1. Introduction to Genetics
Chapter 9:
Genes & Cell Division

2. DNA Deoxyribonucleic acid Identified in the 20th century as the
genetic material
Chemical information storage
Daily function, development, and reproduction of all living things

3. DNA as information Sequence of 4 nucleotide bases: One “word” = gene
“letters” that spell amino acid sequence of proteins
One “word” = gene
DNA information is “read” and acted upon by other molecules (RNA, ribosomes)

4. DNA Backbone: (red) Bases: (blue & green) Double helix
Like a spiral staircase
Backbone: (red)
Repeating sugars & phosphates
“handrails”
Bases: (blue & green)
Adenine
Thymine
Guanine
Cytosine
“steps”

5. Genome Genome: Half comes from mom, half from dad
All of an organism’s genetic information
Half comes from mom, half from dad
Made of DNA packaged into chromosomes

6. Genome is a “library” Most cells carry the organism’s complete genome
Only some parts of it are in use
Different genes are expressed in different cells

7. The “library” is packaged in volumes called chromosomes
DNA is packaged
The “library” is packaged in volumes called chromosomes
Humans have 46
Chromatin: DNA wrapped & folded
around proteins

9. 46 chromosomes = 23 matched pairs
Homologous chromosomes:
A pair of chromosomes with genes for same types of proteins
Homologous is NOT identical
e.g., hair color
Paternal: brown Maternal: black

10. Karyotype

11. Cell Division to grow to replace dying cells
to adapt to changing needs
Uncontrolled cell division = CANCER

12. Cell Division Cell can’t just break in half
Must replicate the genome and precisely distribute it so each daughter cell gets the whole “library”

13. DNA replication
Mitosis
Cytokinesis

14. The Cell Cycle

15. Phases of the Cell Cycle
G1: normal cell life
S: DNA synthesis/replication
G2: preparation for cell division
M (mitosis): division of the chromosomes
G0: cells that don’t divide

16. one nucleotide at a time
S phase
Original DNA unwinds;
acts as template
for replication
New strands are
synthesized,
one nucleotide at a time

17. Chromatids Chromatin changes appearance:
Individual chromosomes are visible only after duplication
(DNA replication)
Chromatids

18. Telophase & cytokinesis
Phases of Mitosis M G1 S G2
Prophase
Metaphase
Anaphase
Telophase & cytokinesis

19. Mitosis: Prophase Chromatin condenses Nuclear envelope breaks down
Centrosomes: microtubule organizing centers

20. Mitosis: Metaphase Microtubules from the centrosomes form
mitotic spindle
Microtubules attach to
chromosomes and align
them at “equator”

21. Mitosis: Anaphase
The genome divides! Sister chromatids are pulled apart

22. Mitosis: Telophase & Cytokinesis
Nuclear membranes re-form
Chromosomes lose shape
Cytoplasm is split in half

23. Cell Division in Plant Cells
Only difference: cell can’t pinch in half

24. Prokaryotes: Binary Fission
No nucleus, only one chromosome