Lecture 1-Ch 2
Lecture 1-Ch 2 30156
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This 7 page Class Notes was uploaded by Hannah Kennedy on Saturday July 23, 2016. The Class Notes belongs to 30156 at Kent State University taught by Dr. Helen Piontkivska in Spring 2016. Since its upload, it has received 43 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
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Date Created: 07/23/16
© Hannah Kennedy, Kent State University th Lecture 1—July 18 : Ch. 2, Reproduction and Chromosome Transmission 1. General features of chromosomes a. Key terminology: i. Chromosomes = the structures within living cells that contain the genetic material. Genes are physically located within the structure of chromosomes.. Biochemically, chromosomes contain a very long segment of DNA, which is the genetic material, and proteins, which are bounds to the DNA and provide it with an organized structure ii. Chromatin = the association between DNA and proteins that is found within chromosomes iii. Prokaryotes = pre-nucleus = bacteria and archaea; chromosomes aren’t contained within a membrane-bound nucleus of the cells. Have a single type of circular chromosome in the nucleoid iv. Nucleoid = a darkly staining region that contains the genetic material of mitochondria, chloroplasts, or bacteria v. Eukaryotes = true nucleus = 1 of the 3 domains of life. A defining feature of these is that their cells contain nuclei bounded by cell membranes b. Eukaryotic chromosomes are inherited in sets i. Key terminology: 1. Diploid = an organism or cell that contains 2 copies of each type of chromosomes (2 sets of chromosomes); most eukaryotic species are diploid 2. Homolog = 1 of the chromosomes in a pair of homologous chromosomes; in each pair, 1 homolog is from mom and 1 is from dad 3. Allele = an alternative form of a specific gene 4. Homozygous = describes a diploid individual that has 2 identical alleles of a particular gene 5. Heterozygous = describes a diploid individual that has different copies of the same gene 6. Locus = the physical location of a gene within a chromosome 2. Mitosis and meiosis: key processes for cells to transmit their genetic material a. Mitosis = cellular reproduction, making identical copies b. Meiosis = sexual reproduction, making diff versions of the cell 3. Organisms are composed of cells: Eukaryotes vs. prokaryotes a. Key terminology: i. Organelles = a large specialized structure within a cell that is surrounded by a single or double membrane Prokaryotes Eukaryotes - Cells contain nuclei bounded by cell - Chromosomes aren’t contained within membranes a membrane-bound nucleus - No cell wall - Cell wall - Need to export their transcripts - Have transcription and translation at 1 © Hannah Kennedy, Kent State University the same time - Have membrane-bound organelles - Have some membrane-bound (some of which have their own DNA organelles (chloroplast contain own like mitochondria) DNA) b. One activity that cells do is cell division which results in population of cells i. They create clones of identical cells during division ii. Asexual reproduction = a form of reproduction that doesn’t involve the union of gametes; at the cellular level, a preexisting cell divides to produce 2 new cells iii. Mother cell = original cell iv. Daughter cells = 2 new separate cells 4. Cell cycle a. Key terminology: i. Cell cycle = in eukaryotic cells, a series of stages through which a cell progresses in order to divide ii. Interphase = the series of phases G1, S, and G2, during which a cell spends most of its life iii. G0 = a stage in which a cell will enter when it remains either permanently or for a long time iv. Restriction point = a point in the G1 phase of the cell cycle that causes a cell to progress to cell division v. Chromatid = following chromosomal replication in eukaryotes, the 2 copies that remain attached to each other in the form of sister chromatids vi. Sister chromatids = pairs of replicated chromosomes that are attached to each other at the centromere. They are genetically identical. vii. Kinetochore = a group of cellular proteins that attach to the centromere during meiosis and mitosis viii. Mitosis = a type of nuclear division into 2 nuclei, such that each daughter cell receives the same complement of chromosomes ix. Mitotic spindle apparatus = mitotic spindle = the structure that organizes and separates chromosomes during M phase of the eukaryotic cell cycle; involved in the organization and sorting of chromosomes; has 3 types of MTs: asters (position spindle apparatus), polars (separation of the 2 poles), kinetochores x. Microtubule-organizing center = a site in a cell where microtubules begin to grow; spindle apparatus is formed from this xi. Centrosome = a cellular structure from which microtubules emanate; two MTOC xii. Spindle pole = 1 of 2 sites in the cell where microtubules originate and the centrosome is located xiii. Centrioles = a pair of cylindrically shaped structures found at the centrosome xiv. Prophase = the 1 stage of M phase in which the chromosomes have already replicated and begin to condense. The mitotic spindle starts to form 2 © Hannah Kennedy, Kent State University