Cambridge Secondary (7-9). Stage 9. Science. Learner's Book - Unit 7: Genes and inheritance

Atoms and cells both contain a nucleus. Why do you think these very different structures have the same name? Discuss with a partner, then share your ideas.

Which one is larger: the nucleus of a cell or the nucleus of an atom?

What does the nucleus of a cell do?

Making models of chromosomes in a cell. Work in a group of two or three. Choose an animal species and use the internet to find how many chromosomes its cells have. Use any materials, such as string or wool, and a large sheet of paper. Draw a freehand cell outline (not a perfect circle) and a large nucleus. Make two of each kind of chromosome: for example, 32 chromosomes need two sets of 16. Stick them inside the nucleus and write a heading naming your animal species.

Explain why we cannot usually see the chromosomes in a cell, even using a microscope.

Red blood cells do not contain a nucleus. Do you think they contain any chromosomes? Explain your answer.

Explain the difference between a chromosome and a gene.

All fruit flies have a gene for wing shape, in the same place on their chromosome 2. But some fruit flies have normal wings, and some have very tiny wings – so small that they cannot fly. What can explain this?

All cells have similar features, but most kinds of cell are specialised to perform a particular function. How many different kinds of animal cells can you think of?

What features do the different kinds of animal cells all share?

Can you describe how some animal cells are adapted for their functions?

What is a gamete?

Draw a table with two columns. Write the headings “Sperm cell” and “Egg cell” at the top of the columns. Then make a comparison of these two cells. Try to think of at least three differences between them.

Modelling sex inheritance. Work in pairs with two containers, 45 same-colour pieces of string or wire representing X chromosomes, and 15 equal-sized pieces of a different colour representing Y chromosomes. Put 30 X pieces in the egg container, and 15 X plus 15 Y pieces in the sperm container. Without looking, take one piece from each container to make a zygote. Repeat until all pieces are used.

The egg pot contains 30 X pieces; the sperm pot contains 15 X and 15 Y pieces. Draw one piece blindly from each pot without replacement until all 30 pairs have been used. For each draw in the sex-inheritance model, write down the chromosomes in the zygote (fertilised egg) you have produced. Record the result in a table.

The egg pot contains 30 X pieces; the sperm pot contains 15 X and 15 Y pieces. Draw one piece blindly from each pot without replacement until all 30 pairs have been used. When you have used up all the chromosomes in the sex-inheritance model, add up the total numbers of female and male zygotes you have produced.

The egg pot contains 30 X pieces; the sperm pot contains 15 X and 15 Y pieces. Draw one piece blindly from each pot without replacement until all 30 pairs have been used. From your results in the sex-inheritance model, what can you say about the chance of a baby being a boy or a girl?

Is it correct to say that the sex of a baby is determined by its father, not its mother? Explain your answer.

Explain, in your own words, why the numbers of boy and girl babies born each year is approximately equal.

In Stage 7, you learnt what a species is. Think of a way to complete this sentence. Try to include some useful scientific information in your sentence. A species is … .