Sex-linkage (OCR A-level Biology A)

This fully-resourced lesson explores the inheritance of sex-linked diseases in humans and then challenges the students to apply their knowledge to examples in other animals. The detailed PowerPoint and associated differentiated resources have been designed to cover the part of point 6.1.2 (b[i]) of the OCR A-level Biology A specification which states that students should be able to demonstrate and apply their knowledge and understanding of genetic diagrams which include 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 carry out a dihybrid cross that involves a sex-linked disease and an autosomal disease before applying their knowledge to a question about chickens and how the rate of feather production in chicks can be used to determine gender.

All of the tasks are differentiated so that students of differing abilities can access the work and all exam questions have fully-explained, visual markschemes to allow them to assess their progress and address any misconceptions.