1. 9A:Inheritance and variation
Lesson 5: DNA, Chromosomes, genes, alleles

2. Learning objectives
Describe how genetic information is stored in the nucleus of cells
State the role of chromosomes, genes and DNA in heredity
Human cells have 46 chromosomes- gametes 23
Describe/draw the structure of DNA
Outline what happens during fertilization
2 gametes make one zygote which develops into the organism

3. Cell Nucleus
Contains all the DNA (deoxyribonucleic acid) for the organism
DNA molecules are made of chains of genes
DNA usually found as long strands but sometimes it coils up
When DNA is coiled scientists call it a chromosome

4. Nucleus-chromosome-DNA

5. Genes found on a chromosome

6. Alleles
Alleles are the different forms of a pair of genes

7. Chromosomes and Genes
Every individual has two copies of each chromosome, one from each parent therefore two copies of each gene
Most genes found on the chromosomes are the same but some are dominant and some are recessive which causes variations
Genes are the templates cells use to make proteins

8. In humans there are 23 pairs of chromosomes for a total of 46

9. DNA has a specific structure
Discovered by four important scientists
Double helix
4 nitrogenous bases form the rungs
Sugar and phosphate the backbone

10. Fertilization-gametes to zygote
Special cells with half the chromosomes which are created by the plant or animal (pollen, eggs)
Fertilization
When two gametes join together
Zygote
Name given to the first new cell of the organism

11. Tasks Draw/colour DNA worksheets DNA paper model (if available)
WS: 9Ac-3, 9Ac-1, 9Ac-5
p in (old)textbook