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- 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;
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BM5.1i extract and interpret information from charts, graphs and tables
BM5.1ii understand and use the concept of probability in predicting the outcome of genetic crosses
BM5.1iii understand and use direct proportions and simple ratios in genetic crosses
B5.1a explain the following terms: gamete, chromosome, gene, allele/variant, dominant, recessive, homozygous, heterozygous, genotype and phenotype
B5.1b describe the genome as the entire genetic material of an organism
B5.1c describe that the genome, and its interaction with the environment, influence the development of the phenotype of an organism to include use and examples of discontinuous and continuous variation e.g. eye colour, weight and height
B5.1d recall that all variants arise from mutations, and that most have no effect on the phenotype, some influence phenotype and a very few determine phenotype
B5.1e explain the terms haploid and diploid
B5.1f explain the role of meiotic cell division in halving the chromosome number to form gametes to include that this maintains dipliod cells when gametes combine and is a source of genetic variation
B5.1g explain single gene inheritance to include the context of homozygous and heterozygous crossing involving dominant and recessive genes
B5.1h predict the results of single gene crosses
B5.1i describe sex determination in humans using a genetic cross
B5.1j recall that most phenotypic features are the result of multiple genes rather than single gene inheritance
Learners typically have a good grasp of the key features of inheritance and some of the key terms used. This is rarely to the appropriate level however and they struggle to properly integrate the appropriate subject specific terminology into their work. Learners must fully understand these key terms (allele, phenotype, genotype etc.) and their appropriate use in order to achieve highly. Learners typically need significant practice in working out patterns of inheritance which by their nature gives them the exposure to and forces them to use specialist language.
Common misconceptions or difficulties learners may have
Learners have difficulty in relating DNA to genes, genes to chromosomes and then to cell structure. It is common for learners to struggle with the specialist language used for inheritance and genetics so some time given over to embedding this will be highly advantageous. Learners often mistakenly believe that all DNA mutations result in large changes to the organism as well as the notion that any instance of an additional chromosome will result in Down’s syndrome (rather than just an extra chromosome 21).
When asked the composition of DNA even at A level learners till have the misconception that it is made of protein.
Aide memoires can be useful as learning tools but one that is often used is haploid=half and diploid=double. Unfortunately this can lead students to assume that the normality is a pair of chromosomes and therefore haploid is one and diploid is four!
When asked for the probability of a heterozygous mating Aa x Aa resulting in a homozygous offspring, learners often state that the answer is 25%; the actual probability is 0.25.
Learners struggle with recognising that the key historical figures in the development of modern genetics did not have the same level of understanding that we do today. For example that Mendel did not know what DNA or even genes were. Typically this causes difficulty understanding why these figures were treated with scepticism.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
Learners enjoy taking the medical professional role with this topic. This links well to B3 well which contains similar health related content. Learners can be challenged to link mutations in DNA to the resulting effect on the individual.
Learners should collect continuous and discontinuous data from their classmates for analysis.
Learners should design and complete a table of results to collect data on shoe size, hand span, height, weight, ear shape and tongue rolling ability. These can then be presented graphically to show the difference in continuous and discontinuous data.
Approaches to teaching the content
Learners often complain of the lack of ‘relevance’ in biology to their lives. This is an ideal topic to put the specification content into a relevant context. Learners can be challenged to take the role of a genetic councillor, tasked with explaining the probabilities of passing certain traits from parents to their children in a family planning setting or in terms of solving paternity problems with blood type for example.
Learners use a range of food items such as onions or peas and extract the DNA from them.
This allows learners to visualise DNA as a thread like substance as well as considering how the method employed actually caused the DNA to be extracted and precipitated from the cell debris.
Learners compose an online profile page.
Design a social media page for the Gregor Mendel. In the page he should describe his work and show who his peers were at the time. Try to include some comments from his peers explaining why his work wasn’t as well received then as it is today.
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