In the topic of inheritance it is easy to deliver conflicting information if not carefully planned. Students need to appreciate that for the majority of phenotypic features it is a combination of genes that give rise to this feature, yet in using genetic diagrams (punnett squares) it appears that a single gene codes for a single trait and that there are only two alleles for each gene.
Students often have misconceptions in relation to dominant traits, believing that this is most likely to be found in a population, rather than it being the one expressed over a reccessive trait in a particular individual. It is useful to refer to dominant traits that are rare in populations, such as Achondroplasia and Huntingtons disease.
When using Punnett squares it is important that students understand that these are probabilities and not fixed outcomes. The misconception that students demonstrate is that they believe that if there is a 1 in 4 chance of a couple having a child with a particular condition, if the first child has the condition, the other three will not. It is important to highlight that each child (however many children they have) has a 25% chance of having the condition. This can be linked to explaining sex determination- there is a 50% chance of having a boy or a girl. No matter how many children a couple have, if they have a boy first it does not change the probability of whether the next child will be a boy or a girl.
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