Genetics Exam 1 The Basics Nucleolus the initial stages of ribosomal assembly occur o a component where rRNA is synthesized and where o The areas that encode rRNA are collectively called Endoplasmic Reticulum ER the nucleolus organizer region NOR o Increase SA for biochemical synthesis o Smooth serves as the site for synthesizing o Rough rough because has ribosomes fatty acids and phospholipids ribosomes serve as the site where genetic information in mRNA is translated into proteins Centrioles o A pair of complex structures that are associated with the organization of spindle fibers that function in mitosis and meiosis o Located in the centrosome o Play an important role in the movement of chromosomes as they separate during cell division Spindle Fibers Homologous Chromosomes o Composed of arrays of microtubules o Nearly all chromosomes exist in pairs o Each chromosome has an identical twin with the same specific length and centromere placement Non Homologous Chromosomes o Chromosomes that are not members of the same pair Diploid Number 2n Haploid Number n o For example humans have a diploid number of 46 but a haploid number of 23 There are 23 pairs of chromosomes The total number of chromosomes is the diploid number and the total number of pairs is the haploid number Considers the sex cells a pair even though they aren t technically homologous o The information contained in a haploid set of chromosomes constitutes the genome Sister Chromatids o Each of the pairs has two chromosomes but each individual chromosome has a double structure connected in the center by a centromere Each part of the double structure is a sister chromatids Alleles o Different alternative forms of the same gene existing in a population of members of the same species Crossing Over Tetrad o During prophase I of meiosis o Within a homologous pair of sex cells the tips of 2 of the sister chromatids from different chromosomes cross over and exchange similar genes aka Different alleles o Once finished the chromosome from the mother has a piece from the father and the chromosome from the father has a piece from the mother o When crossing over the tips of the sister chromatids touch and create a bivalent structure of four sister chromatids known as a tetrad Chiasma o A point where nonsister chromatids have undergone genetic exchange through the process of crossing over Recombination o The process that leads to the formation of new gene combinations on chromosomes Synaptonemal Complex o An organelle consisting of a tripartite nucleoprotein ribbon that forms between the paired homologous chromosomes in meiosis I May be essential to crossing over The Cell Cycle 1 Interphase Characterized as the absence of visible Intensive metabolic activity cell growth and cell differentiation occurs chromosomes Chromatin Fibers Loosely packed uncoiled Made up of 3 different sub stages 1 G1 a Cell growth b Decision to make i Go into G0 or commit to ii Cancer cells avoid or go completing the cycle through G0 quickly 2 S phase a Replication of chromosomes b Centrioles replicate i Outside of nucleus ii Inside the centrosome an area of differentiated cytoplasm c DNA is synthesized 3 G2 a grows more size doubles 2 Mitosis Leads to the production of two cells each with the same number of chromosomes as the parent The hereditary components are equally divided into daughter chromosomes Made up of 5 different sub stages 1 Prophase a Chromatin condenses and chromosomes become visible i Each chromosome is now made up of two part connected at the centromere chromatid together are ii Each part is called a known as sister chromatids b The pair of centrioles migrate to opposite ends of the cell i Organize microtubules into spindle fibers to provide an axis for chromosome alignment ii c Nuclear envelop starts to dissolve 2 Pro metaphase a Microtubules attach to b Chromosomes move to the centromeres of chromosomes at the kinetochore equatorial plane metaphase plate 3 Metaphase a Full aligning of chromosomes after their migration to the equatorial plane 4 Anaphase 5 Telophase a Sister chromatids each separate to opposite poles b Each piece is now known as a daughter chromosome c 46 chromosomes at each pole one complete set at each pole a Nuclear envelop forms around each full set of chromosomes at each pole and become chromatin b Chromosomes begin to unwind c Spindle fibers disappear d Nucleolus reappears e Cytokinesis then cleaves the cytoplasm to give 2 haploid cells that are ready for Interphase 3 Meiosis Reduces the genetic content and the number of Leads to the production of sex cells gametes or chromosomes to half spores 2 different divisions each with it s own stages Meiosis I o Prophase I Chromatin condenses into visible Members of each homologous pair of chromosomes chromosomes undergo synapsis doesn t happen in mitosis Crossing over Within the tetrad during crossing over each pair of sister chromatids begins to separate but some areas stay in contact this area is known as a chiasma o Metaphase I The first division The chromosomes have fully condensed The terminal chiasmata of each tetrad are visible and appear to be the only factor holding the nonsister chromatids together o Anaphase I of each tetrad the dyad is pulled toward each pole of the dividing cell At the completion a series of dyads equal to the haploid number is present at each pole Nuclear membrane develop around the After completion the nucleus enters a o Telophase I dyads short interphase but NO DNA replication before meiosis II Each dyad is composed of one pair of sister chromatids attached by a common centromere o Metaphase II The centromeres are positioned on the When they divide anaphase II is metaphase place initiated o Anaphase II Meiosis II o Prophase II o Telophase II Sister chromatids of each dyad are pulled to opposite poles One member of each pair of Cytokinesis to reveal 4 haploid homologous chromosomes at each pole gametes Mendelian Genetics Mendel determined that discrete unit of inheritance exist and he predicted their behavior during the formation of gametes Mendel s postulates were accepted as the basis for the study of what is known as transmission genetics Monohybrid Cross o Only one pair of contrasting traits o Mating true breeding individuals from two parents strains each exhibiting one of the two contrasting forms of the character under study First Filial Generation F1 F1 Hybrid Parental Generation P1 o The original parents o Offspring from the original
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