Gbio 106 1st Edition Final Exam Study Guide LECTURE 17 Cell Division and Genetics Eukaryotic Chromosomes DNA winds around proteins to form chromosomes Only visible during cell division and otherwise remain in chromatin form There are 23 pairs of chromosomes 46 single in human cells Homologous chromosomes are pairs of chromosomes that contain genes of the same traits Cells that contain pairs of each chromosomes are diploid Sex cells are haploid cells and only contain one of each chromosome Binary fission occurs in bacteria DNA occurs in one loop and the loop copies itself Cell splits with one loop in each new cell Bacterial growth starts slow and then by the time the cells multiply enough it spreads quickly Eukaryotic Cell Reproduction Occurs in protists fungi and animals Cells have a nucleus and store DNA Two types of nuclear division Mitosis Happens in body cells somatic cells Mitosis occurs when a parent cell divides to make an identical cell Responsible for growth and maintenance Meiosis The Cell Cycle Interphase and Mitosis In order for a cell to divide it must replicate its DNA and divide its nucleus and cytoplasm Interphase Takes up 90 of the cell cycle Can t be seen pretty boring DNA is invisible But in G1 the cell is growing In synthesis s phase DNA is replicated Then in G2 the cell prepares for mitosis PMAT DNA is our genetic code It is the molecule responsible for coding for the traits we have as well as what species we are All of our cells contain the same DNA Adenine and Thymine bond as well as Guanine with Cytosine DNA Replication 2 original strands of DNA unwind and separate to expose their n bases Each parental strand is used as a template Eventually each DNA strand and its newly formed strand wind together to form 2 new DNA molecules Copies are wrapped around protein and make chromosomes All 23 pairs Centromere holds pairs of chromosomes together Mitosis Prophase is where we first see chromosomes Microtubules form spindle fibers Nucleus starts to dissolve freeing the chromosomes The fibers attach to the centromere and grab sister chromatids LECTURE 18 Mitosis Continued Copying of body cells Growing maintenance and repair Nuclear division in which the chromosome number is maintained from one generation to the next Consists of four phases Interphase first See last lecture Prophase Chromatin condenses into visible chromosomes called sister chromatids Microtubules form spindle fibers and the nuclear membrane dissolves This frees the duplicated chromosomes This is when chromosomes first appear Metaphase Sister chromatids line up in the middle of the cell alone the metaphase plate Anaphase Chromosomes migrate toward opposite poles of the cell Telophase Individual chromosomes reach opposite ends of the cells The spindle apparatus begins to break down unravelling the chromosomes The nuclear membranes reform Chromosomes decidedness unwind back into chromatin form Two separate nuclei are formed with identical genetic information Actin filaments contract and pinch the cell in half Cytokinesis Cytokinesis Occurs in telophase and after telophase The cell pinches and forms a cleavage furrow eventually dividing in half Meiosis is a two staged form of cell division that occurs in reproductive organs that produce haploid daughter cells sex cells and contain one copy of each chromosome Spermatogenesis Production of sperm Oogenesis Production of egg ovum Gametes Sex cells Female egg holds the organelles and cytoplasm Don t want pairs in sex cells Meiosis 1 separates the pairs Meiosis then splits the sister chromatids apart so nothing results in pairs Meiosis 1 Prophase 1 Chromatin condenses into visible chromosomes Spindle fibers form The nuclear membrane dissolves Synapsis occurs the pairing of homologous chromosomes This forms a tetrad Crossing over may occur where segments of DNA are exchanged between non sister chromatids This crossing over creates unique combinations of genetic material Creates genetic variation Meiosis 1 Metaphase 1 Tetrads line up along the metaphase plate The positioning of each homologous pair of chromosomes during Metaphase 1 is a matter of chance The arrangement of chromosomes at Metaphase 1 will dictate which chromosomes will be packaged together in the sex cells Adds another level of variation Meiosis 1 Anaphase No pairs allowed Meiosis 1 Telophase Two cells with half of what we started with Still have sister chromatids though Meiosis 1 is just the reduction of chromosome number So begins Meiosis 2 Meiosis 2 Everything basically happens again Boring Not being tested on this process LECTURE 19 Random Fertilization Creates genetic variation randomly combined sperm and egg Non disjunction The failure of 1 or more chromosomes to separate during cell division Down s Syndrome 3 copies of the 21st chromosome Turner s Syndrome Monosomy missing female chromosome Genetics Study of patterns of inheritance Heredity The study of the passage of traits from parents to offspring Monohybrid cross Inheritance of one trait Alleles Alternate forms of one gene Dominant highest probability of being expressed NOT most commonly expressed Recessive Masked by dominant Locus Location of a gene on a chromosome Law of Segregation For every trait there are 2 alleles and these separate and recombine randomly through inheritance LECTURE 20 Dihybrid cross Study of two traits at one time For example using pea color and pea shape Independent assortment Chromosomes independently arrange themselves during Metaphase 1 Why do gens separate independently Because the genes for the two traits are on different chromosomes Gene linkage Tendency for genes to be located on the same chromosome and therefore to be inherited together Linked genes do not follow Mendel s law so they cannot independently assort Incomplete dominance Blending A pure red and a pure white snapdragon create a pink flower Pleiotropy One gene effects many traits PKU causing brain damage and mental retardation Epistasis Genes for two different traits that will mask the expression of the alleles of another gene LECTURE 21 SEX LINKED TRAITS Usually skip a generation