2. The life cycle of a cell Cell cycle consists of 2 major phases
Interphase, where chromosomes duplicate and cell parts are made
The mitotic phase, when nuclear division occurs
Figure 8.5

3. Metabolic activity is very high
Most of the life of a cell is spent in Interphase Cell does most of its’ growth during interphase
During interphase a cell performs all of its regular functions and gets ready to divide
Metabolic activity is very high
Figure 8.5

4. Untwisting and replication of DNA
Figure 10.4B

5. Before a cell starts dividing, the chromosomes are duplicated
Sister chromatids
This process produces sister chromatids
EM of human chromosome that has duplicated
Centromere
Figure 8.4B

6. Structure of Chromosomes
Homologous chromosomes are identical pairs of chromosomes.
One inherited from mother and one from father
made up of sister chromatids joined at the centromere.
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8. G2 Phase
This phase spans the time from the completion of DNA synthesis to the onset of cell division
Following DNA replication, the cell spends about 2-5 hours making proteins prior to entering the M phase
Figure 8.5

9. Centrosomes (with centriole pairs) Early mitotic spindle Centrosome
INTERPHASE
PROPHASE
Centrosomes (with centriole pairs)
Early mitotic spindle
Centrosome
Fragments of nuclear envelope
Kinetochore
Chromatin
Centrosome
Spindle microtubules
Nucleolus
Nuclear envelope
Plasma membrane
Chromosome, consisting of two sister chromatids
Figure 8.6

11. TELOPHASE AND CYTOKINESIS
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Cleavage furrow
Nucleolus forming
Metaphase plate
Nuclear envelope forming
Spindle
Daughter chromosomes
Figure 8.6 (continued)

15. Cytokinesis differs for plant and animal cells
In animals, cytokinesis occurs by cleavage
This process pinches the cell apart
The first sign of cleavage is the appearance of a cleavage furrow
Cleavage furrow
Cleavage furrow
Contracting ring of microfilaments
Figure 8.7A
Daughter cells

16. Cytokinesis differs for plant and animal cells
As the daughter chormosomes move to opposite poles
The cytoplasm constricts along the plane of the metaphase plate
The process of cytokinesis divides the cell into two genetically identical cells
Cleavage furrow
Cleavage furrow
Contracting ring of microfilaments
Figure 8.7A
Daughter cells

17. Chromosome distribution to daughter cells
When the cell divides, the sister chromatids separate
Chromosome duplication
Two daughter cells are produced
Each has a complete and identical set of chromosomes
Sister chromatids
Centromere
Chromosome distribution to daughter cells
Figure 8.4C

18. Multicellular diploid adults (2n = 46) Mitosis and development
The human life cycle
Meiosis is a special form of cell division that produces gametes
Haploid gametes (n = 23)
Egg cell haploid
Sperm cell haploid
MEIOSIS
FERTILIZATION
Diploid zygote (2n = 46)
Multicellular diploid adults (2n = 46)
Mitosis and development
Figure 8.13

19. Multicellular diploid adults (2n = 46) Mitosis and development
There is a special mechanism to produce gametes
Each gamete has a single set of chromosomes
22 autosomes and a single sex chromosome
Haploid gametes (n = 23)
Egg cell haploid
Sperm cell haploid
MEIOSIS
FERTILIZATION
Diploid zygote (2n = 46)
Multicellular diploid adults (2n = 46)
Mitosis and development
Figure 8.13

20. Gametes have a single set of chromosomes
Haploid gametes keeps the chromosome number from doubling in each succeeding generation
Haploid gametes are produced by a special sort of cell division called meiosis
Which occurs only in reproductive organs, ovaries and testes
Purpose of meiosis is to produce sperm and egg

21. MEIOSIS Meiosis involves 2 cell divisions
Meiosis produces 4 cells from 1 parental cell
Each of the 4 daughter cells has 23 individual chromosomes rather than 23 pairs of chromosomes
Meiosis reduces the chromosome number from diploid to haploid
Meiosis, like mitosis, is preceded by chromosome duplication
However, in meiosis the cell divides twice to form four daughter cells

22. PARENT CELL (before chromosome replication) Site of crossing over
MITOSIS
MEIOSIS
PARENT CELL (before chromosome replication)
Site of crossing over
MEIOSIS I
PROPHASE
PROPHASE I
Tetrad formed by synapsis of
homologous chromosomes
Duplicated chromosome (two sister chromatids)
Chromosome replication
Chromosome replication
2n = 4
Chromosomes align at the metaphase plate
Tetrads align at the
Metaphase plate
METAPHASE
METAPHASE I
ANAPHASE I
TELOPHASE I
ANAPHASE TELOPHASE
Sister chromatids separate during anaphase
Homologous chromosomes separate during anaphase I; sister chromatids remain together
Haploid n = 2
Daughter cells of meiosis I 2n 2n
No further chromosomal replication; sister chromatids separate during anaphase II
MEIOSIS II
Daughter cells of mitosis n n n n
Daughter cells of meiosis II
Figure 8.15

23. MEIOSIS I: Homologous chromosomes separate
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Centrosomes (with centriole pairs)
Microtubules attached to kinetochore
Sites of crossing over
Metaphase plate
Sister chromatids remain attached
Spindle
Nuclear envelope
Chromatin
Sister chromatids
Tetrad
Centromere (with kinetochore)
Homologous chromosomes separate
Figure 8.14, part 1

25. MEIOSIS II: Sister chromatids separate
TELOPHASE I AND CYTOKINESIS
TELOPHASE II AND CYTOKINESIS
PROPHASE II
METAPHASE II
ANAPHASE II
Cleavage furrow
Sister chromatids separate
Haploid daughter cells forming
Figure 8.14, part 2

27. Two equally probable arrangements of chromosomes at metaphase I
POSSIBILITY 1
POSSIBILITY 2
Two equally probable arrangements of chromosomes at metaphase I
Metaphase II
Gametes
Combination 1
Combination 2
Combination 3
Combination 4
Figure 8.16

28. Chromosomes are matched in homologous pairs
MEIOSIS AND CROSSING OVER
Chromosomes are matched in homologous pairs
Each synapsis is made up of 2 pairs of sister chromatids
This matched set of 4 chromatids is called a tetrad
Chromosomes
Centromere
Sister chromatids
Figure 8.12

30. Crossing over further increases genetic variability
Crossing over is the exchange of corresponding segments between two non-sister chromatids of homologous chromosomes
Genetic recombination results from crossing over during prophase I of meiosis
This increases variation further

31. How crossing over leads to genetic recombination
Coat-color genes
Eye-color genes
How crossing over leads to genetic recombination
Nonsister chromatids break in two at the same spot
The 2 broken chromatids join together in a new way
Tetrad (homologous pair of chromosomes in synapsis) 1
Breakage of homologous chromatids 2
Joining of homologous chromatids
Chiasma
Separation of homologous chromosomes at anaphase I 3
Separation of chromatids at anaphase II and completion of meiosis 4
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Figure 8.18B
Gametes of four genetic types

32. Coat-color genes
Eye-color genes
A segment of one chromatid has changed places with the equivalent segment of its nonsister homologue
If there were no crossing over meiosis could only produce 2 types of gametes
Tetrad (homologous pair of chromosomes in synapsis) 1
Breakage of homologous chromatids 2
Joining of homologous chromatids
Chiasma
Separation of homologous chromosomes at anaphase I 3
Separation of chromatids at anaphase II and completion of meiosis 4
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Figure 8.18B
Gametes of four genetic types