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Transcript
Cell Division, Part I: Mitosis What is function of mitosis?. Summary of mitosis 1. exact replication of ___________________ 2. replicated chromosome: 3. Cell splits. This is called ______________. The Chromosome What is a chromosome? What is function of proteins in the chromosome? How many chromosomes are contained in a human cell?) A primary task during cell division is replication of the chromosomes 1 Mitosis & Cytokinesis are part of the cell cycle G1 – S– G2 – M– Replication of the Chromosomes During stage of Interphase The two DNA strands separate & each acts as a "template" What is a template? Replicates remain attached for a while - what are these replicated chromosomes called? 2 Four Stages of Mitosis 1. Prophase Chromatin condenses into: ________________________________ ________________________________________________________ Nucleolus and nuclear membrane ___________________________ _________________________________________________________ spindle microtubules ______________________________________ 2. Metaphase Chromosomes line up _____________________________________ ______________________________________________________ ______________________________________________________ 3. Anaphase – _______________________________________________ fibers toward the ends of the cell (opposite poles). The __________ _________ are separated from each other, they are now considered to be _______________ 4. Telophase – ____________have reached opposite ends of the cell. The ______________ disassemble. Chromosomes return to less coiled ________ state. __________ ________ begins to form around the chromosomes at the end of each cell. ____________ begins. Cytokinesis - Completes __________. Cytoplasm of a cell and its organelles separate into 2 new daughter cells. Animal cells: __________divides when cleavage furrow deepens until the parent cell pinches into _____________ which are now in Interphase. How does cytokinesis differ in plants? Material for new cell wall called __________ gather & fuse along middle (______) of cell, between 2 nucleus forming ___________________. 3 Muscle cells: mitosis without cytokinesis Once formed, muscle cells can increase in _________________. Become ____________. A cell that has many nuclei is called a __________ (pronounced “sin-SISH- ium”). Why multiple nuclei in each cell? Each skeletal muscle cell is made up of many precursor cells, called ________, which have fused together to form one long, thin cell with many nuclei. The muscle cells need these multi-nuclei to multi-task. i.e.: _____________________. Control of the Cell Cycle Different cell types divide at different rates Rapid dividers skin intestinal lining hair follicles Slow dividers muscle cells neurons liver cells When good cells go bad: CANCER = Mitosis out of control Results from ___________ (usually several) in a single cell E.g. genes involved in regulating growth or suppressing tumors Tumor = ______________ of tissue What is a Malignant tumor? Cancer, _________________ that can invade other tissues Unusual properties of cancer cells Abnormal growth- ________ is uncontrolled as cell growth is not inhibited when the _____________________ with another cell Cells are undifferentiated 4 Example – Lung Cancer 160,000 deaths/year 80-90% caused by smoking Only 12-15% of patients cured ``A cigarette is a euphemism for a cleverly crafted product that delivers just the right amount of nicotine to keep its user addicted for life before killing the person.'' Gro Harlem Brundtland Director General, World Health Organization 5 Cell Division, Part II: Meiosis Special type of cell division to produce __ ________________ What is a gamete? _____________ So, where in the body does meiosis occur?________________ Meiosis produces daughter cells with half the normal chromosome number Somatic cells (non-gametes) have ____ chromosomes . . . . . . but there are only ____ “types” chromosomes of same type are said to be ____ _________________ Why do chromosomes come in homologous pairs? _______________ ____________________________________________________________ The 23 pairs of chromosomes can be divided into 22 _________________ and one pair of ___________________________ Meiosis is cell division that reduces chromosome number by half Gametes (23 chromosomes) are called ________________ Somatic cells (46 chromosomes) are called _________________ 6 Meiosis involves 2 cell divisions Meiosis I in first metaphase chromosomes line up in homologous pairs what does this picture represent? XX XX XX XX 7 Meiosis II ___________ separate just as in mitosis (but with _______ the number of chromosomes) X X Meiosis and Fertilization increase genetic variability in several ways 1. Crossing Over 2. Independent Assortment (Random Assortment of Homologues) 3. Fertilization 8 IGNORE # homologous pairs # combinations 22 24 25 223 2 4 5 23 = 4 = 16 = 32 = 8,388,608 Errors in Meiosis Non-disjunction: chromosomes don’t separate Trisomy 21 most common chromosome number abnormality Why? Meiosis and sex determination Non-disjunction of ______________ shed light on mechanism of ____________ Normal ♀ Normal ♂ XX XY Is sex determined by number of X’s or Y’s? XO XXY 9 10 HEREDITY Early Ideas Blending inheritance- Short-lived theory that the sperm and egg of parent organisms contained a sampling of the parent's "essence" and that they somehow blended together to form the pattern for the offspring. What is it? The theory of blending inheritance referred to an actual blending of the genetic material (i.e. in modern