Cell Reproduction
Cells Division Introductory Video
The Chromosome
•During cell division the cell’s DNA is coiled compactly into a CHROMOSOME
•Each chromosome is a single DNA molecule
•The DNA wraps tightly around a protein called HISTONE (helps maintain the chromosome’s shape)
Breaking Down the Definitions1. Chromosome2. Histone3. Chromatid4. Centromere5. Chromatin6. Sex chromosome7. Autosome8. Homologous
chromosome9. Karyotype10. Diploid
11. Haploid12. Binary fission13. Mitosis14. Asexual reproduction15. Meiosis16. Gamete17. Interphase18. Cytokinesis19. Prophase20. Spindle fiber
21. Metaphase22. Anaphase23. Telophase24. Cell plate25. Synapsis26. Tetrad27. Crossing over28. genetic recombination29. Independent assortment30. Sexual reproduction
Anatomy of a Chromosome• Each half of a chromosome is
called a CHROMATID• Chromatids form as the DNA
copies itself before cell division• The 2 Chromatids are attached at
a point called a CENTROMERE• CHROMATIN=less tightly areas of
DNA between cell divisions
Chromosome Numbers• Every species has a certain number of
chromosomes in each cell.• Animal chromosomes are either:
• Sex Chromosomes—will determine the gender of an organism (X and Y)
• Autosomes—all of the other chromosomes
• Cells with 2 sets of Chromosomes are DIPLOID
• Cells with one set of chromosomes are HAPLOID (sex cells…half the number of chromosomes)
Chromosomes Clip• How many chromosomes does a potato have?
• How many chromosomes do Ferns have?
• After the video…in your own words why do different organisms have different numbers of chromosomes??
Cell Division (aka Cell Reproduction) in Prokaryotes•Most prokaryotes reproduce by BINARY FISSION
•2 identical cells are produced from one cell
•Draw this
Cell Division Eukaryotes• Two types of Cell Division
(Reproduction) in Eukaryotes!• Mitosis=new cells with
identical genetic material• Meiosis=reduces the number
of chromosomes by half for the purpose of eventual reproduction
Mitosis
Meiosis
The Cell Cycle•The CELL CYCLE is the repeating events of the life of a cell.
• Interphase is the period between cell divisions
How do little elephants grow up to be BIG elephants?
Three reasons why cells reproduce by asexual reproduction or MITOSIS:
1. Growth 2. Repair 3. Replacement
Mitosis Cycle
• Interphase• Prophase• Metaphase• Anaphase• Telophase & Cytokinesis
Interphase occurs before mitosis begins
• Chromosomes are copied (# doubles)• Chromosomes appear as threadlike coils (chromatin) at the
start, but each chromosome and its copy(sister chromosome) change to sister chromatids at end of this phase
CELL MEMBRANENucleus
Cytoplasm
InterphaseAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Prophase 1st step in Mitosis
• Mitosis begins (cell begins to divide)• Centrioles (or poles) appear and begin to move to opposite
end of the cell. • Spindle fibers form between the poles.
CentriolesSister chromatids
Spindle fibers
ProphaseAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Spindle fibers
Centrioles
Metaphase 2nd step in Mitosis
•Chromatids (or pairs of chromosomes) attach to the spindle fibers.
Centrioles
Spindle fibers
MetaphaseAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Anaphase 3rd step in Mitosis
•Chromatids (or pairs of chromosomes) separate and begin to move to opposite ends of the cell.
Centrioles
Spindle fibers
AnaphaseAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Telophase 4th step in Mitosis
• Two new nuclei form. • Chromosomes appear as chromatin (threads rather than
rods).• Mitosis ends.
NucleiNuclei
Chromatin
TelophaseAnimal Cell Plant Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Cytokinesisoccurs after mitosis
•Cell membrane moves inward to create two daughter cells – each with its own nucleus with identical chromosomes.
Animal Mitosis -- ReviewInterphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- ReviewInterphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
REMEMBER!InterphaseProphaseMetaphaseAnaphaseTelophaseCytokinesis
IPMATC
I P___ M___ A___ T___ C______
Label it!
Brainpop Mitosis
Mitosis in an Onion
Prophase
Metaphase
Anaphase
TELOPHASE and CYTOKINESIS
Stages of Mitosis Animation
It’s your turn! Identify the stages of mitosis…
Mitosis Dance Video
Onion Tips and Whitefish…
View 1 View 2 View 3 View 4 View 5
Whitefish
Onion
Meiosis KM 42
Meiosis – key differences from mitosis
• Meiosis reduces the number of chromosomes by half.• Daughter cells differ from parent, and each other.• Meiosis involves two divisions, Mitosis only one.• Meiosis I involves:
• Synapsis – homologous chromosomes pair up. Chiasmata form (crossing over of non-sister chromatids).
