1)
Mitosis
 occurs in all body cells (somatic cells) in animals, plants, and humans
 production of 2 identical daughter cells that are diploid
 growth or replacement of body cells.
 asexual reproduction. (offspring and parents are identical)

2) Meiosis
 occurs only is sex cells (sperm and egg)
 production of the 4 non-identical gametes (sex cells) that are haploid
 Sperm and eggs have half the genetic information
 sexual reproduction

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10% time dividing (mitotic phase/meiotic phase)
90% time interphase (G1, S, G2 phases)

Interphase
1) G1 (gap phase) -manufactures proteins and amino acids needed for both cell processes and cell division, carries out metabolic duties
 Cell grows
2) S phase (synthesis phase) – DNA replicates .
-longest stage of the cell cycle

3) G2 (gap phase)
 increases the rate of protein synthesis and prepares to divide.
 grows larger

Division
 Mitosis or Meiosis
 cell can divide only about 50 times on average.
 To ensure that the cells in a tissue are healthy, cells will undergo a form of cell suicide called apoptosis .
 Cell Death

 Chromatin – complex long threads made of DNA and protein that makes up chromosomes
 Uncondensed chromosome – long, thin strands not visible with light microscope
 Condensed chromosome – short and visible

Chromosome vs. Chromatid
 Chromosomes replicate before division to form 2 matched sister chromatids

 Humans have 46 chromosomes (diploid or
2N)
 Sex gametes have 23 chromosomes (haploid or N
 Some organisms have polyploidy
 Ex) corn – 4n (tetraploidy)

– same size and shape and carry the genes for the same traits, but have different details
 Humans have 23 homologous chromosomes for a total of 46

Gene
 basic unit of heredity
 sequence of nucleotide bases in DNA.
 codes for a specific proteins

 Autosomes – chromosomes that do not influence gender (humans have 22 pairs of these)
 Sex Chromosomes – X and Y chromosomes that determine gender in humans (humans have 1 pair of these, the
23 rd chromosome pair)

 Early: chromatin condenses to form chromosomes, centrioles move to poles and attach to spindle fibres
 Late: spindle fibres attach to centromere, nuclear membrane dissolves

 chromosomes line up on the equatorial plate (center of the nucleus)

 Spindle fibres contract from the centrioles and sister chromatids begin to separate apart, immediately chromosomes being to unravel

 nucleolus re-appears, nuclear membrane reforms, the chromosomes unravel to form a loose mass of chromatin
 cells undergo cytokinesis (divide cytoplasm)

 a cell plate forms between the new daughter cells
 the cell membrane pinches in between the two daughter cells

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Mitosis Overall http://www.loci.wisc.edu/outreach/bioclips/CDBio.html

Some Methods of Asexual Reproduction
1. Binary fission - equal division of both the organism cytoplasm and nucleus to form two identical organisms ex: Protist, amoeba

2) Budding - one parent dividing its nucleus
(genetic material) equally, but cytoplasm unequally ex: Fungi- yeast

Occurs in sexual reproduction
The end result is 4 gamates that are genetically different
Spermatagonium 
4 sperms
Oogonium  4 eggs

Prophase I – homologous chromosomes undergo synapsis (pair up) and crossing over occurs .
-also, as in mitosis prophase:
Chromos condense
Nuclear membrane disappears
Centrioles move to opposite poles
-tetrad

 Metaphase I – homologous pairs line up along the equatorial plate, spindles insert into the centromeres.

 Anaphase I – homologous chromosomes separate and are pulled to opposite poles
= segregation

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Chromosomes undergo independent assortment in during Anaphase I
-increases genetic diversity

 Telophase I – daughter cells separate, each has one chromosome from each homologous pair.
-reduction has occurred so that the new cells will be haploid (n)
 -cytokinesis occurs

 Prophase II –spindles form

 Metaphase II –chromosomes align at the equatorial plate

 Anaphase II – the daughter chromatids separate and move towards separate poles

 Telophase II – spindle fibres disappear, nuclei reform and cytokinesis takes place.
(All 4 daughter cells are haploid.)