terms, alleles would blend together to form a completely new allele). Later replaced by the view of _____Mendelian_____ inheritance Inheritance of acquired characteristics What is it? This theory proposed that genetic traits of a parent are passed onto offspring on the basis of modification from use. One classical example is the giraffe neck; which was proposed to be passed on to F1 and F2 generations based on the parent's strain to higher trees. The first modern geneticist? ____Gregor Mendel________________________ 1866 - “Treatise on Plant Hybridization” Mendel’s Experiment: P1 Purple (PP) x P p P Pp Pp White (pp) P Pp Pp 11 Mendel concluded: To explain his results, Mendel formulated a hypothesis that included the following: 1. that the inheritance of each trait is determined by "units" or "factors" that are passed on to descendents unchanged (these units are now called genes ) 2. that an individual inherits one such unit from each parent for each trait (the principle of segregation) 3. that a trait may not show up in an individual but can still be passed on to the next generation. * According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. Which allele in a parent's pair of alleles is inherited is a matter of chance. We now know that this segregation of alleles occurs during the process of sex cell formation (i.e., meiosis ). * According to the principle of independent assortment, different pairs of alleles are passed to offspring independently of each other. The result is that new combinations of genes present in neither parent are possible. For example, a pea plant's inheritance of the ability to produce purple flowers instead of white ones does not make it more likely that it will also inherit the ability to produce yellow peas in contrast to green ones. Likewise, the principle of independent assortment explains why the human inheritance of a particular eye color does not increase or decrease the likelihood of having 6 fingers on each hand. Today, we know this is due to the fact that the genes for independently assorted traits are located on different chromosomes . * If an organism has two unlike factors (we call them alleles) for a characteristic, one may be expressed to the total exclusion of the other (dominant vs recessive). 12 Modern Terminology for Mendel’s discoveries Different forms of a gene are called __alleles_________ example: eye color: blue, brown flower color: purple, white The combination of alleles carried by an individual is her ____genotype_____ example: BB- homozygous dominant for brown eyes Bb- heterozygous for brown eyes What is the relationship between the two genes you have for a trait and the homologous chromosomes? The genes are carried on the homologous chromosomes. The appearance of an individual is her ___phenotype_____. Why did F2 generation have a 3:1 ratio? F1 Pp x Pp (note that both parents are heterozygous) meiosis The Punnett Square makes it easy to determine outcome of crosses P p P PP Pp p Pp pp 13 The Test Cross What is the genotype of the white-flowered plant? pp What is the genotype of the purple-flowered plant? Pp, PP Mendel also did crosses involving two traits this is called a ____dihybrid cross______ where: R = round (dominant) & r = wrinkled seeds (recessive) purple flower, round seeds x Punnet Square for dihybrid cross PPRR x pprr PR PR Pr pR Pr PPRR PPRr PpRR PpRr PR PPRR PPRr PpRR PpRr PR PPRR PPRr PpRR PpRr PR PPRR PPRr PpRR PpRr 14 white, wrinkled Phenotype General Genotype 9 Purple, Round Seed P_W_ 3 Purple, Wrinkled Seed P_ww 3 White, Round Seed ppW_ 1 White, Wrinkled Seed ppww Beyond simple Mendelian genetics 1. Linked Genes Genes assort independently only if they are on different chromosomes If the are on different chromosomes They can line up like this…. or they can line up like this Gametes but if the alleles are on the same chromosome, how many alleles can be produced? 15 Linked and Sex-Linked Genes So, what would a dihybrid cross look like if the genes for flower color and seed shape were on the same chromosome, i.e. if they were linked? purple flower, round seeds x white, wrinkled PPRR pprr Linked genes only produce 1 allele for each set of traits: If P is linked to R, only PR gametes are possible. If p is linked to r, only pr gametes are possible. PR PR pr PPRR PpRr pr PpRr pprr Instead of a 9:3:3:1 phenotypic ratio with independent assortment the ratio is 3:1. … unless crossing over occurs 2. Incomplete dominance = Intermediate inheritance where both heterozygous alleles are expressed e.g. snapdragon flower CC red x C’C’ with incomplete dominance, the red doesn’t completely express. The resulting color is pink. white 16 Is incomplete dominance the same thing as the “blending inheritance” as envisioned by 19th century biologists? No. I n the case of blending, there would be no chance of red or white showing in future generations. Incomplete dominance doesn’t alter the genotype of the plant, red or white can still be expressed. 3. Codominance = __both alleles are expressed: red flowers with white spots. e.g. ABO blood type 4. Polygenic inheritance = ____multiple gene inheritance______ e.g. skin color depends on melanin concentration Multiple Gene (Polygenic) Inheritance Assuming 2 alleles per gene (locus), # genes 1 2 3 n # genotypes 3 9 27 3n 17 5. Pleiotropy = a gene that affects more than one phenotype Albinism 6. white skin & hair hypersensitivity to light poor vision poor eye muscle control Sex-Linked genes = ____genes carried by either sex chromosome_______ X-linked recessive traits are always expressed in males red-green color blindness hemophilia 18