General Biology. Overview: Hereditary Similarity and Variation Living organisms. Comparison of Asexual and Sexual Reproduction In asexual reproduction

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1 Course No: BNG2003" Credits: 3.00 " Geeral Biology " " 9. Meiosis ad Life Cycles Overview: Hereditary Similarity ad Variatio Livig orgaisms are distiguished by their ability to reproduce their ow kid Prof. Dr. Klaus Heese Geetics Heredity is the trasmissio of traits from oe geeratio to the ext Variatio shows that offsprig differ somewhat i appearace from parets ad sibligs is the scietific study of heredity ad hereditary variatio Offsprig acquire gees from parets by iheritig Iheritace of Gees Gees are the uits of heredity are segmets of DNA Each gee i a orgaism s DNA has a specific locus o a certai chromosome We iherit oe set of from our mother ad oe set from our father Compariso of Asexual ad Sexual Reproductio I asexual reproductio oe paret produces geetically idetical offsprig by mitosis Bud Paret 0.5 mm I sexual reproductio Two parets give rise to offsprig that have uique combiatios of gees iherited from the two parets Fertilizatio ad meiosis alterate i sexual life cycles A life cycle is the geeratio-to-geeratio sequece of stages i the reproductive history of a orgaism Sets of Chromosomes i Huma Cells i humas each somatic cell has 46, made up of two sets oe set of comes from each paret 1

2 Homologous Chromosomes The two, oe from each of your parets, which carry the iformatio for similar gees We get 23 from mom, 23 from dad What is a Allele? Alleles are alterative forms of a gee Oe allele for a gee carried o oe chromosome Chromosome ca have may, may gees Example: If you have type AB blood, you got the A allele from oe paret, the B allele from aother Diploid vs. Haploid Most huma somatic (body) cells have 46 This is called the diploid coditio 2 = 46 Gametes (sperms ad eggs) are a exceptio: they oly have 23 This is the haploid coditio = 23 Trick Questio We get 23 from our mom, ad 23 from our dad. Which 23 does each of us pass o to our childre? Aswer The 23 that we pass o to our offsprig, are each a medley of the 23 pairs of that we have. Hece, we pass o parts of both! Meiosis allows us to do this I a cell i which DNA sythesis has occurred all the are duplicated ad thus each cosists of two idetical sister 2 = 6 Two sister of oe replicated chromosome Materal set of ( = 3) Pateral set of ( = 3) Cetromere Two osister i a homologous pair Pair of homologous (oe from each set) 2

3 A Karyotype is a ordered, visual represetatio of the i a cell Karyotypig Pair of homologous Cetromere Sister 5 µm literally, a picture of your ca be used to detect some geetic abormalities too may, or too few Homologous are the two composig a pair have the same characteristics may also be called autosomes Sex are distict from each other i their characteristics are represeted as X ad Y determie the sex of the idividual, XX beig female, XY beig male A diploid cell has two sets of each of its i a huma has 46 (2 = 46) Trisomy 21: Dow s sydrome 3 copies of chromosome #21 preset May symptoms Roud face Flatteed ose Small, irregular teeth Short stature Heart defects Respiratory ifectio Leukemia Alzheimer s disease (APP o chr21) / similar symptoms XYY Extra Y chromosome Ofte taller Produces a otherwise ormal male Metafemale XXX Reduced fertility Otherwise ormal female 3

4 Ulike somatic cells gametes, sperm ad egg cells are, cotaiig oly oe set of Behavior of Chromosome Sets i the Huma Life Cycle At sexual maturity the ovaries ad testes produce haploid gametes by meiosis Durig fertilizatio these gametes, sperm ad ovum, fuse, formig a diploid zygote the zygote develops ito a adult orgaism The huma life cycle Haploid () Diploid (2) durig meiosis meiocytes produce Haploid gametes ( = 23) Sperm Cell () Ovum () Ovary Testis Diploid zygote (2 = 46) Multicellular diploid adults (2 = 46) ad developmet durig meiosis meiocytes produce The Variety of Sexual Life Cycles The three mai types of sexual life cycles differ i the timig of meiosis ad fertilizatio I aimals Meiosis occurs durig gamete formatio Gametes are the oly Haploid Diploid Gametes durig meiosis meiocytes produce 2 Zygote 2 Diploid multicellular orgaism (a) Aimals Plats ad some algae Exhibit a alteratio of geeratios The life cycle icludes both diploid ad haploid multicellular stages Haploid multicellular orgaism (gametophyte) I most fugi ad some protists Meiosis produces that give rise to a haploid multicellular adult orgaism The haploid adult carries out mitosis, producig cells that will become gametes Haploid multicellular orgaism Spores Gametes Gametes Diploid 2 multicellular orgaism (sporophyte) (b) Plats ad some algae 2 Zygote 2 Zygote (c) Most fugi ad some protists 4

