking at the effect of genes in populations in studying variation, evolution and artificial selection. Over a two year course there is the option to link the AS evolution unit with this one if desired.
A wide range of animal and plant examples can be introduced in the contexts of genetic crosses, variation, Hardy-Weinberg problems and case studies of speciation and artificial selection, adding to students’ appreciation of the range of diversity in the natural world and the species which are particularly important to us in agriculture. Some medical examples of genetic variation that impact on human health could also be included, for example haemophilia, and it is likely that students will encounter pedigree diagrams in this context. Various animals and plants are referenced in the links given in this delivery guide, including hypothetical ones (dragons and lumptys) which introduce a playful element that students tend to enjoy.
While solving crosses and equations with written symbols is one aspect, illustrating the scenarios with on-screen photographs of the phenotypes involved helps with contextual understanding and student motivation.
Common misconceptions or difficulties students may have
Students often find it hard to relate events at meiosis to what they are modelling when working out a genetics problem. They also have difficulty relating classical genetics, dealing with the inheritance of one of two genes, to both the biochemical level of molecular genetics, and even more so to the ecological level of population genetics.
The mathematical element of the chi-squared test and calculations using the Hardy-Weinberg equation cause problems for some, but with careful teaching and opportunities to practise and re-visit the process most should be able to grasp the techniques required.
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course.
2.1.3 Nucleotides and nucleic acids, is essential background for understanding genes and alleles in the age of molecular genetics.
4.2.1 Biodiversity, is supported by using a wide range of examples in teaching this section.
4.2.2 Classification and evolution, forms the background to 6.1.2 (d) to (h), and might need to be revised.
5.1.5 The animal responses section has a potential link to sympatric speciation where behavioural isolating mechanisms operate and different behaviours such as song are selected for.
6.1.3 Manipulating genomes, needs to relate to section 6.1.2 in building students’ conception of the link between chromosomes structure, genes, alleles and the base sequence of DNA.
6.2.1 The cloning topic involves reference to genetic variation and lack of it and so links with ideas encountered in 6.1.2 (a), (d) and (h).
Student worksheets and teacher sheets to download to develop understanding of meiosis and fertilisation. On this page there are also links to further worksheet-based resources on genetics, dragon genetics (problems concerning breeding hypothetical dragons with and without wings, horns, ability to breathe fire and short or long fangs) and blood type genes.
This page (see resource - Bottlenecks and founder effects (evolution.berkeley)) gives an idea for modelling population bottlenecks and the founder effect using bags of marbles. Coloured beads could also be used. The page is part of the comprehensive Evolution 101 website. Links to lesson plans occur at the foot of some webpages and there is a selection of teaching resources to explore (see tab at top of all pages). Further detail on bottlenecks and founder effects can be found in the second resource - Bottlenecks and founder effects (wallace.genetics).
Mechanisms of evolution are illustrated by graphics of beetles and the graphics can be downloaded as a separate file for incorporation into teaching materials.
M0.2, M2.1, M2.2, M2.3
The downloadable resources provide a complete guide to simulating evolution via a game where students place jelly bears of different colours on the Bear Island map and are dealt cards which affect bear survival due to selection pressures like disease, predation and competition. A more profound understanding of how environmental and ecological factors act as selection pressures should be achieved. A worksheet with sample answers is included.
Three references are given to support work on genetic and phenotypic variation in members of the Cucurbitaceae family, including research for wall posters and a long-term seed growing practical with a fun painting activity to finish.
A useful document on designing lab experiments to vary environment and genotype in fast-growing seedlings is referenced, to help design similar experiments customised for the apparatus available.
The fruit fly, Drosophila melanogaster, is an important model organism in genetics and a resource focusing on some of the common fly mutants is provided. Another model organism context for setting questions or research problems is the mouse (Mus musculus).
Principles of evolution and speciation are illustrated in three contexts in this list: bivalve molluscs, the family Canidae and Caribbean Anolis lizards. A variety of resources are provided at each site from which teachers can pick and choose.
Artificial selection references include dogs, maize and rare breeds of farm animals.
A good place to start to look at genetic contribution to phenotypic variation is an online seed catalogue. Thompson and Morgan offer a particularly large range, and the link given (see resource) lists 40 named genetic varieties of summer squash (Cucurbita pepo, including courgettes, marrows, patty pans and some small round pumpkins), winter squash (Cucurbita maxima, including giant pumpkins and squashes of different colours and shapes) and butternuts (Cucurbita moschata). As well as pictures of each variety there are descriptions focussing on traits such as disease resistance, storage capability and growth habit. Students could be asked to make a table comparing five different genetic variants of one species of Cucurbita, pinpointing the phenotypic variation between them.
Alternatively each student could choose the fruit or vegetable they like best and research it in the online seed catalogue, with a competition to see who can find the most different phenotypic varieties of one species, and the largest list of traits that vary. Work could be presented as wall posters featuring photographs of the genetic variants found.
Following on from the 'Pumpkin, Squash and Courgette Seeds' activity, if the work focuses on the phenotypic variation of Cucurbita it might be useful to have this list of Cucurbita genes with known alleles for reference. Table 1 lists all those known. Able students could highlight the genes they recognise from their seed catalogue work, e.g.
- Bl/bl for green fruit colour versus blue,
- Bu/bu for bush habit versus trailing and
- Wt/wt for warty fruit versus smooth.
Use could be made of these genes and alleles in practice work on genetic crosses.
PAG 6, PAG 9, PAG 11
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board and the decision to use them lies with the individual teacher. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for any errors or omissions within these resources. We update our resources on a regular basis, so please check the OCR website to ensure you have the most up to date version.
© OCR 2015 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the originator of this work.