Bio 101 Exam 2 Study Guide CHAPTER 8 Mitosis and Meiosis Cells Somatic Cells typical human body cells that have 46 chromosomes diploid Gametes have a single set of 23 chromosomes 22 autosomes and 1 sex chromosome only cells in human body not produced by mitosis 1 Describe the cell cycle with attention to the state of chromosomes The Cell Cycle an ordered sequence of events that extends from when a cell is first Interphase the period of the cell cycle in which a cell spends the majority of its formed from a dividing parent cell until its own division into two cells time when a cell s metabolic activity is very high and cell performs normal functions has three subphases G 1 Phase the first gap S Phase involves the synthesis of DNA and is also known as DNA replication Chromatin the entire complex of DNA and proteins that makes up eukaryotic chromosomes in roughly equal amounts chromatin refers to the very extended form that chromosomes take when a cell is not dividing As cell prepares to divide chromatin coils up forming distinct and tight chromosomes visible under a light microscope G 2 Phase the second gap cell grows more as it completes preparation Mitotic Phase M Phase interval of cell cycle when cell physically divides only for cell division accounts for 10 of cell cycle Mitosis on a continuum but 5 main stages distinguished Prophase changes occurring in nucleus and cytoplasm In nucleus chromatin fibers become more tightly coiled in nucleus and discrete chromosomes can be seen Each chromosome is two sister chromatids joined together mitotic spindle begins to form microtubules grow out Prometaphase nuclear envelope breaks into fragments and disappears microtubules emerging from centrosomes at end of mitotic spindle extend to the nuclear region reaching the chromosomes Each sister chromatid has a protein structure called a kinetochore at a specific DNA region within the centromere Some of the spindle microtubules attach to the kinetochores and move the chromosomes with the help of other microtubules toward the center of the cell Metaphase mitotic spindle is fully formed with poles at opposite ends of the cell Chromosomes line up on imaginary plate kinetochores of two sister chromatids are attached to microtubules from opposite poles Anaphase begins when the two centromeres of each chromosome come apart separating the two sister chromatids Motor proteins of the kinetochores powered by ATP move separated chromatids along the microtubules to opposite ends of the cell and each end has equal number of chromosomes Microtubules attached to kinetochores shorten but those not attached lengthen elongating the cell Telophase cell elongation that began in anaphase continues and nuclear envelopes begin to form around chromosomes leading to daughter nuclei at the poles By the end of this phase chromatin fibers uncoil and mitotic spindle disappears Mitosis is finished Telophase in animal cells cleavage furrow in plant cell wall thing Cytokinesis division of the cytoplasm that usually occurs simultaneously with 2 Relate the terms DNA molecule chromatin chromosome chromatid haploid and diploid homologous chromosomes non sister chromatids locus gene and allele to mitosis and meiosis DNA molecules replicated during S phase of Interphase Chromatin the entire complex of DNA and proteins that makes up eukaryotic chromosomes in roughly equal amounts chromatin refers to the very extended form that chromosomes take when a cell is not dividing Chromosome a gene carrying structure found in the nucleus and most visible during mitosis and meiosis consists of one very long DNA molecule and associated proteins Chromatid set of two chromosomes that are copies of one another Haploid in the life cycle of an organism that reproduces sexually a cell containing a Diploid In an organism that reproduces sexually a cell containing two homologous Homologous Chromosomes the two chromosomes that make up a matched pair in a single set of chromosomes an n cell Diploid cells meiose into haploid cells sets of chromosomes one set inherited from each parents a 2 n cell diploid cell They are the same length centromere position and staining pattern and possess genes for the same characters at corresponding loci One homologous chromosome is inherited from the mother and the other from the father chromosomes have corresponding gene loci Non sister chromatids Locus the particular site where a gene is found on a chromosome Homologous Gene a discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA or RNA in some viruses Most of the genes of a eukaryote are located in its chromosomal DNA a few are carried by the DNA of mitochondria and chloroplasts Allele an alternative version of a gene 3 Compare cytokinesis in animal and plant cells In animal cells cytokinesis occurs by cleavage Cleavage furrow a shallow groove in the cell surface that forms on an animal cell where the cell will divide in two At the site of this furrow cytoplasm has a ring of microfilaments made of actin that contract like drawstrings of a hoodie to divide the cell In plant cells there is a cell plate Cell plate During telophase membranous vesicles form golgi apparatus rough er etc collect at the middle of the parent cell fuse and form a disk called a cell plate plate grows outward accumulating more cell wall materials and eventually fuses with plasma membrane and parental cell wall 4 Explain why sexual reproduction requires meiosis how meiosis introduces variation Independent Orientation the manner in which homologous chromosomes line up at metaphase determines which chromosome will be distributed into which gamete There is a fifty percent chance a particular daughter cell will get the maternal chromosome of a pair and a 50 chance it will get the paternal chromosome Many Possibilities The total number of chromosome combos that meiosis can produce is 2 n where n haploid number For humans this means there are 2 23 or 8 million possible chromosome combinations for each gamete you produce Tetrad Organization homologous chromosomes can bear two different kinds of genetic information for the same characteristic i e coat color this is what makes gametes offspring different from one another Crossing Over exchange of corresponding segments between non sister chromatids of homologous chromosomes happens in early prophase I of meiosis Chiasma the sites of crossing over that appear as X shaped regions Process DNA molecules of two non sister
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