5 Meiosis Basic Cocepts Two thigs achieved: Recombies the your parets gave you Produces haploid gamete cells, havig oly 23 Two Parts of Meiosis Meiosis I Meiosis II Both are similar to, but also differet from mitosis (---> see cell cycle, cell proliferatio) Meiosis I This step reduces Starts with diploid (2 = 46) cell Produces two haploid ( = 23) cells Meiosis II Starts with two Produces four These are 4 sperms or 4 eggs Also is where recombiatio occurs Meiosis reduces the umber of chromosome sets from diploid to haploid Iterphase ad meiosis I Meiosis takes place i two sets of divisios, meiosis I ad meiosis II Iterphase Homologous pair of i diploid paret cell Chromosomes replicate INTERPHASE I: Separates homologous PROPHASE I METAPHASE I ANAPHASE I The Stages of Meiosis A overview of meiosis Meiosis I reduces the umber of from diploid to haploid Meiosis II produces four haploid daughter cells Homologous pair of replicated Sister Meiosis I 1 Homologous Haploid cells with replicated Meiosis II 2 Sister Diploid cell with replicated Cetrosomes Cetromere Sister (with cetriole pairs) (with kietochore) remai attached Chiasmata Sister Metaphase plate Spidle Nuclear evelope Microtubule Homologous Tetrad Chromati attached to kietochore replicated (homologous) Chromosomes duplicate Tetrads lie up Pairs of homologous Homologous split up (red ad blue) pair ad exchage segmets; 2 = 6 i this example Haploid cells with ureplicated 5

6 Telophase I, cytokiesis, ad meiosis II II: Separates sister TELOPHASE I AND PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II AND CYTOKINESIS CYTOKINESIS Cleavage Haploid daughter cells furrow Sister formig A Compariso of ad Meiosis Meiosis ad mitosis ca be distiguished from mitosis by three evets i Meiosis l Syapsis ad crossig over Homologous physically coect ad exchage geetic iformatio Tetrads o the metaphase plate at metaphase I of meiosis, paired homologous (tetrads) are positioed o the metaphase plates Two form; are still double replicated Durig aother roud of cell divisio, the sister fially ; four haploid daughter cells result, cotaiig sigle Separatio of homologues: at aaphase I of meiosis, homologous pairs move toward opposite poles of the cell; i aaphase II of meiosis, the sister A compariso of mitosis ad meiosis MITOSIS Paret cell (before chromosome replicatio) Chiasma (site of crossig over) I Prophase Duplicated chromosome (two sister ) Chromosome replicatio Chromosome replicatio 2 = 6 diploid cell Prophase I Tetrad formed by syapsis of homologous Metaphase Chromosomes positioed at the metaphase plate Tetrads positioed at the metaphase plate Metaphase I Aaphase Telophase Sister durig aaphase 2 2 Daughter cells of mitosis diploid cells Homologues durig aaphase I; sister remai together Daughter cells of meiosis I Daughter cells of meiosis II Sister durig aaphase II Aaphase I Telophase I Haploid = 3 with replicated chr II = 3 Idepedet Assortmet of Chromosomes Homologous pairs of oriet radomly at metaphase I of meiosis I idepedet assortmet each pair of sorts its materal ad pateral homologues ito daughter cells idepedetly of the other pairs Materal set of Possibility 1 Pateral set of Possibility 2 Two equally probable arragemets of at metaphase I Metaphase II Daughter cells Combiatio 1 Combiatio 2 Combiatio 3 Combiatio 4 6

7 Crossig Over Crossig over Produces recombiat that carry gees derived from two differet parets Prophase I of meiosis Nosister Radom Fertilizatio the fusio of gametes will produce a zygote with ay of about 64 trillio diploid combiatios Evolutioary Sigificace of Geetic Variatio Withi Populatios Geetic variatio Metaphase I Tetrad Chiasma, site of crossig over is the raw material for evolutio by atural selectio Mutatios are the origial source of geetic variatio Metaphase II Sexual reproductio Daughter cells Recombiat produces ew combiatios of variat gees, addig more geetic diversity Geetic variatio produced i sexual life cycles cotributes to evolutio Reshufflig of geetic material i meiosis produces geetic variatio Origis of Geetic Variatio Amog Offsprig I species that produce sexually the behavior of durig meiosis ad fertilizatio is resposible for most of the variatio that arises each geeratio Takig home message: Epigeetics I biology, ad specifically geetics, epigeetics is the study of iherited chages i pheotype (appearace) or gee expressio caused by mechaisms other tha chages i the uderlyig DNA sequece, hece the ame epi- (Greek: επίover, above) -geetics. These chages may remai through cell divisios for the remaider of the cell's life ad may also last for multiple geeratios. However, there is o chage i the uderlyig DNA sequece of the orgaism; istead, ogeetic factors cause the orgaism's gees to behave or express themselves differetly. The hypermethylatio of CpG islads i the promoter regios of tumor suppressor gees is a commo hallmark of huma cacer, ad it is associated with iactivatio of these gees. p60trp is particularly iterestig due to its locatio o the X chromosome (Xq23), oe copy of which is radomly iactivated by DNA methylatio i females. 7