Lecture 20 Outline of Last Lecture I. DNA and Cell ActivitiesII. TranscriptionIII. TranslationOutline of Current Lecture I. The Cell CycleII. Meiosis and Sexual Cell CyclesIII. Mendel and ChromosomesIV. The Molecular Basis of Inheritance Current LectureExam 3 ReviewI. The Cell Cycle- Terms: genome, chromatin, nuclear envelope, centromere, kinetochore, spindle, replicated chromosome, sister chromatid, metaphase plate o Matching, draw replicated chromosome- What is cytokinesis? o Division of cytoplasm- Be able to draw a cell in metaphase and label sister chromatids, kinetochore and spindleo Sister chromatids are held tightly together at centromere; kinetochore is the protein complex that the spindle apparatus attaches to- Possible discussion question: How do cancer cells differ from normal cells with regard to cell cycle control? will be on examo 3 basic ways: normal cells will divide a certain number of times (30-50 times) and then it will getold and die; cancer cells are mortal, they divide forever; in tissue culture, a normal cell will growuntil they touch one another (contact inhibition) and then they stop dividing; cancer cells keep dividing and pile up on each other (no contact inhibition); cancer cells USUALLY don’t stop dividing, but when they do, they stop at the wrong point and have the wrong amount of DNAII. Meiosis and Sexual Life Cycles BIOL 1st Edition- What are the two major kinds of reproduction and how do they differ from each other with regard to the offspring produced? o 2 ways: asexual  one parent, genetically identical to offspring and parent, basically cell division, not the best way to reproduce; sexual  2 parents, offspring are genetically unique- Terms to know – gamete, zygote, chromosome, homologous chromosomes (also called homologs or homologous chromosome pairs)o Matching section most likely; zygote is diploid 1st cell; chromosomes come in pairs in body cells- *haploid versus diploid* - several questions cover this concept (ex. If diploid number of an organism is 10, how many chromosomes are in the sperm cell? Or the body cells? Etc.o body cells are diploid cells CHROMOSOMES COME IN PAIRS; gametes (egg, sperm) are haploid cells have HALF AS MANY CHROMOSOMES; humans have 46 chromosomes in body cells 23 PAIRS, one from egg, one from sperm; if diploid number is 10, there are 5 chromosomes in sperm/eggo LOOK ONLINE FOR SCANNED QUIZ WITH EXAMPLES- What is meiosis? What is the purpose of meiosis? What kind of cell undergoes meiosis? (a germline cell undergoes meiosis. In humans, these are only found in the ovaries and testes) o Meiosis produces eggs and sperm; only Germline cells undergo meiosis  only job is to make gametes;- Given the diploid (2n) or haploid (n) number of an organism, be able to draw a cell of that organism in metaphase of mitosis, meiosis I and meiosis II WILL BE ON EXAMo 2N = 6  1N = 3; mitosis  all 6 chromosomes lined up single file on metaphase plate, meiosis I  3 pairs of 2 chromosomes line up 2 by 2 on the metaphase plate, meiosis II  replicated chromosomes line up 1 by 1 on the on metaphase plate, but only have 3 chromosomeso 2N = 8  1N = 4; mitosis  8 chromosomes single file, meiosis I  4 pairs of 2 lined up 2 by 2, meiosis II  4 chromosomes line up 1 by 1- Name three sources of genetic variation in sexual reproduction: independent assortment of chromosomes during meiosis, crossing over, random fertilization (multiple choice/fill in the blank)o Independent assortment  Maternal and paternal homologs line-up randomly, with no effect on any other pairso Crossing over  1 in 8 million possible combinations in egg AND sperm, 1 in 64 trillion possible combos.o Random fertilization  - Given the 2n or n # of an organism, be able to figure out the # of possible combinations of maternal and paternal homologs in the gametes (# of possible combinations = 2n, where n = haploid #)o 2N = 6  then 1N = 3 and then 23 = 8 possible combos; 1N = 8 million  2N = 64 million, then 223 = 64 trillion- What is crossing over? When does it occur? What is a meiotic tetrad?o 2 replicated chromosomes, then in meiosis they get close together and exchange DNA  tetrad = 4 pieces of DNA from the 2 replicated pieces of DNA; occurs in meiosisIII. Mendel and Chromosomes- Terms: “true-breeding”, allele, dominant, recessive, homozygous, heterozygouso matching or fill in the blank; true-breeding = monohybrid crosses with 2 pea plants that differedfrom one another by only one SINGLE trait; allele = alternative form of a gene (protein) located along a piece of DNA; dominant = expressed; recessive = unexpressed, must have 2 recessive to have it expressed; homozygous = both copies are the same; heterozygous = one of each- Mendel’s Law of Independent assortment: be able to give the possible combinations of alleles in the gametes of an individual who is heterozygous for TWO traits located on DIFFERENT chromosomes (think of foiling) ex. GgRr  GR, Gr, gR, gr o Traits only assort independently if they are on different chromosomes; gametes each get one of the homologous pairs - Genetic disorders in humans: (recessive disorders)-cystic fibrosis, sickle cell anemia; (dominant disorders)-dwarfism, Huntington’s (matching/ multiple choice) What does it mean to be a “carrier” of a recessive allele?o Definitely matching - Possible discussion: Why is the sickle cell trait so common in the African-American population? o Almost definitely on exam; this trait occurs with an advantage – resistance to malaria – so in Africa it was desired because if you carried it, you were resistant to malaria, keeping it at a high level in population- Complications of Mendelian genetics: incomplete dominance (also called intermediate inheritance), multiple alleles, epistasis, pleiotrophy, environmental factors) o matching/multiple choice - X-Y system of sex determination: know the terms homogametic sex and heterogametic sex. Which determines the sex of the offspring?o Homogametic sex = X gametes (female XX); heterogametic sex = X and Y gametes (male XY); behave as though they are homologous chromosome pairs but they don’t share many alleles- Know differences between X and Y chromosomes (multiple choice) Possible discussion questions: 1) Are any genes on the Y chromosome required for life? Why or why not? 2) What does the term “X-linked” mean?o No, impossible because women have XX