BIOL 1441 1st Edition Lecture 22 Outline of Last Lecture I Cyclins and Cyclin dependent kinases II Cell growth cancer genes III Meiosis IV Gamete production V nondisjunction Outline of Current Lecture I Meiosis II Stages of Meiosis I III Stages of Meiosis II IV Meiosis and diversity V Heredity VI Chromosomes somatic cells gametes VII Twins VIII Asexual sexual reproduction IX Genetic variation Current Lecture I Meiosis a Gametes go through cell cycle like mitosis i Meiosis is preceded by the replication of chromosomes b Meiosis two sets of cell divisions These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II i Meiosis I meiosis II ii Mitosis one cell division c Meiosis results in 4 nonidentical daughter cells i Mitosis results in 2 identical daughter cells d Diploid 2n cells that contain 46 chromosomes i Somatic cells e Haploid n cells that contain 23 chromosomes i Gametes sex cells Stages of Meiosis I a Meiosis I homologous chromosomes separate chromosome pairs not sister chromatids i 92 46 b Results in two daughter cells with replicated chromosomes sister chromatids i Diploid 46 chromosomes c Homologous Chromosomes pairs of chromosomes with same genetic material but not identical i Pair of individual chromosomes one from mom one from dad NOT sister chromatids d Division in meiosis I occurs in four phases i Prophase I 1 Chromosomes condensed 2 Spindle formation nuclear envelope breaking down 3 Genetic recombination 4 Synapsis homologous chromosomes align gene by gene 5 Crossing over chromosomes break apart non sister chromatids exchange DNA segments a Enzyme snips in half and fuses DNA opposite of each other b Only the 2 homologs in the center cross over 6 Chiasmata criss crossed regions of DNA holding homologous chromosomes together 7 90 of the time 8 Tetrad group of four sister chromatids 9 Each tetrad has one or more chiasmata 10 Late prophase microtubules attach to kinetochores of the chromosomes ii Metaphase I 1 Tetrads line up on metaphase plate with one chromosome facing each pole 2 Genetic recombination place 2 iii Anaphase I 1 Chromosome moves toward opposite poles guided by the spindle apparatus III IV V 2 Sister chromatids remain attached at the centromere move as one unit toward the pole 3 Pairs of homologous chromosomes separate iv Telophase I Cytokinesis 1 Each cell contains sister chromatids 2 Cytokinesis usually occurs simultaneously 3 Animals cleavage furrow forms 4 Plants cell plate forms Stages of Meiosis II a Separation of sister chromatids b 4 phases i Prophase II 1 Spindle apparatus forms 2 Late prophase II chromosomes each still composed of two chromatids move toward the metaphase plate ii Metaphase II 1 Kinetochores of sister chromatids attach to microtubules extending from opposite poles 2 Sister chromatids line up on metaphase plate a No longer genetically identical iii Anaphase II 1 Sister chromatids separate 2 Sister chromatids of each chromosome now move as individual chromosomes toward opposite poles iv Telophase II Cytokinesis 1 Nuclei form 2 Chromosomes begin decondensing 3 Cytokinesis separates the cytoplasm 4 4 n haploid daughter cell nonidentical Meiosis Diversity a Genetic diversity is essential for life b Essential for survival of species c Species or ecosystem more diversity healthier population or system d Challenged with environmental pressures i Different genes selected for ii Natural selection favorable genes you will most likely survive to pass that genetic information on Hereditary Similarity Variation a Heredity transmission of traits from one generation to the next b Genetics scientific study of heredity and variation c Genetic information is transferred by DNA d Genes segments of DNA units of heredity i Code for a protein physical trait eye color VI VII VIII IX e Inheritance of Genes i Each gene has a specific locus location on a certain chromosome ii One chromosome thousands of genes on it f Chromosomes in Human Cells i Chromosomes differ in size centromere position stain differently ii Karyotype ordered display of the pairs of chromosomes from a cell 1 23 pairs in somatic cells 46 total Chromosomes Somatic Cell a Autosomes 22 pairs of chromosomes that do not determine sex b 1 pair of sex chromosomes X and Y i Females XX ii Males XY c Chromosomes Gametes i Haploid cells n 23 ii 22 autosomes and a single sex chromosome iii Egg ovum sex chromosome is X iv Sperm cell the sex chromosome X or Y Twins a Identical monozygotic i 1 egg ii Divides into 2 separate embryos iii Random not hereditary b Fraternal dizygotic i 2 separate eggs ii Genetic component iii Yoruba Nigeria c Monozygotic twins split into 2 zygotes very early in the pregnancy d Timing of this separation determines the chorionicity and amniocity the number of sacs of the pregnancy i Dichorionic twins divide first 4 days ii Monoamnionic twins divide after 1st week e In very rare cases twins become conjoined twins if separation happens too late Asexual Sexual Reproduction a Asexual reproduction 1 parent produces genetically identical offspring by mitosis b Sexual reproduction 2 parents give rise to offspring that have unique combinations of inherited genes Genetic Variation a Mutations changes in an organism s DNA original source of genetic diversity b Mutations create different versions of genes c During sexual reproduction several occurrences create genetic variation i Independent assortment of chromosomes ii Crossing over iii Random fertilization d Independent Assortment of Chromosomes i Homologous pairs of chromosomes randomly line up at metaphase I of meiosis ii Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs e Crossing Over i Produces recombinant chromosomes 1 Combine genes inherited from each parent ii Begins very early in prophase I as homologous chromosomes pair up gene by gene iii Homologous portions of two nonsister chromatids trade places iv Contributes to genetic variation by combining DNA from two parents into a single chromosome f Random Fertilization i Any sperm can fuse with any egg 1 Remember meiosis produce 4 nonidentical haploid gametes due to independent assortment crossing over ii Fusion of gametes produces a zygote with any of about 64 trillion diploid combinations iii Each zygote has a unique genetic identity