This is a fully-resourced lesson which looks at the inheritance of genes that are carried on the sex chromosomes in sex-linkage. Students will explore sex-linked diseases in humans and then are challenged to apply their knowledge to examples in other animals. The detailed PowerPoint and associated resources have been designed to cover the second part of point 3.8 (ii) of the Pearson Edexcel A-level Biology (Salters Nuffield) specification which states that students should understand sex-linkage.
Key genetic terminology is used throughout and the lesson begins with a check on their ability to identify the definition of homologous chromosomes. Students will recall that the sex chromosomes are not fully homologous and that the smaller Y chromosome lacks some of the genes that are found on the X. This leads into one of the numerous discussion points, where students are encouraged to consider whether females or males are more likely to suffer from sex-linked diseases. In terms of humans, the lesson focuses on haemophilia and red-green colour blindness and a step-by-step guide is used to demonstrate how these specific genetic diagrams should be constructed and how the phenotypes should then be interpreted. The final tasks of the lesson challenge the students to apply their knowledge to a question about chickens and how the rate of feather production in chicks can be used to determine gender.