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BSC 2010L
Prokaryotic Cells
Divide by binary fission
 Produces “clones”
 Only have to worry about 1 circular
 Eukaryotic cells have many linear chromosomes,
requires organization, therefore mitosis is needed
Why do eukaryotic cells divide?
Growth and Repair
◦ Mitosis
 Produces 2 identical cells with same #
chromosomes (diploid #)
◦ Meiosis
 Produces cells with ½ chromosomes (haploid #)
Eukaryotic Cell Cycle
2 main phases
 Mitosis
 Interphase
○ Long period between cell division
 Some cells stay in interphase indefinitely
G1 is where the cell performs it’s “normal”
cell functions (may be days or years depending
on cell type)
 46 chromosomes
 23 homologous pairs
○ Each pair:
 1 came from mom, 1
came from dad
# of sets of chromosomes in a cell
 Haploid (n) – one set
○ Egg and sperm
 Diploid (2n) – two sets
○ All of our other cells
 Example:
○ In humans,
 Haploid # = 23
 Diploid # = 46
 These #’s will vary depending on the species!!!!!!
The purpose:
(1n) sperm
diploid (2n) zygote
haploid (1n) ovum
Humans have 46 chromosomes, 23
homologous pairs
 What is homologous?
 During Meiosis, it is VERY important that
one of EACH homologous pair ends up in
the gamete (sperm or egg)
 Why?
At the beginning of meiosis, homologous
chromosomes find each other
 This is where crossing over occurs
Gametogenesis in Animals
Notice how there
is 1 egg
What is Non-disjunction?
Onion Root Tip – Mitosis
Area of lots of cells undergoing mitosis in various stages
What you will see at 40x –
Have to magnify further to
See individual cells
Onion Root Tip - Mitosis
Identify stages – answers on next slide
Onion Root Tip - mitosis
Onion Root Tip - Mitosis
Identify stages
Onion Root Tip - Mitosis
Whitefish blastula - Mitosis
What you will see at 40x, each circle is a
Cross-section of the blastula, focus in
to see individual cells
Focus in on the individual cells
This is an example of anaphase
Lily meiosis in the anther
(production of pollen)
Differences between mitosis and meiosis
Mitosis is one division, meiosis is two
(meiosis I and II)
 Mitosis results in 2 identical daughter
cells, meiosis results in 4 haploid cells
 Homologous chromosomes find each
other before meiosis I
○ Crossing over occurs
Mitosis is for growth and repair, meiosis
is for reproduction
In this lab:
Observe microscope slides of mitosis
and meiosis
 Look at models of mitosis and meiosis
○ Tutorials of these models can be found on the
Biology Department Laboratory resources
Use bead models to demonstrate
mitosis and meiosis