Cell Replication:
The ability to divide and reproduce is a characteristic of living organisms.
It allows for : Cell Replacement, Cell and Wound Repairs,
Growth
DNA replication must precede cell division. DNA houses all information for reproduction, development and
maintenance of the cell and the organism.
Genes provide information for the production of proteins that perform most of the cells work. Information for the
protein sequence is determined by the base sequence. The sum of all genetic information in an organism is included
in what we call the genome.
DNA is packaged in chromosomes.
Chromatin is long strands of DNA wrapped around proteins.
A chromosome is a packaged and condensed strand of Chromatin (DNA and Protein). When DNA is
replicated two identical copies are made of one chromosome.
Different organisms have different chromosome numbers; Haploid number.
Humans = 23
Onions = 8
Most eukaryotic cells are diploid: have pairs of the same chromosome; these pairs represent the homologous pairs
(these chromosomes are not identical, they carry the information for the same trait, but alternative forms).
Sex Chromosomes: humans and mammals use chromosomes to determine sex. Males have one X and one Y:
females have two Xs.
The egg contains 23 chromosomes (22 autosomal + 1 X)
The sperm contains 23 chromosomes (22 autosomal + 1 X or 1 Y)
Karyotype. Orderly display of magnified images of the individuals chromosomes. Cells are arrested at metaphase
and magnified.
Two type of Cell Division in most Eukaryotes: Mitosis (identical) and Meiosis (reductional ). Both are preceded by
interphase an intensely active phase where the cell prepares itself for mitosis or meiosis. During interphase DNA is
replicated.
Preparation for mitosis and meiosis and interphase are included in the Cell Cycle.
The Cell Cycle lasts 24 hrs. There are three phases
1. Interphase: includes G1, S (duplication of DNA 6of 23.5hrs) and G2 , lasts 23.5 hr
2. Mitosis or identity division (nuclear division). Begins with one diploid cell and produces of two
identical diploid daughter cells; sister chromatids condense, align themselves,and separate in 4
stages that lasts 30 minutes includes
 Prophase: (plain to see)
 Metaphase (middle)
 anaphase (apart)
 telophase (two nuclei)
3. Cytokinesis (div of the cytoplasm and plasma membrane to form two distinct cells)
Cytokinesis usually starts in late anaphase or early telophase
In Animals: cleavage furrow formation of a contractile ring.
In plants cytokinesis occurs by means of a phragmoplast. The phragmoplast forms the cellplate.
The phragmoplast is a cylinder consisting of microtubules that are derived from the spindle and
aligned between the daughter nuclei. The cell plate consistes of two new plasma membranes and
cell walls. It forms between the nuclei and in the center of the phragmoplast. It gradually extends
to divide the cell into two daughter cells.
MAKE CERTAIN YOU CAN RECOGNIZE CELLS IN EACH STAGE:
You are expected to know the characteristics of the nucleus and the chromosomes and spindle at each phase.
Cancer: uncontrolled cell division: Genes involved in Cancer
Oncogene: stuck accelerator
Tumor suppressor genes: failed brakes
Cyclin-dependent kinases: act in linked chain of protein activity
MEIOSIS : SEX CELL DIVISION REDUCES THE CHROMOSOME NUMBER BY HALF.
Meiosis occurs in Germ Cell (diploid)  Gametes (Sperm and Egg Cell (haploid)
Oogonia: diploid cells (germ) destined to become egg begins in the ovary
Spermatogonia: diploid cells (germ) destined to become sperm occurs in the testes.
Meiosis: begins with DNA replication (Interphase), has two nuclear divisions, followed by cytokinesis. Meiosis
begins with one diploid cell and produced 4 haploid cells.
Meiosis has 2 meiotic divisions following Interphase:
Meiosis I: Includes Prophase I, Metaphase I Anaphase I and Telophase I, no cytokinesis. Meiosis I accomplishes
the following: Crossing over, separation of homologous chromosomes (note tetrad). Diploidhaploid
Meiosis II: separation of sister chromatid Production of 4 daughter cells (haploid)
Compare Spermatogenesis with Oogenesis
Alterations is Chromosome Number and Structure due to non-dysjunction,
1. Trisomy 21: 3 copies of Chromosome 21 in the diploid cell
2. Klinefelters Syndrome : XXY sterile male with small testes and breast. A extra Y results in conversion of
female to male
3. Hypermale: XYY . Extra tall, otherwise normal
4. Metafemale: XXX reduced fertility otherwise normal
5. Turner’s Syndrome: XO shorter than average, unusual web of skin between neck and shoulder, reduced
fertility
Chromosomal alteration:
1. Deletions: fragment of chromosome removed
2. Duplication: one fragment moves to another chromosome giving 2 copies
3. Inversion: a fragment moves to another place oriented in the opposite direction
4. Translocation: attachment of a chromosome fragment to a non-homologous chromosome
Genetic Diversity: increases the chances of survival of a species. Is accomplished by
Mutations (a change in the nucleotide sequence of a gene)
Sexual Reproduction
Crossing Over
Independent Assortment of chromosomes
Life Cycle of Humans and Other Sexual Reproducing Organisms
Meiosis creates haploid gametes
Fertilization of gametes produces zygote (diploid cell)
Trillions of mitotic divisions produces Baby
Continued growth and cell death produces Adults
Meiosis creates haploid gametes
SUMMARY OF DIFFERENCES IN MEIOSIS, MITOSIS AND BINARY FISSION