Mitosis and Meiosis - Biology Department
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Transcript Mitosis and Meiosis - Biology Department
BSC 2010L
Prokaryotic Cells
Divide by binary fission
Produces “clones”
Only have to worry about 1 circular
chromosome
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 #)
Reproduction
◦ 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)
Humans
46 chromosomes
23 homologous pairs
○ Each pair:
1 came from mom, 1
came from dad
Ploidy
# 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!!!!!!
Meiosis
The purpose:
haploid
(1n) sperm
diploid (2n) zygote
haploid (1n) ovum
Meiosis
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?
Meiosis
At the beginning of meiosis, homologous
chromosomes find each other
This is where crossing over occurs
Gametogenesis in Animals
Spermatogenesis
Oogenesis
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
page
http://faculty.irsc.edu/DEPT/BiologicalSciences/mit%
20mei%20modelsHTML/index.htm
Use bead models to demonstrate
mitosis and meiosis