Download Cell division notes complete

Cell division notes complete
Cell Division ­ Mitosis and Meiosis
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students will describe the processes of mitosis and meiosis define and explain the significance of chromosome number in somatic and sex cells
explain the events of the cell cycle
compare the formation of identical and fraternal twins
Chromosome Structure and Vocab
Haploid (n)
gametes (eggs and sperm)
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23 chromosomes in humans •
Diploid (2n)
Somatic cells (non gametes)
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46 chromosomes in humans
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Cell division notes complete
The Cell Cycle
Growth and division of somatic cell
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How multicellular organisms grow in size
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Two phases: Interphase and Division Phase
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Division Phase
Cell Cycle
Interphase
Interphase
Longest phase in the cell cycle •
Cell grows in size
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Doubles cytoplasmic organelles
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Duplicates chromosomes
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Three parts: G1, S, G2
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o G1: cell growth
o S: synthesis of DNA (chromosome duplication
o G2: cell growth and preparation for division
Division Phase
Mitosis and Cytokinesis
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Cell splits into two identical cells
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Cell division notes complete
Mitosis
4 stages: Prophase, Metaphase, Anaphase, Telophase
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Prophase
Chromosomes condense
Centrioles form and move to opposite ends of cell
Spindle fibers form and attach to centromeres
Nuclear membrane starts to dissolve
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Metaphase
Chromosomes (sister chromatids) move to center of cell (equatorial plate)
Nuclear membrane completely dissolved
Chromosomes most visible at this stage
Chromatids can become intertwined
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Anaphase
Centromeres divide
Sister chromatids (now separate chromosomes) move to opposite ends of cell
Should be identical chromosomes at each end
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Telophase
Chromosomes lengthen (expand)
Spindle fibers dissolve Nuclear membrane reforms around each group of chromosomes
Cytokinesis
Cytoplasm divides
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End with two identical cells •
o Both still 2n
Cell division notes complete
Mitosis and Aging (pg 562 and 570 in text)
Limited # of divisions
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Biological clock may regulate # of cell divisions allowed
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Study on heart cells
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Specialization affects mitosis rate
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o More specialized cells divide fewer times
Telomere (cap at end of chromosome) controls # of divisions
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o In normal cells: telomeres shorten every time the cell divides until it can’t shorten anymore without affecting the chromosome. Cell is at max age and dies
Telomere
Black bands represent genes
o In abnormal cells: cell keeps dividing and chromosome shortens = lose genetic information = abnormal cells
o In cancer cells: telomeres don’t shorten with each division, so cell never stops dividing
This is due to the presence of enzyme telomerase in cancer cells that prevents shortening of telomeres.
Cell division notes complete
Cloning
Forming identical offspring from a single cell or tissue in the parent organ
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Clone and parent have identical DNA
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Happens naturally in nature (pg 565)
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o Budding
o Runners
o Identical twins
Allows for production of strains of plants with predictable characteristics
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Animal Cloning (1960s +)
Frog cloning (pg 567)
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o Blastocyst nucleus inserted into enucleated (no nucleus) egg cell
o Egg cell divides mitotically to develop into normal embryo and then frog o New frog is genetically identical to original embryo o Nucleus from older cells (gastrulation stage) did not work as well ­ cells already too specialized to undergo mitosis
Mammal cloning
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o Same process as frogs
o Only seemed to work with nucleus from blastocyst cells
o Then Dolly happened
o Took nucleus from adult cells (udder cells) of Finn Dorsett and put in enucleated egg cell of Poll Dorsett
o New embryo (with transplanted nucleus) put into surrogate sheep’s womb (Scottish Blackface)
o Lamb was born that was genetically identical to first adult (Finn Dorsett)
Review questions
Pg 571: #1­4
Cell division notes complete
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students will describe the processes of mitosis and meiosis describe the process of meiosis and the necessity for the reduction of chromosome number
compare the processes of mitosis and meiosis
describe the processes of crossing over and nondisjunction
Meiosis
cell division to form sex cells (aka gametes, sperm, eggs)
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happens only in testes and ovaries
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gametes are haploid (n)
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goes through 2 divisions similar to Mitosis
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starts with G1, S, G2
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Meiosis I
homologous pairs separate
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Prophase I
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o Nuclear membrane dissolves
o Centrioles form and move to opposite ends
o Spindle fibers form and attach to centromeres
o Synapsis occurs: homologous pairs come together and intertwine o (tetrad = 4 chromatids)
o Crossing over may occur (pieces of chromatids break off and exchange) = variability in offspring
Synapsis
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Metaphase I
Tetrads line up on equatorial plate
** For simplicity, I will assume no crossing over happened for the next stages**
Anaphase I
Homologous chromosomes separate to opposite ends (segregation)
Chromosome number has now been reduced to n
**Which ones (red or blue) go left or right is completely random for each pair. **
Telophase I
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o Nuclear membrane forms around each set
o These two new cells are not identical (unlike in mitosis) because one has one set of the homologous pair and the other has another set.
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Cytokinesis
Cell membrane separates and you are left with two new haploid cells
Then both start Meiosis II without going through G1, S, G2
Cell division notes complete
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Meiosis II
Sister chromatids separate (like in mitosis)
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Prophase II
Nuclear membrane dissolves
Centrioles form and move to opposite ends
Spindle fibers form and attach to centromeres
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Metaphase II
Sister chromatids line up on equatorial plate
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Anaphase II
Sister chromatids separate to opposite ends Chromosomal number is still haploid
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Telophase II
Nuclear membrane forms around each set
These two new cells should be identical if there was no crossing over previously.
• Cytokinesis
o Cell membrane separates and you are left with four new haploid gametes
Cell division notes complete
students will describe the processes of mitosis and meiosis •
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describe the diversity of reproductive strategies by comparing the alternation of generations in a range of organisms
Key Terms
Sporophyte: structure that releases spores ­ Diploid
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Spores: grow into gametophyte
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Gametophyte: structure that makes gametes ­ Haploid
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Know the vocabulary and which ones are diploid or haploid. Don't have to know specific plants.
Cell division notes complete
Cell division notes complete
Cell division notes complete
Cell division notes complete
Abnormal Meiosis
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Nondisjunction
2 homologous chromosomes fail to separate during meiosis or mitosis
1 daughter cell has too many, 1 has too few chromosomes
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chromosomes
Too much or too little, don’t function properly
More consequences in meiosis = fetus that’s missing or has too many chromosomes
Polyploidy
More than 2n (nondisjunction of all chromosomes)
3n triploidy
4n tetraploidy
Failure of 2n zygote to divide after replicating (4n embryo)
Common and chemically encouraged in plants such as wheat, oats, tobacco, and potatoes
Humans and nondisjunction
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o Split at meiosis II produces gametes of 22 and 24 chromosomes (instead of normal 23, 23)
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Therefore after fertilization with a normal gamete, you get embryo of either 45 or 47
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1 chromosome where there should be 2 = monosomy
3 chromosomes where there should be 2 = trisomy
As individual develops, every cell will either be 1 short or have 1 too many
Disorders
Down Syndrome
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Turner Syndrome
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Klinefelter syndrome
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Trisomic female