The Ability to Divide and Reproduce Is a Characteristic of Living Organisms

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)

Plants : cell plate formation vesicle fusion at the metaphase plate

Animals: cleavage furrow formation of a contractile ring

You are expected to know the characteristists 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 occurs in Germ Cell (diploid) à Gametes (Sperm and Egg Cell (haploid)

Oogonia: diploid cells (germ) destined to become egg

Spermatogonia: diploid cells (germ) destined to become sperm

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). Diploidàhaploid

Meiosis II: separation of sister chromatid Production of 4 daughter cells (haploid)

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