Page 50 - Science Coursebook

3.4 More about inheritance

Genes and chromosomes
Your genes are found inside the nucleus
of every cell in your body. The genes
are found on long threads called
chromosomes. Genes and chromosomes Each chromosome is a long chain of hundreds of
are made of a chemical called DNA. different genes.

Each gene is a set of instructions for the
cell. The gene tells the cell how to make a
particular substance. All the cells in your
body have the same genes, so they all have
the same sets of instructions.

For example, one of your genes has
instructions for making the pigment (colour)
of your hair. Another one has instructions for
making the shape of your nose.

Most genes have two or more different forms.
For example, the gene with the instructions
for making hair pigment in humans has

many different forms. There are forms that The gene that gives instructions for growing hair in
produce blonde hair, brown hair, red hair guinea pigs has two forms. One form produces smooth
hair, and the other produces rough hair.
and black hair.

Questions

1 In which part of a cell is DNA found?

2 Explain the difference between a gene and a chromosome.
3 Which form of the hair colour gene do you have?

Activity 3.4
Modelling genes and chromosomes

You are going to design and make a model of a cell containing chromosomes.
Here are some decisions to make before you begin.
• Will you make a 2D model (for example, sticking things onto a sheet of paper)
or a 3D model?
• How will you show the outside of the cell – the cell surface membrane?
• How will you model the nucleus of the cell?
• What will you use to model the chromosomes?
• How many chromosomes will you put into your cell?

• How will you show the different genes on the chromosomes?

48 3 Variation and inheritance

A+I A+E SE