Introducing ideas about inheritance
Class practical
It may help students in their future understanding of genetics to establish at an early stage the kinds of characteristics inherited and the kinds of characteristics influenced by environment.
Lesson organisation
This will depend on how much space you have in your teaching room, and whether you need to use another space to allow students to move around.
Apparatus and Chemicals
For each group of students:
(All optional)
Metre rulers
Tape measures
Mirrors
Health & Safety and Technical notes
There are no health and safety issues with this practical.
1 It is not essential that students' judgment of these features is correct, or that they measure the measurable variables. A rank order of ‘largest shoe size’ to ‘smallest shoe size’ is fine, as is ‘longest hand span’ to ‘shortest hand span’.
2 Refer to your current exam specifications and The Language of Measurement for guidance on terminology to use. It could be worth liaising with your maths department to find common ground in use of terminology for different variables.
Ethical issues
Avoiding features such as skin colour or body mass means you avoid some sensitive areas. Even height could be a sensitive issue for some young people. Sorting according to sex (male or female) should not be difficult. Be ready to react to any inappropriate remarks made about individual students.
Procedure
SAFETY: There are no safety issues involved in this work.
Investigation
a Ask students to sort themselves into groups or a line (Note 1) according to:
i the colour of their eyes
ii their handspan
iii the sport they like to play
iv their shoesize
v the languages in which they can count to ten
vi hair colour
vii the kind of music they prefer
viii male and female
b Discuss which criteria fall neatly into groups, and which require a ranking order. Define continuous variables and discrete/ categoric(al) variables (Note 2).
c Discuss which criteria students think are the result of their genetic make-up, their environment or a combination of factors.
d Discuss how students decide which features are genetically controlled. Rather than agreeing with a group consensus about cause, you could ask students to devise investigations to support their view or disprove an opposing view.
Teaching notes
Handspan and shoe size should readily become ranked characteristics – continuous variable ranging from maximum to minimum values in the group.
Although eye colour inheritance is not as simple as many text books and other references (even the BBC and the NHS websites) suggest, students will often sort themselves into groups according to eye colour – but there may be some that don’t fit so well into the group. If you are looking for good references on eye colour, choose those dating from after 2000, and even after 2006.
Hair colour may fall into groups. It is of course changed by environment if students have used hair colourants. They will need to decide as a group if this ‘counts’.
Preferred sport and music should again fall into groups, but students may argue that they like several kinds and so don’t fit into neat categories. 'Languages in which they can count to ten' is also likely to provide overlapping groups.
Male or female should form two definite groups. If you don’t want to get involved in conversations about sexuality or gender issues in this session, decide how you will deal with any that arise.
In terms of which characteristics are determined by genetics, students should be able to identify some characteristics which cannot be fundamentally changed – male/ female, eye colour and hair colour – although superficial changes to an individual could be made.
Some characteristics depend on environment – 'languages in which they can count to ten' will depend on which languages students have encountered. However you could argue that an ability to learn language and a skill level for learning language could be inherited.
Characteristics such as shoe size and hand span are determined by genetics but influenced to some extent by environment. Good nutrition and good health allow us to grow more quickly, and will mean these characters have a larger value than they might in other circumstances.
The sports and music we like are complicated characteristics which could be debated.
Health & Safety checked, September 2010
Web links
The Language of Measurement
ASE publication The Language of Measurement. Enables teachers to become confident about the special terminology associated with practical investigations, what terminology should be used, and what specific terms mean. The aim is for teachers, publishers, awarding bodies and others to have a common understanding of important terms arising from practical work in secondary science, consistent with the terminology used by professional scientists.
http://www.thetech.org/exhibits/online/ugenetics
Understanding Genetics: Stanford at the Tech is a site where geneticists from Stanford University answer questions about genetics posted to the site by students. The explanations are thorough and include significant technical detail. These include some explanations of the biology of eye colour and its inheritance.
(Websites accessed October 2011)