Week 10 Notes
Week 10 Notes Bio 208
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This 8 page Class Notes was uploaded by Kylie McLaughlin on Tuesday November 3, 2015. The Class Notes belongs to Bio 208 at Northern Illinois University taught by Dr. Ed Draper in Fall 2015. Since its upload, it has received 9 views. For similar materials see Fundamentals of Cell Biology in Biological Sciences at Northern Illinois University.
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Date Created: 11/03/15
Week 10 Notes: Chapter 12 cont. the mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis MTs are dynamic: tubulin dinners can polymerize to form MTs where and when MTs form is controlled by MTOCs (MT organizing centers) MTs can depolymerize and release tubulin dimers, other MTs can form and do other jobs in the cell the spindle includes the centromeres, the spindle microtubules and the asters a centrosome is at each pole of the spindle (yellow “cloud”), it is an MTOC animal centrosomes contain a pair of centrioles (not found in plant chromosomes) the metaphase plate is at the equator; it is a place, not a structure 3 types of MTs emanate from the poles: 1. Kinetochore MTs are attached to kinetochores (protein structures attached to centromeres) 2. Nonkinetochore MTs from each pole overlap and interact with each other 3. Astral MTs project outward from the poles phases of mitosis in an animal cell (LOOK @ diagrams in BOOK) Late G2 of Interphase chromosomes are duplicated (occurred during S phase); there are 2 sister chromatids per chromosome NE is intact nucleoli are visible chromosomes are decondensed centrosomes (and centrioles in animal cells) are present and duplicated Prophase (P) (prepare for division) spindle MTs polymerize, which pushes poles (centrosomes) apart chromosomes condense nucleoli disappear Prometaphase (PM) (chromosome attachment to spindle MTs) NE breaks down some MTs attach to kinetochores → kinetochore MTs other MTs do not attach → nonkinetochore MTs chromosomes are pulled/pushed back and forth by kinetochore MTs until… Metaphase (M) (chromosome alignment) all kinetochores are equidistant between the 2 poles chromosomes are aligned on the metaphase plate Anaphase (A) (chromosome separation) sister chromatids separate → each is now an individual chromosome kinetochore MTs shorten (depolymerize); sets of chromosomes more toward opposite poles poles are pushed apart by nonkinetochore MTs result: one set of identical chromosomes is at each pole Telophase (T) (“end phase”) approx. reverse of prophase NE reforms spindle MTs depolymerize chromosomes decondense nucleoli reappear Cytokinesis (CK) division of the cytoplasm, which is achieved by: 1. Cleavage furrows in animal cells 2. Cell plates in plant cells the “+ ends” of MTs are attached to kinetochores, and the “ ends” are at the poles prometaphase: two types of motor proteins make chromosomes either way from or toward the poles dynein binds at positive end and moves towards negative end anaphase: 1. MTs depolymerize at the kinetochores + ends a. At the same time motor proteins pull chromosomes toward the poles 2. Nonkinetochore MTs (which overlap in the middle of the spindle) slide past each other and push the poles apart mitosis in plants: plant cell mitosis (onion root) is similar to that centrosomes (MTOCs at poles) lack centrioles centrosomes in plant cells don’t have centrioles animal cells: cleavage furrow, force is generated by actin and myosin (as in muscle) plant cells: phragmoplast, vesicles (transported by MTs) fuse to form a cell plate (new PM and cell wall) Chapter 13: Meiosis and Sexual Life Cycles living organisms are distinguished by their ability to reproduce their own kind heredity: is the transmission of traits from one generation to the next variation: is demonstrated by the differences in appearance that offspring show parents and siblings genetics: is the scientific study of heredity and variation Comparison of Asexual or Sexual Reproduction asexual reproduction: a single individual passes all of its genes to its offspring without the fusion of gametes a clone is a group of genetically identical individuals from the same parent in sexual reproduction: two parents give rise to offspring that have unique combinations of genes inherited from two parents Mitosis of the parent (2n) produces a multicellular organism composed of genetically identical cells these cells are a clone a group of cells can detach from the parent and become a complete individual the “bud” is a clone of the parent plants are also capable of reproducing asexually prepared from cells in metaphase, when chromosomes are most highly condensed identify chromosomes by: 1. Size 2. Banding patterns 3. Position of the centrosome a diploid cell has two almost identical chromosomes, which are called homologous or a homologous pair you have one homologue of each type from your mother and the other from your father human males and females have 22 pairs of autosomes and one pair of sex chromosomes female: XX male: XY cell in G2 has 6 chromosomes (there also would be 6 chromosomes during G1) Why Doesn’t the Number of Chromosomes Continually Increase in Sexually Reproducing Organisms? a gamete (sperm or egg) contains a single set of chromosomes and is haploid (n) for humans, the haploid number is 23 (n = 23) each set of 23 consists of 22 autosomes and a single sex chromosome Human Sexual Life Cycle meiosis reduces the diploid number by half: 2n → 1n each in cell gets one copy of each homologue the only 1n cells in humans are gametes: ovaries make eggs in unfertilized egg, the sex chromosome is: testes make sperm in a sperm cell the sex chromosome may be: fertilization restores the diploid number: egg (1n) + sperm (1n) → zygote (2n) zygote (2n) divides by mitosis to produce the body or soma (also 2n) The Variety of Sexual Life Cycles the alternation of meiosis and fertilization is common to all organisms that reproduce sexually the three main types of sexual life cycle differ in the timing of meiosis and fertilization sexual life cycles: mitotic cell division produces an organism’s multicellular body (soma) animals: 2n only body cells are 2n gametes are the only 1n cells plants: 1n and 2n body cells are 1n or 2n gametes are also 1n fungi and some potists: 1n only body cells are 1n zygotes are the only 2n cells begins with chromosomes consisting of duplicated sister chromatids (same as mitotic cells in G2) two divisions occur