Objectives for Exam 1 PCB 3063 Summer 2012 Mitosis and Meiosis Chapter 2 Q Of basic importance in this material is to know the essential differences between mitosis and meiosis what homologous chromosomes are and how they behave in mitosis and meiosis Mitosis mitosis produces somatic cells all cells except for reproductive cells Mitosis produces 2 genetically identical daughter cells Mitosis does not change the number of chromosomes Each daughter cell gets 1 chromatid from chromosome New sister chromatid made for each chromosome Homologous Chromosomes PAIR DURING MEIOSIS The cell division that occurs as apart of the creation of gametes Sections of the DNA can sometimes cross over between homologous pairs Meiosis produces reproductive cells sperm and egg Formation of gametes One diploid cell divides twice and forms 4 haploid cells Each daughter cell gets one chromatid from each pair of homologous chromosomes 2n 4 n 2 Meiosis I First division homologous chromosomes separate into different daughter cells Crossing over occurs chromosome recombination Meiosis II Second division sister chromatids separate in to different daughter cells In MI MII DNA is first replicated and then different methods are used for separation of the replicated genetic information Before replication chromosomes exist as a single DNA double helix bound by histone proteins chromatin 2n 2 copies of each chromosome 2n 2 pairs of homologous chromosomes diploid of 4 2n 4 chromosomes Q Understand the concept of the cell cycle and know what happens during S phase G0 cell gets ready for DNA replication resting phase does not divide in this phase Interphase the chromosomes are un condensed cell grows the proceeds to G1 S and G2 phases G1 checkpoint makes sure everything is ready for DNA synthesis replication synthesis of enzymes and lots of growth S synthesis chromosome duplication occurs this phase is complete when each chromosome has 2 sister chromatids G2 cell is preparing structures like microtubules necessary for mitosis check point makes sure the cell is ready to enter cell division phase M phase Q Be able to name the stages of mitosis and know what events take place in each Mitosis cell growth stops here division into 2 daughter cells Prophase chromatin begins to condense and become visible centrioles start moving to opposite ends start of spindle formation coil Metaphase spindle fibers align the chromosomes along the metaphase plate align Anaphase the paired chromosomes separate at the kinetochore centromere and move to opposite sides of the cell separate Telophase new membranes form around daughter cells chromosomes uncondensed uncoil Cytokenisis the cells completely divide into two daughter cells Plants cell plate Sister Chromatids are exact duplicates a condensed chromosome ready for Q Know what sister chromatids are division mitosis Sisters have 2 arms Q Understand the haploid and diploid and know what homologous chromosomes are how they are similar to each other and how they differ from nonhomologous chromosomes Haploid n the number of chromosomes in a gamete Diploid 2n the number of chromosomes in a somatic cell Humans are diploid Humans contain 46 chromosomes 2 complete haploid sets which make up 23 homologous chromosome pairs Homologous Chromosomes carry the same genes but may have different alleles have same centromere position same length Non homologous chromosomes would carry completely different genes Exception sex chromosomes which are homologous chromosomes but don t carry the same genes Q Know the important events that occur in meiosis and understand how meiosis differs from mitosis Meiosis I Prophase 1 homologous chromosomes pair up and form synapses these paired chromosomes are called bivalents tetrads Metaphase 1 bivalents line up along the metaphase plate Anaphase I chiasmata separate chromosomes each with 2 chromatids move to separate poles Each of the daughter cells is now haploid 23 chromosomes but each chromosome has 2 chromatids Telophase I Cytokinesis I nuclear envelopes may reform or cell may go right into meiosis II 2 complete daughter cells form Meiosis II In metaphase II the chromatids separate and become independent chromosomes No DNA replication before meiosis II Everything else is pretty similar to Meiosis I except the chromosome number is not reduced Differences between mitosis and meiosis Chromosomes in meiosis undergo a recombination which shuffles the genes Crossing over results in different genetic combinations in each gamete Outcome of meiosis is 4 haploid cells all genetically unique compared with the two genetically identical diploid cells produced from mitosis In the first meiotic division the number of cells is doubled but the number of chromosomes is not results in 1 2 as many chromosomes per cell The second meiotic division is like mitosis the number of chromosomes does not get reduced At the end of division 1 each of 2 daughter cells has 2 chromosomes each with 2 chromatids and no pairs Second division 4 daughter cells each with 2 chromosomes each of these chromosomes only have 1 chromatid Q Be able state how many chromosomes and pairs of homologous chromosomes are present in cells of a given diploid number that are undergoing meiosis Understand the terms tetrad chiasmata crossing over and recombination Tetrad bivalents paired and replicated chromosomes 2 chromosomes 4 chromatids with 1 chromosome coming from each parent Chiasma the point where two homologous non sister chromatids exchange genetic material during chromosomal cross over during meiosis Crossing over exchange of genetic material between homologous chromosomes one of the final phases of recombination Recombination a process in which a molecule of DNA is broken and then joined to a different one Skill be able to solve genetics problems similar to those suggested as homework in chapter 2 and in the first quiz Review of Mendel s Principles Chapter 3 Q Be able to state Mendel s postulates Random Segregation and Independent Assortment and understand their significance Mendel s Postulates 1 Each trait is controlled by a pair of factors genes 2 When 2 different factors for a trait are present in an individual one is dominant and one is recessive alleles 3 During gamete formation the paired factors segregate randomly 4 Genes for different traits are inherited independently independent assortment Q Know and be able to use the terms phenotype genotype homozygous heterozygous dominant recessive allele true
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