1. Announcements SCI I, 407 M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,
● Tutoring Center
SCI I, 407
M 12-3, 5:30-6:30; W 8-9, 5:30-6:30,
Th 8-12, 6-7; F 8-9
● MasteringBiology Assignment due Tuesday 5/3
● Bring you textbooks to Lab this week 1

2. Cellular Reproduction
Cell division
Functions of cell division: *reproduction *growth and development *repair 2

3. Cellular Reproduction
In asexual reproduction:
Single-celled organisms reproduce by simple cell division
There is no fertilization of an egg by a sperm
FUNCTIONS OF CELL DIVISION
Asexual Reproduction LM
Amoeba
Sea stars
African Violet 3

4. Cellular Reproduction
Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis. 4

5. Eukaryotic ChromosomesLM 5

6. Eukaryotic Chromosomes
DNA double helix
Histones
The DNA in a cell is packed into an elaborate, multilevel system of coiling and folding.
Histones are proteins used to package DNA in eukaryotes.
Nucleosomes consist of DNA wound around histone molecules.
“Beads on
a string”
TEM
Nucleosome
Tight helical
fiber
Looped domains
Duplicated chromosomes
(sister chromatids)
TEM
Centromere 6

7. Chromosome Structure
Chromosome
Centromere
Sister Chromatids 7

8. chromosome duplication)
The Cell Cycle
S phase
(DNA synthesis;
chromosome duplication)
The cell cycle consists of two distinct phases
Interphase
Mitotic phase
Interphase
(90% of time) G1 G2
Mitotic
phase (M)
(10% of time)
Mitosis
Cytokinesis

9. Interphase G1: Metabolism and growth
Centrosomes
(with centriole pairs)
Interphase
G1: Metabolism and growth
End of G1: Cell signaled to divide
S (synthesis): DNA is duplicated
G2: Cell forms chromosomes, completes preparations for cell and nuclear division
Chromatin
Nuclear
envelope
Plasma
membrane LM

10. Prophase PROPHASE Early mitotic spindle Fragments of nuclear envelope
Centrosome
Centromere
Chromosome, consisting
of two sister chromatids
Spindle
microtubules
Figure 8.7.a

11. Metaphase, Anaphase, Telophase
Nuclear
envelope
forming
Cleavage
furrow
Spindle
Daughter
chromosomes

12. Cytokinesis
Animal cells Plant cells

13. Meiosis
Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis. 13

14. Meiosis Homologous chromosomes separate. Chromosomes duplicate. Sister
chromatids
separate.
Pair of homologous
chromosomes in
diploid parent cell
Duplicated pair of
homologous
chromosomes
Sister
chromatids
INTERPHASE BEFORE MEIOSIS
MEIOSIS I
MEIOSIS II 14

15. Meiosis MEIOSIS I: INTERPHASE Homologous pair up and exchange
Sister chromatids
remain attached
Pair of
homologous
chromosomes
INTERPHASE
Sister
chromatids
Homologous
pair up and
exchange
segments.
Chromosomes
duplicate.
Pairs of
line up.
split up.
Nuclear
envelope
Chromatin
Centromere
Microtubules
attached
to chromosome
Sites of
crossing over
Spindle
Centrosomes
(with centriole
pairs)
PROPHASE I
METAPHASE I
ANAPHASE I 15

16. Meiosis MEIOSIS II: SISTER CHROMATIDS SEPARATE Cleavage furrow
TELOPHASE II
AND
CYTOKINESIS
Sister
chromatids
separate
ANAPHASE II
Cleavage
furrow
TELOPHASE I
Two haploid
cells form;
chromosomes
are still
doubled.
MEIOSIS II: SISTER CHROMATIDS SEPARATE
PROPHASE II
METAPHASE II
During another round of cell division, the sister
chromatids finally separate; four haploid
daughter cells result, containing single
chromosomes.
Haploid
daughter
cells forming 16

17. Meiosis Cross over: How do we account for genetic variation?
*Independent assortment *Crossing over *Random fertilization
Independent Assortment: 17

18. Mitosis and Meiosis 18