nd xv. Prometaphase = the 2 phase of M phase. During this phase, the nuclear membrane vesiculates, and the mitotic spindle completely formed. xvi. Metaphase plate = the plane at which chromosomes align during metaphase rd xvii. Metaphase = the 3 stage of M phase in which the chromosomes align along the center of the spindle apparatus xviii. Anaphase = the 4 stage of M phase in which ½ of the chromosomes move to 1 pole, and the other ½ move to the other pole xix. Telophase = the 5 stage of M phase in which the chromosomes have reached their respective poles and decondense xx. Cytokinesis = the division of a single cell into 2 cells. The 2 nuclei produced in M phase are segregated into separate daughter cells during cytokinesis b. The number of chromosomes and discrete DNA molecules changes c. Stages i. Interphase: decondensed chromosomes 1. G1 = growth phase (5 hrs) a. Have 2 homologous chromosomes b. Cell prepares to divide c. May accumulate molecular changes like the synthesis of proteins that causes it to progress through rest of cycle 2. G0 = nondividing cells 3. S = DNA replication (7 hrs) a. Have 2 homologous chromosomes with twice as much DNA in the cell (chromosomes are replicated) b. Cell has twice as many chromatids once completed than in G1 4. G2 = checkpoint (3 hrs) a. Makes sure DNA is replicated properly b. Cell collects materials needed for nuclear and cell division ii. Mitosis—division and distribute (M phase) (1 hr) 1. Prophase a. Chromosomes shorten and thicken b. Chromosomes have replicated to produce 12 chromatids and joined as 6 pairs of sister chromatids c. Nuclear membrane starts to dissociate d. Chromatids condense e. Mitotic spindle starts to form f. Nucleolus disappears (site of ribosome assembly) 2. Prometaphase—early metaphase (transition) a. Nuclear envelope breaks down b. Mitotic spindle is completely formed 3. Metaphase a. Chromosomes align at metaphase plate b. Chromatids can now be equally distributed into 2 daughter cells 4. Anaphase 3 © Hannah Kennedy, Kent State University a. Sister chromatids separate, become daughter chromosomes, and move to opposite poles of the spindle 5. Telophase a. Chromosomes decondense b. Nuclear membranes re-form and produce 2 separate nuclei 6. Cytokinesis a. 2 nuclei are segregated into separate daughter cells b. segregates cell organelles c. cleavage furrow forms that pinches 1 cell into 2 iii. Number of chromosomes in… 1. G1 = 4 = 2n 2. S = 4 = 2n 3. G2 = 4 = 2n 4. Prophase and prometaphase = 4 = 2n 5. Metaphase = 4 = 2n 6. Anaphase = 8 = 4n 7. Telophase and cytokinesis = 4 = 2n 5. Overview of cellular DNA a. 2 sister chromatids = identical copies of the same chromosome 6. Chromosome types a. Chromosomes are distinguished based on length and centromere location (chromosome 1 is the longest and 22 is the shortest) Name Location of Centromere Metacentric Middle Submetacentric Between the middle and the end Acrocentric Close to end p arm = small arm q arm = long arm Telocentric At the end 7. Karyotyping (Giemsa staining): based on different chromosome compositions a. Key terminology: i. Cytogenetics = the field of genetics that involves the microscopic examination of chromosomes ii. Somatic cell = any cell of the body except for germ-line cells that give rise to gametes iii. Gametes = a haploid reproductive cell that can unite with another reproductive cell to create a zygote (sperm and egg cells) 4 © Hannah Kennedy, Kent State University iv. Germ cells = the gametes = egg and sperm cells v. Karyotype = a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell b. Karyotyping basis: When a cell is preparing for division, they increase their diameter when shortening which gives them distinctive shapes and they become visible with a light microscope i. Karyotyping procedure: 1. Somatic cells are removed from the body → treated with drugs that stimulate them to begin dividing→ cell division is halted during mitosis → centrifuge to concentrate them → concentrated portion is mixed w hypotonic soln to make cells swe→l chromosomes spread out within cell to allow us to see them easier → cells treated with fixative that freezes them so they can’t move → cells are treated with dye that binds to chromosomes and stains them to give them the banding pattern a. Dark G-bands = heterochromatic regions = AT-rich regions i. Very few genes, replicate late, genes not expressed as often b. Lighter bands = euchromatic regions = GC-rich regions i. Have a lot of genes, replicate early, genes more often expressed c. Why we should know chromosome structure and identity: to differentiate between normal and abnormal karyotypes (i.e. medical genetics) i. Changes in number of chromosomes 1. Trisomy = extra chromosome 2. Monosomy = lost chromosome ii. Changes in chromosome structure such as a lost region, an extra region, or a rearrangement 1. Ex: 9:22 translocation is responsible for Chronic Myeloid Leukemia d. Homologous chromosomes have diff alleles at the same locus aka location 8. Meiosis = 2 successive nuclear divisions that results in 4 daughter cells; diploid to haploid a. Key terminology: i. Meiosis = a form of nuclear division in which the sorting process results in the production of haploid cells from a diploid cell ii. Haploid = phenomenon in which the gametes contain half the genetic material found in somatic cells. For a species that is diploid, a haploid gamete contains a single set of chromosomes b. Prophase 1 (3 stages): homologous chromosomes form pairs which leads to crossing over and recombination i. Leptotene stage: homology search: pairing of homologs begins; replicated chromosomes begin to condense ii. Sygonema (Zygotene): homologous chromosomes recognize each other and begin to align themselves; synaptonemal complex forms between the homologs. 