without an intervening S phase no S phase between meiosis I and meiosis II meiosis I: reductive division → only n (separate homologous chromosomes) meiosis II: similar to mitosis → pull apart sister chromatids,4 daughter haploid cells Phases of Meiosis in an Animal Cell Meiosis I: prophase I, metaphase I, anaphase I, telophase I and cytokinesis Meiosis II: prophase II, metaphase II, anaphase II, telophase II and cytokinesis MeiosisI: Reductive Division ProphaseI: like mitosis in that NE breaks down, MTs attach to the kinetochores chiasmata shows where cross over occurs between a sister chromatid MetaphaseII tetrads become aligned on the metaphase plate alignment is random with regard to which homologue faces which pole AnaphaseI homologues are separated from each other Telophase1, CytokinesisI daughter cells are haploid each chromosome consists of 2 sister chromatids MeiosisII: The Separation of Sister Chromatids (similar to mitosis) end up with 4 daughter cells (not genetically identical, haploid) sex is very expensive energy costs increased chance of predation injury during competition for mates a sexual life cycle produces new gene combinations some combinations will lead to greater fitness than that of the parents or others in the population genetic variation is the raw material for evolution sources of variation: 1. Independent assortment in meiosis I a. Of homologous in meiosis produces many types of gametes (egg + sperm) b. Number of types of gametes = 2^1n c. 1n = haploid number for species 2. Random fertilization a. Any egg (1n) could be fertilized by any sperm (1n) to produce a zygote (2n) b. Number of types of zygotes = 2^2n c. 2n = diploid number for species 3. Crossingover in prophase I a. During prophase I b. Crossing over produces recombinant chromosomes, which combine DNA inherited from each parent c. Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome in humans an average of one to three cross over events occurs per chromosome the locations of crossovers are random this generates much additional variation (but is hard to quantify it precisely) Chapter 14: Mendel and the Gene Idea Gregor Mendel, 18221884 agrarian upbringing studied math, chemistry and physics in Vienna mathematical descriptions of nature Augustinian monk in Brno. Teacher; later became abbot (monastery leader) pea breeding experiments, ca. 18551865. Published results in 1866, sent papers to the top European scientists and got no response his notes were burned after he died later discoveries: mitosis in 1875 and meiosis in 1890 results and laws rediscovered in 1900 (correns, tschermak, devries) mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments truebreeding: is an organism that always passes down certain phenotypic traits cross pollination: The transfer of pollen from an anther of a flower of one plant to a stigma of a flower of another plant of the same species hybridization: is the process of combining two complementary singlestranded DNA or RNA molecules and allowing them to form a single doublestranded molecule through base pairing seeds are the offspring, they grow into plants with the same genes as the seed in a typical experiment, mendel mated two contrasting true breeding varieties, a process called hybridization the true breeding parents are the P generation the hybrid offspring of the P generation are called the F1 generation when F1 individuals selfpollinate or cross pollinate with other F1 hybrids, that’s the F2 generation character: heritable traits, very from individual to individual trait: actual manifestation of that character all characteristics had 2 clearly different traits; purple/white flowers, green/yellow seeds, tall/short stems F1: only the dominant trait appeared F2: recessive trait reappeared and was ¼ or 25% of the total 3:1 ratio, dominant:recessive Mendels Model mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring four related concepts make up this model these concepts can be related to what we know about genes and chromosomes First: alternative versions of genes account for variations inherited characters for example, the gene for flower color in pea plants exits in two versions, one for purple flowers and the other for white flowers these alternative versions of a gene are called alleles each gene resides at a specific locus on a specific chromosome Second: for each character, an organism inherits two alleles, one from each parent mendel made this deduction without knowing about chromosomes the two alleles at a particular locus may be identical, as in the truebreeding plants of mendels P generation alternatively, the two alleles at a locus may differ as in the F1 hybrids Third: if the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance and the other (the recessive allele) has no noticeable effect on appearance in the flower color example, the F1 plants had purple flowers because the allele for that trait is dominant Fourth: (the law of segregation) the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes thus, an egg or sperm gets only one of the two alleles that are present in the organism this segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis Law of Segregation: Mendels 1 law AA x aa → Aa x Aa → ¼ AA , ½ Aa, ¼ aa genotypes 1:2:1 1/4 AA homozygous dominant 1/2 heterozygous 1/4 aa homozygous recessive two alleles are separated from each other at meiosis, recessive phenotype is masked in F1 but it reappears in F2 in F2, get 1:2:1 genotype ratio and 3:1 phenotype ratio The Law of Independent Assortment mendel identified his second law of inheritance by following two characters at the same time crossing two truebreeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters a dihybrid cross, a cross between F1 dihybrids can determine whether two characters are transmitted to offspring as a package (1) or independently (2) 1. Remain together (parental types only) 2. Assort independently (new types) using a dihybrid cross, mendel developed the law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation this law applies only to genes on different, nonhomologous chromosomes or those far apart on the same chromosome genes located near each other on the same chromosome tend to be inherited together Probability Laws the multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities the addition rule states that the probability that any one of two more exclusive events will occur is calculated by adding together their individual probabilities