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UT Knoxville BIOL 240 - Exam 1 Study Guide

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BIOL 240 1st EditionExam # 1 Study Guide Lectures: 1 - 6Lecture 1 (January 9)Introduction to Chromosomes and the Cell Cycle. How are chromosomes separated into diploid cells? What is mitosis and what happens during it?Key Terms:1. Metacentric- when the centromere location is in the middle of the paired sister chromatids2. Submetacentric- when the centromere location is between the middle and the end of the paired sister chromatids3. Acrocentric- when the centromere location is close to the end of the paired sister chromatids4. Telocentric- when the centromere location is at the end of the paired sister chromatidsDiploid cells:a. Chromosomes are present in pairs of homologs, meaning that they are physically identical, but not genetically identical.b. One homolog from each parentc. Distinguishing feature of males and females are large gametes (egg) and smallgametes (sperm)Cell Cycle:1. Mitosisa. Interphase- chromosomes are distributed all throughout the nucleus; they are uncoiled and chromatin is formedb. Prophase- condensation of chromosomes; centrioles divide and begin to move apart; spindle begins to formc. Prometaphase- chromosomes are completely condensed and are evident double structures; centrioles reach opposite ends; spindle fibers formedd. Metaphase- centromeres align of the metaphase plate in the center of the cell; spindle microtubials are tugging on the chromosomese. Anaphase- centromere split and daughter chromosomes are segregated to opposite polesf. Telophase- nuclear envelop reformed and cytokinesis cleaves the cell into twog. Cohesion- during DNA replication, a ring shaped protein complec called cohesin is formed around the duplicated strands to hold the chromatids together through much of the cell cycle; once anaphase is reached, the enzyme separase cleaves the cohesin ringsh. Cytokinesis- division of the cytoplasm between daughter cells; driven by cleavage furrow formed in telophaseLecture 2 (January 12) What is meiosis and what happens during it?Meiosis I:1. Metaphase I: paired homologs align on the spindle centromeres facing opposite poles2. Anaphase I: sister chromatids still connected at their centromeres segregate to opposite poles; crossovers are regulated so that at least one occurs3. Telophase I: chromosomes reach opposite poles and cytokinesis begins to occur4. Prophase I: two haploid cells are producedMeiosis II (much like mitosis):1. Metaphase II: after Prophase I, centromeres align on the metaphase plate2. Anaphase II: sister chromatids are segregated to opposite poles3. Telophase II: chromosomes reach opposite poles and cytokinesis occurs; the products are 4 haploid gametes that are all genetically different due to homolog segregation and crossing-overHow are gametes produced? What is the difference between male and female gamete production?In male animal cells, cells derived from germ cells are called spermatogonium. Males have these cells up until the point when maturation (puberty) begins. Once this happens, the spermatogonium grow into primary spermatocyte, which undergoes the first division of meiosis. The products are two secondary spermatocytes, each containing a haploid number of dyads. Both of these then undergo the second meiotic division, producing a total of four (two from each) spermatids. Spermatids then undergo physical changes and form into spermatozoa, which is what is needed to fertilize a female gamete.In female animal cells, cells called oogonium form into primary oocytes, all of which are produced before birth. Once puberty is reached, the primary oocytes undergo the first meiotic division, products being a secondary oocyte and the first polar body. The secondary oocyte is what will go on to be fertilized, so it contains most of the cytoplasm in hopes of nourishing an embryo. The first polar body is discarded. Upon fertilization, the second meiotic division occurs and the secondary oocyte divides into an ootid and a second polar body. The ootid reforms intoan ovum and the second polar body is also discarded.Lecture 3 (January 14)How was chromosome segregation of alleles discovered?Mendel’s experiment:Why peas? Mendel chose to experiment with peas because they are easy to grow, possible to control self-fertilization or cross-fertilization, and they have observable and distinguishable characterisitcs.Experimented characteristics:a. Seed shape (round or wrinkled)b. Seed color (green or yellow)c. Pod shape (full or constricted)d. Pod color (green or yellow)e. Flower color (violet or white)f. Flower position (axial or terminal)g. Stem height (tall or dwarf)Mendel used controlled monohybrid crosses, which involved pairs of true breeding plants with only one differing characteristic. The first generation were true breeding (DD and dd) and were crossed. Their offspring resulted in all dominant characteristics (Dd), masking the recessive (dd).These were crossed and their offspring resulted in ¾ dominant and ¼ recessive; a 3:1 ratio. A visual is given below.Mendel discovered that reciprocal crosses gave the same result and sex is independent of the results. He concluded:a. Heredity is controlled by genes and traits are passed unchanged through generationsb. Organisms have two copies of each gene (alleles)- one from the mother and one from the fatherc. In the case that two alleles an organism has are different, one is dominant and the other is recessive.d. Law of Segregation: alleles separate and enter different gametes; gametes only receive one allele of each pairLecture 4 (January 16)Review of Mendel’s experiment:Mendel uses peas in his experiment; peas that are either yellow or green, round or wrinkled. First, he crossed all possible combinations of parents (yellow and round with green and wrinkled, AND yellow and wrinkled with green and round). In both cases, the offspring wereall yellow and round. Since they were all yellow and round, two were crossed together. The offspring resulted in a 9:3:3:1 ratio. Where did this come from?For each experiment Mendel conducted involving more than two pairs of contrasting traits, all of his crosses resulted in a 9:3:3:1 ratio. He concludes that different genes separate independently of each other. This is known as the Law of Independent Assortment. During gamete formation, genes segregate independently. For example, two parents with AaBb could produce AB, Ab, aB, or ab offspring with the same frequency.The Punnett Square is a helpful table that can help display all possibilities during


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