1. DNA and Chromosomes

2. What Is a Chromosome? Chromo – means coloured. Some – means body.
They are not really coloured, but they take up cell dyes easily so they look coloured.
Chromosomes conists of a strand of DNA (Deoxyribose Nucleic Acid), wound around certain proteins.

4. What Is a Chromosome? A strip of DNA is a gene.
Chromosomes carry your genes.
Genes determine your shape, height, certain behavioural characteristics, and even whether you will get certain diseases.

5. Homologous Pairs
Each of us has 2 sets of chromosomes, called Homologous pairs.
One set came from your mother and one from your father.
These homologous pairs:
Are the same size.
Have their centromere in the same place.
Have the same genes in the same places (the same locus).

6. Homologous Chromosomes

7. Homologous Pairs of Chromosomes

8. Homologous Pairs
The actual expression of your genes depends on a combination of genetics working through your evolution, or family history.
If your ancestors lived in a desert area, you are likely to have a large nose, which can moisten the air before it hits the lungs.
If your ancestors lived in a cold, blizzard-swept area, you would probably have a small, squat nose.

9. Human Genome
Very soon we will know exactly which genes are on which chromosomes.
Teams of Scientists have worked out a map of the human genome.
Remember: a genome is the set of chromosomes in the nucleus of an organism).

10. Human Genome

12. Chromosome Number
A single set of chromosomes is called a Haploid number. It is given the symbol ‘n’.
A double set of chromosomes is called a Diploid Number. It is given the symbol ‘2n’.
Organisms can have more than 2 sets of chromosomes, this is called Polyploidy.

14. Chromosome Number Organism Chromosome No Alligator 32 Chimpanzee 48
Earthworm 36
Garden Pea 14
Dog 78
Redwood Tree 22
Fruit fly 8
Carrot 18
Cow 60

15. Human Chromosome Number
Humans have 46 Chromosomes: 23 from their mother and 23 from their father.
The human diploid number is 46 (body cells) and the haploid number is 23 (gametes).

16. Exception to the Rule
An exception to the rule that all homologous chromosomes are the same size are the sex chromosomes.
The females of most species are XX and the males of most species are XY.
All chromosomes other than the sex chromosomes are called Autosomes.
Human males have 22 autosomes + XY
Human Females have 22 autosomes + XX

17. Some Terms to Know
The total of an individual’s genetic material is called the Genome.
Organised into matching chromosomes, they are arranged into a Karyotype.

18. Female Karyotype

19. Male Karyotype