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Transcript
Cell Reproduction Notes Day 1 Warm Up Where are your genes located? http://people.na.infn.it/~nicodem/research/cell_genes.jpg •DURING MOST OF THE CELL’S LIFE, DNA FORMS A TANGLED MASS CALLED CHROMATIN. •CHROMATIN LOOKS LIKE A PLATE OF SPAGHETTI. •RIGHT BEFORE A CELL DIVIDES, THE CHROMATIN FORMS INTO CHROMOSOMES (XSHAPED). CHROMATIN MOST OF THE TIME CHROMOSOMES ONCE IN A WHILE Cell Division • • • • Chromosomes = Tightly coiled, rod-shaped DNA Chromosomes are made of chromatin Human body produces 2 trillion cells per day & 25 million per second Cells are formed by cell division of older cells 1. When a cell divides, DNA is first copied & then distributed 2. Each cell ends up with a complete set of DNA Chromosome Number • Each human somatic cell has 2 copies of 23 different chromosomes – Total 46 – Somatic = any cell that is NOT a sex cell – (also called body cells or autosomes) Sets of Chromosomes • Each pair is made up of 2 homologous chromosomes – Homologous chromosomes = chromosomes that are similar in size, shape, & genetic content – Each homologue comes from one of the parents • One from mom • One from dad Cells Can Be Diploid or Haploid • Diploid = a cell that contains 2 sets of chromosomes (2n) • Haploid (monoploid) = a cell that contains only 1 set of chromosomes (1n or n) Chromosomes Determine Your Gender • Humans have 23 pairs of chromosomes • 22 pairs are autosomes (chromosomes NOT directly involved in determining sex) • 1 pair are sex chromosomes (contain genes that WILL determine the sex) – X & Y chromosomes X & Y Chromosomes • Male = XY • Female = XX • Male (dad) can donate an X or a Y to offspring • Female (mom) can ONLY donate an X So-Which parent determines the sex of the baby? MALE XY Gametes • Gametes are reproductive cells – Males = sperm (n = 23) – Female = egg (n = 23) • Combine in fertilization to make a: – Zygote (n = 46) Karyotype • Karyotype = a photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size. Karyotype cont’d • Each of an individual’s 46 chromosomes has thousands of genes so the presence of all chromosomes is essential for normal functioning – Humans who are missing a chromosome don’t survive – Humans with more than two copies of a chromosome, called trisomy, may survive but will not develop properly. What is wrong? The Cell Cycle • Repeating sequence of cell growth and division during an organism’s life • 90% of cell life is spent in INTERPHASE • Then it may go into MITOSIS & CYTOKINESIS INTERPHASE (divided into mini-phases) • G1(first growth) phase = Cell grows rapidly • S (synthesis) phase = DNA copied • G2 (2nd growth) phase = Nucleus prepares to divide http://publications.nigms.nih.gov/insidethecell/ch4_interphase_big.html AFTER INTERPHASE • Mitosis • Cytokinesis • http://www.cellsalive.com/cell_cycle.htm Mitosis and Meiosis WARM UP Females are X___ Males are X___ Having 3 copies of a chromosome is called a ______________ Mitosis and Meiosis • Mitosis: -division of somatic (body) cells - results in two daughter cells that are identical • Meiosis -division of gametes (sex cells) Mitosis • Interphase • Prophase • Metaphase • Anaphase • Telophase The Cell Cycle is Carefully Controlled • Key check points which feedback signals from the cell will delay the next step • Controlled by proteins! 1. Cell Growth CHECKPOINT (G1) – Start – Nerve/muscle cells stop here 2. DNA Synthesis CHECKPOINT (G2) – Enzymes 3. Mitosis CHECKPOINT – Back to G1 phase When Control is Lost -- Cancer • Cancer = Cell growth is uncontrolled - does not respond to control mechanisms. • Causes: Mutations that cause over-production of growth molecules – (accelerator) or by inactivating proteins that slow or stop the cell cycle (brakes) • Tobacco and UV radiation linked to increased cancer risk. Change in Chromosome Number • Trisomy = humans with more than 2 copies of chromosomes – improper development • Karyotype = a photo of the chromosomes in a dividing cell. • Disjunction = when egg/sperm cells form – each chromosome and homologue separate – sometimes one or more chromosomes fail to separate - unequal distribution. • Down Syndrome - 3 copies of chromosome 21NONDISJUNCTION Change in Chromosome Structure • Mutation – A change in an organism’s chromosomal structure. • Deletion = piece of chromosome breaks off completely – lacks of a set of genes – fatal • Duplication = chromosome fragment attaches to its homologous chromosome –two copies of a gene set • Inversion = chromosome piece reattaches to original chromosome, but in reverse orientation. • Translocation = chromosome piece reattaches to a nonhomologous chromosome. Interphase • Interesting things happen! 1. Cell preparing to divide 2. Genetic material doubles Prophase • Chromosome pair up! 1. Chromosomes thicken and shorten -become visible -2 chromatids joined by a centromere 2. Centrioles move to the opposite sides of the nucleus 3. Nucleolus disappears Metaphase • Chromosomes meet in the middle! 1. Chromosomes arrange at equator of cell 2. Become attached to spindle fibres by centromeres 3. Homologous chromosomes do not associate Anaphase • Chromosomes get pulled apart 1. Spindle fibres contract pulling chromatids to the opposite poles of the cell Telophase • 1. 2. 3. Now there are almost two! Chromosomes uncoil Spindle fibres disintegrate Centrioles replicate Cytokinesis • Cell splits http://www.cellsalive.com/mitosis.h tm Metaphase Telophase Prophase Anaphase