Chapter 6 Chromosomes and Cell Reproduction

Cell division (cell reproduction) Section 6-1 Cell division (cell reproduction) Occurs in humans and LT at diff times in their life Formation of gametes (egg/sperm) involves special types of cell ÷ (this will be covered in chapter 7) When cells ÷, DNA is 1st copied and then ÷

Prokaryotic (Bacteria) Cell Reproduction: Binary fission: Section 6-1 Prokaryotic (Bacteria) Cell Reproduction: Binary fission: Form of asexual reproduction in bacteria cells that produces identical offspring Binary fission occurs in 2 stages: 1st, DNA is copied, then cell ÷, eventually the ÷ prokaryote is pinched into 2 independent cells

Eukaryotic Cell Reproduction: Section 6-1 Eukaryotic Cell Reproduction: Gene: piece of DNA that codes for a protein or RNA As eukaryotic cell prepares to ÷, DNA and proteins associated w/ DNA coil into chromosomes Chromatids: 2 exact copies of DNA that make up each chromo Centromere: where 2 chromatids of chromo are attached

Homologous chromosomes: chromo similar in size, shape, genetic content Section 6-1 Homologous chromosomes: chromo similar in size, shape, genetic content Each homologue in a pair of homologous chromosomes comes from 1 of the 2 parents 46 chromosomes in human somatic (body) cells are actually two sets of 23 chromosomes (23 from mom, 23 from dad) Diploid: cell w/ 46 chromo (23 from mom, 23 from dad) Haploid: cell w/ only 23 chromo, such as gametes Zygote: fusion of 2 haploid gametes (fertilization) to form 1 diploid fertilized egg cell (mom’s 23 w/ dad’s 23 = 46)

Section 6-1 Autosomes: chromo not directly involved in determining sex (gender) of an individual; pairs #1-22 Sex chromosomes: 1 pair of chromo in humans, contain genes that determine sex of individual; pair #23 referred to X and Y; XX = female, XY = male

Humans missing 1 of 46 chromosomes usually don’t survive Section 6-1 Change in Chromo #: Humans missing 1 of 46 chromosomes usually don’t survive Trisomy: more than 2 copies of a chromosome, will not develop properly; 3 copies of #21= Down’s Syndrome Karyotype: photo of chromo in a dividing cell showing chromo arranged by size

Change in Chromo Structure: Section 6-1 Change in Chromo Structure: ∆ in organism’s chromo structure are mutations Breakage of chromo can lead to 4 types of mutations: 1. deletion mutation: piece missing 2. duplication mutation: piece added 3. inversion mutation: piece turned upside down 4. translocation mutation: piece from chromo is put on a different chromo

Repeating sequence of cellular growth/÷ during life of organism Section 6-2 Cell Cycle: Repeating sequence of cellular growth/÷ during life of organism Interphase: 1st 3 phases of cell cycle, 90% of cell’s time is in this phase

2. Synthesis (S) phase: DNA is copied Section 6-2 5 Phases of Cell Cycle: 1. 1st growth (G1) phase: cell grows rapidly and carries out routine functions 2. Synthesis (S) phase: DNA is copied 3. 2nd growth (G2) phase: preparations made for nucleus to ÷ 4. Mitosis: nucleus of cell ÷ into 2 nuclei 5. Cytokinesis: cytoplasm ÷

1. Cell growth (G1) checkpoint makes decision of whether cell will ÷ Section 6-2 Control of Cell Cycle: Checkpoints at which feedback signals from cell can trigger or delay next phase of cell cycle 1. Cell growth (G1) checkpoint makes decision of whether cell will ÷ 2. DNA synthesis (G2) checkpoint DNA replication is checked by DNA repair enzymes 3. Mitosis checkpoint triggers exit from mitosis

When Control Is Lost: Cancer! Section 6-2 When Control Is Lost: Cancer! If a gene that controls cell growth/÷ is mutated, then regulation of cell growth/÷ can be disrupted = cancer and uncontrolled cell growth results! Bladder cancer

Mitosis - Division of the Nucleus in 4 phases: Section 6-3 Mitosis - Division of the Nucleus in 4 phases: 1. Prophase: Nuclear envelope dissolves; spindle forms 2. Metaphase: Chromo move to center and line up along the equator 3. Anaphase: Centromeres ÷; chromo move to opposite ends of cell 4. Telophase: Nuclear envelope forms around chromo at each pole; Mitosis is complete

Cytokinesis – Division of the Cytoplasm: Section 6-3 Cytokinesis – Division of the Cytoplasm: As mitosis ends, cytokinesis begins Cytoplasm of cell ÷ in 1/2, cell membrane grows to enclose each new cell, forming 2 separate genetically identical cells from 1 cell