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Transcript
GENETIC VARIATION & CELL DEATH FUN FACT Mitosis usually occurs within 1-2 hours MALE (testis) Meiosis takes 1 month (Prophase1 = 1 week) FEMALE (ovaries) Meiosis takes decades (Prophase1 = before female is born) GENETIC MIXING *Only in Meiosis 1. CROSSING OVER During Synapsis (during Prophase1 to Metaphase1) 4 chromosomes form a tetrad Genetic material is exchanged by “non-sister” chromatid on homologous chromosomes 2. INDEPENDENT ASSORTMENT It is random how the homologs split up in Anaphase1 Can be different at every Meiosis More chromosomes = greater genetic variety Ex. Humans (23 chromosomes) 223 = 8,388,608 different combinations of maternal and paternal DNA 3. MUTATIONS A. Nondisjunction Homologous chromosomes don’t separate (disjoin) during Anaphase1 or pairs don’t separate in Anaphase2 Aneuploidy- organism with extra or missing chromosome 10-30% zygotes show aneuploidy, but most don’t develop into fetus Chromosome #21 Trisomy = Down Syndrome HUMAN NONDISJUNCTION CAUSING ANEUPLOIDY Ex. Homologs of Chromosme#21 don’t separate MEIOSIS: oogenesis #21 #21 No #21 #21 #21 24 chromosomes (1 extra) No #21 Fertilization 22 chromosomes (1 less) Down Syndrome #21 #21 #21 Egg Sperm #21 #21 #21 Zygote has Trisomy of Chromosome #21 OR MEIOSIS: oogenesis #21 #21 #21 #21 24 chromosomes (1 extra) No #21 No #21 22 chromosomes (1 less) Fertilization No #21 #21 Egg Sperm #21 Zygote has Monosomy of Chromosome #21 B. Polyploidy: many chromosome sets Most living are diploid (2n, animals) or haploid (1n, fungi) Sometimes Triploid (3n) or Tetraploid (4n) occurs Caused by extra round of DNA replication or if spindle doesn’t form *Can create new species Triploid can’t do meiosis, but even sets, like Tetraploid can do meiosis C. Translocation- Crossing Over occurs with NON-homologous pairs Common Loci (gene location) is important so Translocation can greatly change genetics Ex. Translocation of Chromosome #9 (gene abl) & #22 (gene bcr) = form of Leukemia, white blood cell cancer END OF CELL CYCLE: CELL DEATH PROGRAMMED CELL DEATH 1. Necrosis- cells are damaged mechanically, by toxins, or lack of oxygen/nutrients Swell and burst Release their contents into extracellular space Causes inflammation Ex. Diabetes or Frostbite Tissue Necrosis *if you get grossed out easily, do not look* 2. Apoptosis- planned cell suicide Because cell type is no longer needed (webbed connective tissue between human fetal fingers) 2. Cell is old (prone to genetic problems like cancer) 1. Cell detaches from neighbors & hydrolyzes DNA into small “blebs” Cell remains are digested by other cells’ phagocytosis (by lysosomes) Controlled by Signal Transduction pathways Activates Caspase (enzymes) hydrolyzes cell TUMOR PROTEINS 1. ONCOGENE Positive Regulator- makes cell division Proteins that became mutated or overactive Cause cancer cells to divide more Ex. “HER2” (Growth cancer receptor in Breast Cancer Cells) Excess HER2 in 25% of Breast Cancer tumors 2. TUMOR SUPRESSORS Negative Regulator- stops cell division Inactive in Cancer cells Ex. Retinoblastoma (RB protein)- stops G1 from continuing into cell cycle. HPV (human papoloma virus) makes protein E7 E7 fits perfectly into RB protein and inactivates it from working Causes Cervical Cancer