CHAPTER 6 CHROMOSOMES & CELL REPRODUCTION Section 1 – Chromosomes Section 2 – The Cell Cycle Section 3 – Mitosis & Cytokinesis

Millions of cells are being reproduced every second Gametes – an organism’s reproductive cells (sperm or egg) Every cell contains DNA and this DNA must be replicated before the cell can divide Purposes for cell division: cell growth, cell repair and cell development FORMATION OF NEW CELLS BY CELL DIVISION

DNA is circular and attached to inner cell membrane Type of reproduction: Binary Fission – Asexual reproduction that produces offspring that are identical to the parent – Two stages DNA is replicated Parent cell is split down the middle PROKARYOTIC CELL REPRODUCTION

Genetic Material – Gene: subunit of DNA or RNA – Chromosome: DNA and proteins – Chromatid: two exact copies of DNA that form a chromosome During division, the chromatid is split at the centromere. EUKARYOTIC CELL REPRODUCTION

Humans have 23 pairs of chromosomes Homologous chromosomes: similar in size, shape and genetic material Diploid: somatic (body) cell has two sets of chromosomes Haploid: gamete cell has one set of chromosomes Zygote: a fertilized egg – when sperm and egg join SETS OF CHROMOSOMES

Autosomes(22 pairs): chromosomes that are directly involved in determining the sex (gender) of the individual Sex Chromosomes: contains genes that are involved in sex determination Human Sex Chromosomes: X and Y genes – Male: XY – Female: XX SEX CHROMOSOMES

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Trisomy: organism has more than two copies of a chromosome Karyotype: a photo that can be analyzed to find any abnormalities of chromosomes Down Syndrome: an extra copy of Chromosome 21 causing a short stature and round face – The risk for down syndrome is higher when a mother is 37 or older CHANGE IN CHROMOSOME NUMBER

A repeating sequence of cell growth and division during an organism’s lifetime Interphase: collection of the first three phases where a cell spends 90% of its life THE CELL CYCLE Cell Cycle Overview Video

Routine cellular functions and rapid growth Most cells stay in this stage the longest or stay in this stage if they never divide – Muscle and nerve cells never divide If a cell never leaves this stage they will eventually die and not be replaced Centrosomes are replicated as preparation for DNA replication THE CELL CYCLE FIRST GROWTH (G1 PHASE)

Beginning of DNA replication – chromosomes are replicated The cell must grow as the number of proteins increases during DNA synthesis The number of chromosomes is doubled and signifies the cell is ready for the G2 phase THE CELL CYCLE SYNTHESIS (S PHASE)

The nucleus must divide for two cells to form and during this phase the nucleus is prepared for that future situation Microtubules are arranged in positions that will used during mitosis The checkpoint that is involved here will check DNA for proper duplication THE CELL CYCLE SECOND GROWTH (G2 PHASE)

Process by which the cell’s nucleus is divided into two nuclei Each nuclei will have the same amount and type of genetic material This process contains four stages: Prophase, Metaphase, Anaphase & Telophase THE CELL CYCLE MITOSIS

Allows cells to produce asexually when needed These times include cell growth, cell repair (tissue repair) and cell development After cytokinesis, a cell will proceed to interphase to begin the process again! THE CELL CYCLE CYTOKINESIS

Cell Growth (G1) Checkpoint – Pass: large and healthy – Denied: too small – pushed back to rest DNA Synthesis (G2) Checkpoint – Passed: Repair enzymes have fixed issues – Denied: DNA not abled to be used Mitosis Checkpoint – Passed: DNA replicated – Denied: DNA not prepared CONTROL OF THE CELL CYCLE

Spindles: centrioles and microtubules that physically separate chromatids Spindles attach at centromere of the chromatids to separate the chromatids evenly Chromatids are pulled to opposite poles of the cell After chromatids are separated they are called chromosomes CHROMATID SEPARATION IN MITOSIS

Chromosomes coil up, nuclear envelope dissolves and spindle fibers form MITOSIS - PROPHASE

Chromosomes are lined up in the center of the cell (“equator”) and the spindle fibers attach to each side of the chromatids MITOSIS - METAPHASE

Chromatids are separated to opposite poles and called chromosomes. Spindle fibers now shorten. MITOSIS - ANAPHASE

At each pole the chromosomes are surrounded by a nuclear envelope MITOSIS - TELOPHASE

The cleavage furrow pinches and the one cell becomes two identical cells CYTOKINESIS

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