1. CHROMOSOMES

2. How is DNA stored?
All of the DNA in one human cell is 3 meters long end to end!
A single cell is microscopic – how does that much DNA fit??

3. Chromatin DNA is wrapped around proteins Molecule is more compact

4. Chromatin Chromatin can be loosely or tightly coiled
Loose = active genes, lots of transcription
Tight = less active genes, little transcription

5. Histones The proteins around which DNA is coiled to form chromatin.
Grouped into units of eight histones (AKA octamer)
Each unit of a histone octamer and its DNA is called a nucleosome.

6. Chromosomes A form of DNA storage
Chromatin is coiled to make a chromatin fiber
Fibers are looped and coiled to make dense tube-shaped structures

7. Chromatin vs. Chromosomes
Chromatin is how DNA is stored for most of a cell’s life
Need easy access to active genes for making proteins
Chromosomes form just before a cell divides
Easy to sort and separate when in compact units

8. Parts of a chromosome
Centromere = specific genetic sequences marking the center of the chromosome
Telomeres = specific genetic sequences marking the ends of the chromosome

9. How many do we have?
What’s your guess?

10. How many do we have?
Humans have 23 PAIRS of chromosomes (46 total)

11. How many do we have? Humans have 23 PAIRS of chromosomes (46 total)
Mouse = 20 pairs
Chicken = 39 pairs
Tomato = 12 pairs

12. How many do we have? Humans have 23 PAIRS of chromosomes (46 total)
Mouse = 20 pairs
Chicken = 39 pairs
Tomato = 12 pairs
Do you think that having more chromosomes means you are a more complex organism? Why or why not?

13. Why pairs?
Why is it that chromosomes can be paired together?

14. Why pairs?
One chromosome from Mom and one from Dad!

15. Why pairs? One chromosome from Mom and one from Dad!
Homologous chromosomes = chromosomes that share the same sets of genes but the genes may have different variations
EX: these chromosomes both have the hair color gene but mom’s chromosome is for brown hair and dad’s chromosome is for blond hair.

16. Sex chromosomes
X and Y
Females have ________
Males have ________

17. Sex chromosomes
X and Y
Females have XX
Males have XY

18. Chromosomes & Evolution

19. EXIT TASK
What do you call the proteins around which DNA wraps itself to form chromatin and chromosomes?