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The number of possible chromosome combination in a gamate is 2^n
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Where ‘n’ is the haploid number
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Ex. Humans n=23, thus 2^23 =8, 388, 608 different combinations!!
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Now THAT’S diversity!!

 NOVA Online | 18 Ways to Make a Baby |
How Cells Divide: Mitosis vs. Meiosis
(Flash)

Oogenesis

Spermatogenesis

 Oogenesis (female)
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 meiosis II completes only if egg is fertilized
Secondary oocyte receives most of the cytoplasm and becomes the egg polar bodies have less cytoplasm and degenerate one egg cell is produced
 Spermatogenesis
(male)
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 meiosis I and II are both completed before fertilization each sperm cell produced receives an equal share of cytoplasm
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 flagellum forms from one of the centrioles four spermatids are produced

 Female is XX
 Male is XY
XX XY

 Chromosomal abnormalities can be detected by doing a karyotype chart .
 Fetal cells are collected through amniocentesis or chorionic villi sampling

1. accurate replication of the chromosomes
2. exact separation / distribution of the chromosomes

 Trisomy –three chromosomes replace a normal pair (47 chromosomes in humans)

 Non-disjunction – occurs during meiosis when two homologous chromosomes move to the same pole.
Chromosomes do not separate properly
Normal Division Non-disjunction

Down’s syndrome – trisomy 21
 Extra 21 chromosome
 more common in children born to women over 40
 characterized by short stature, folds to the eyelids, stubby fingers, wide gap between
1st and 3rd toes, large fissured tongue, round head, palm creases, mild to severe mental retardation .

Edward’s syndrome – trisomy 18
 results in severe overall defects with a life expectance of only 10 weeks
Patau’s syndrome – trisomy 13
 results in non-functioning eyes, severe deficits and limited life expectancy.

Klinefelter’s syndrome – XXY male
 sterile males with underdeveloped testes, overdeveloped breast tissue and sub-normal intelligence

Metafemale – XXX female
 no obvious deficits however menstrual irregularities and early menopause are common, some have increase aggression
XYY male
 taller than normal, recurrent acne

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Turner’s syndrome – XO female
 females with short stature, broad chest, heart defects, lack of breasts and absence of sexual maturation and menstruation
Cri du Chat syndrome
 deletion of a portion of one copy of chromosome number 5, malformed face and head, short life

Cloning
 identical offspring are formed from a single cell or tissue of the parent. (similar to mitosis)
 when plants send out runners, when bacteria divide and in identical twins.

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How to Clone: (the quick and easy, yet not so successful way)
Take an egg cell from an adult female and remove the nucleus (enucleation).
 Replace the nucleus with the nucleus from a body cell of the individual to be cloned.
(the cell must be toti-potent, or have its identity genes turned off) (you can use stem cells here)

 Zap it!!! (a little magic is required here)
 Implant the zygote or blastula into the mother’s uterus.
 Wait until the gestational period is up and voila!
 Click and Clone

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1997-2003 nucleus from udder cell put into egg cell

 some think it is wrong!!! (ethical issue)
 artificially cloned organisms seem to age faster
 it is very time and resource consuming and is not guaranteed to work

 the ends of the chromosomes, called telomeres , shorten each time a cell divides, and when they become critically short, the cell dies.
Totipotent: when cells reach a certain number of divisions, or age,
DNA begins to altered

 abnormal, uncontrolled cell division.
 May be caused due to mutation of genes
 Tumour suppressor genes – suppress cell division. (mutation turns these off)
 Proto-oncogenes – stimulate cell division.
(mutation turns these on)
 Telomeres do not shrink in cancerous cells

 Cancer cells do not participate in helping the body to function.
 Cancer cells require and take away nutrients
 Cancer cells can break away
( metastasis ) from the tumour mass and spread to other parts of the body.
 NOVA Online | Cancer Warrior | How Cancer Grows