• In Metaphase I, homologous pairs line up at metaphase plate.• In Anaphase I, sister chromatids do NOT separate.• Overall, separation of homologous pairs of chromosomes, rather
than sister chromatids of individual chromosome.
Meiosis I (four phases)• Cell division that reduces the chromosome number
by one-half.
• four phases:a. prophase Ib. metaphase Ic. anaphase Id. telophase I
Meiosis• The form of cell division by which gametes (sperm or egg cells), with
half the number of chromosomes, are produced.
• Diploid (2n) haploid (n) n=# of chromosomes
• Meiosis is sexual reproduction.
• Two divisions (meiosis I and meiosis II).
Meiosis• Sex cells divide to produce gametes (sperm or egg).
• Gametes have half the # of chromosomes.
• Occurs only in gonads (testes or ovaries).
Male: spermatogenesisFemale: oogenesis
• Meiosis is similar to mitosis with some chromosomal differences.
Sex ChromosomesThe Sex Chromosomes code for the sex of the offspring.** If the offspring has two “X” chromosomes it will be a female. ** If the offspring has one “X” chromosome and one “Y” chromosome it will be a male.
XX chromosome - female XY chromosome - male
In Humans the “Sex
Chromosomes” are the 23rd set
Boy or Girl? The Y Chromosome “Decides”
X chromosomeY chromosome
Interphase I
• Similar to mitosis interphase.
• Chromosomes replicate (S phase).
• Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.
• Centriole pairs also replicate.
Interphase I•Nucleus and nucleolus visible.
nuclear membrane
nucleolus
cell membrane
chromatin
Prophase I• Longest and most complex phase (90%).
• Chromosomes condense.
• Synapsis occurs: homologous chromosomes come together to form a tetrad.
• Tetrad is two chromosomes or four chromatids (sister and nonsister chromatids).
Prophase I - Synapsis
Homologous chromosomes
sister chromatids sister chromatidsTetrad
Prophase I
centriolesspindle fiber
asterfibers
Crossing Over
•Crossing over (variation) may occur between nonsister chromatids
•Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.
Crossing Over - variation
nonsister chromatids
chiasmata: site of crossing over
variation
Tetrad
Another Way Meiosis Makes Lots of Different Sex Cells – Crossing-Over
Crossing-over multiplies the already huge number of different gamete types produced by independent
assortment.
Metaphase I• Shortest phase
• Tetrads align on the metaphase plate.
• INDEPENDENT ASSORTMENT OCCURS:1. The random separation of the homologous chromosomes---this results in GENETIC VARIATION
Homologous Chromosomes
• Pair of chromosomes (maternal and paternal) that are similar in shape and size.
• Homologous pairs (tetrads) carry genes controlling the same inherited traits.
• Each locus (position of a gene) is in the same position on homologues.
• Humans have 23 pairs of homologous chromosomes.
a. 22 pairs of autosomesb. 01 pair of sex chromosomes
Homologous Chromosomes
Paternal Maternal
eye color locus
eye color locus
hair color locus
hair color locus
Metaphase I
metaphase plate
OR
metaphase plate
Anaphase I• Homologous chromosomes separate and move towards the poles.
• Sister chromatids remain attached at their centromeres.
Anaphase I
Telophase I
• Each pole now has haploid set of chromosomes.
• Cytokinesis occurs and two haploid daughter cells are formed.
Telophase I
Meiosis II• No interphase II
(or very short - no more DNA replication)
• Remember: Meiosis II is similar to mitosis
Prophase II• same as prophase in mitosis
Metaphase II• same as metaphase in mitosis
metaphase platemetaphase plate
Anaphase II• same as anaphase in mitosis• sister chromatids separate
Telophase II
• Same as telophase in mitosis.
• Nuclei form.
• Cytokinesis occurs.
• Remember: four haploid daughter cells produced.
gametes = sperm or egg
Telophase II
Meiosis
2n=4
sex cell
diploid (2n)
n=2
n=2
meiosis I
n=2
n=2
n=2
n=2
sperm
haploid (n)
meiosis II
Meiosis – mouseParent cell
4 gametes
1st division
2nd division
Meiosis I
Draw This!
Meiosis II
Meiosis
Cells Dividing Clip
Crash Course Meiosis
Meiosis Pipe Cleaner Lab
Snowball Fight!