1. Bivalents = a structure in which 2 pairs of homologous sister chromatids have synapsed aka aligned with each other a. the # of bivalents is equal to the number of haploid chromosomes 2. synapsis = the event in which homologous chromosomes recognize each other and then align themselves along their entire lengths 5 © Hannah Kennedy, Kent State University 3. synaptonemal complex = a complex of proteins that promote the interconnection between homologous chromosomes during meiosis iii. Pachynema: 2 pairs of sister chromatids close to each other, getting ready for genetic exchange 1. Tetrad = the association among 4 sister chromatids during meiosis 2. genetic exchange = crossing over = leads to an exchange of genetic material due to non-sister chromatids swapping it; if something goes wrong we will get a defect 3. chiasmata = the site where crossing over occurs between 2 chromosomes c. Meiosis I: continues as mitosis i. Prometaphase I ii. Metaphase I 1. Bivalents are organized along the metaphase plat; pairs of sister chromatids are aligned in a double row iii. Anaphase I 1. 2 pairs of sister chromatids within a bivalent separate from each other 2. homologous pair of chromatids moves to opposite pole iv. Telophase I and cytokinesis—reduction division 1. Sister chromatids have reached their respective poles 2. Decondensation 3. Nuclear membrane may re-form to produce 2 separate nuclei 4. Results in 2 cells d. Meiosis II: results in 4 haploid gametes—sorting events i. Metaphase II ii. Anaphase II iii. Telophase II iv. Haploid gametes e. Relevance: mistakes in meiosis lead to chromosomal abnormalities (i.e. medical genetics) i. Down syndrome (trisomy 21), turner syndrome (monosomy of X chromosome), klinefelter (XXY) ii. Cri du chat (deletion of 5p), Wilms tumor (interstitial deletion of 11p), normal phenotype (pericentric inversion 9) 9. Gamete formation: differences in division driven by the needs of the sexes for genetic material and energy source a. Key terminology: i. sexual reproduction = process whereby parents make gametes (sperm and egg) that fuse with each other in the process of fertilization to begin the life of a new organism ii. gametogenesis = the process by which haploid gametes are made 1. haploid = n (i.e. single set of chromosomes) 2. diploid = 2n (i.e. 2 pairs of chromosomes) 3. n = number of chromosomes (i.e. 2 sister chromatids) iii. isogamous = describes a species that makes morphologically similar gametes (e.g. fungi and algae) 6 © Hannah Kennedy, Kent State University iv. heterogamous = describes a species that produce 2 morphologically diff types of gametes (i.e. most eukaryotic species) b. Oogenesis = the production of egg cells that occurs within the oogonia i. Oogonia = specialized diploid cells of the ovary that initiate meiosis to produce primary oocytes 1. Primary oocytes are arrested at prophase I until the female becomes sexually mature at which point they’re periodically activated to progress through remaining stage of oocyte development ii. Meiosis makes only 1 cell that will become the egg (instead of 4 gametes produced from each primary spermatocyte during spermatogenesis) 1. First meiotic division is asymmetrical to make a secondary oocyte and a polar body. Cytoplasm is retained by secondary oocyte and not a lot by the polar body so that the oocyte can become a larger cell w more nutrients a. Secondary oocyte is released from ovary in ovulated and travels down oviduct to the uterus i. If sperm penetrates, secondary oocyte completes meiosis II and produces haploid egg and second polar body ii. Haploid egg and sperm nuclei unit to make diploid nucleus of individual iii. in rounds of division in which one chromatid hogs the cytoplasm and the rest are dumped out as a polar body to enable the oocyte to take the cytoplasm with itself (unequal division: out of 4 possible chromatids, only 1 gets to be the egg) iv. Process: Oogonium → (growth/maturation) → primary oocyte → (Meiosis I)→ secondary oocyte and 1 polar body → (meiosis II)→ ootid and 2dpolar body → (differentiation) ovum → c. Spermatogenesis = the production of sperm that occurs within the testes glands i. Spermatogonial cells divide by mitosis to produce 2 cells: 1 of which remains a spermatogonial cell and the other of which becomes a primary spermatocyte ii. Every chromatid has an equal chance of becoming a sperm early on (equal division) 1. Process: Spermatogonium → (growth/maturation) → primary spermatocyte → (meiosis I)→ secondary spermatocytes → (Meiosis II→ spermatids → (differentiation→ spermatozoa 7
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