1. Chapter 3: Genes

2. Chromosomes
Are structures in the cell nucleus which carry
genes for inherited characteristics.

3. In pairs or groups of 3:
1) Draw a chromosome:
- are chromosomes in
pairs or are they single?
2) How many
chromosomes does each
human body cell contain?

5. Sex Cells
Sperm and egg cells
The 23rd chromosome pair are called the sex
chromosomes.
These are called sex chromosomes because
their genes determine the sex of the offspring.

6. Sex cells....
•
Male - X Y
When sperm cells are made they either contain an
x or a y. As well as the 22 other single
chromosomes.

7. Sex Cells...
Female - XX
Each ovum will contain an X and 22 other single
chromosomes.
white board picture.

8. QUIZ.............
If you are a boy would you have received an x
or y from your father?
You would receive an X chromosome from
your mother and a Y from your father.
If you are a girl would you have received an x
or y from your father?
You would receive an x from your father and
and x chromosome from your mother.

9. Dominant and Recessive Genes
Dominant: a gene for a particular
characteristic that completely masks the
recessive gene.
Recessive: a gene for a particular
characteristic that is masked by the dominant
gene.
Practice: white board.

10. Incomplete Dominance
Examples:
Black cat mates with a white cat and produces
a gray cat.
Blue bird mates with a yellow bird. All their
offspring are green.
neither gene is dominant or recessive. These
genes blend and mix in with each other.

11. If red is RR & white is WW. What is
the genotype of the F1
GENERATION?

12. Co-dominance
Both dominant genes are expressed.
Example: Human blood types.
Example whiteboard.

13. X- Linked Genes
This is because the Y chromosome is much
smaller than the X chromosome.
Colour vision and blood clotting.
Example on the board.Page 58,59 and 69 #
10

14. DNA and the genetic
code.
Chromosomes contain DNA. DNA makes up
the genes that determine your characteristics.

15. What makes up DNA?
sugars
phosphates
bases (nitrogen containing substances)
What are the four bases??????

16. In pairs or groups of 3:
Draw the structure of DNA; and
What is a triplet? What does this triplet code
for?
Page 62

18. Mutations

19. Mutations are alterations to genes.
Are all mutations bad?
Some mutations are detrimental to the
organism. However some mutations are
beneficial and some mutations are unnoticed.

20. Mutations occur naturally in our body, however
the rate of mutations can increase by exposure
to:
Nuclear reactors
UV sunlight
energy radiation from X-rays
exposure to chemicals - asbestos and certain
pesticides.

21. Human Genome
The human genome is the total genetic material in
a particular organism.