REPRODUKSI SEL

Reproduksi protista berbeda dengan sel hewan lainnya Jamur → spora Tanaman → biji Hewan → telur Protista → sel tunggal Sel anak → mempunyai membran, sitoplasma dan inti Inti mengandung DNA yang identik

Salah satu protista adalah amoeba Amoebas → sangat tipis, membran sel fleksibel Bergerak dengan menjulurkan sitoplasma keluar membran dan membentuk pseudopods ("false feet") Di dalam sel terdapat ruang sbg organ percernaan

REPRODUKSI SEL

 MITOSIS → sel somatik  MEIOSIS → sel seks atau gamet (spermatozoa dan ovum)

MITOSIS

Interfase Profase Metafase Anafase Telofase 1. Terjadi sintesis protein; kromatin dan inti nampak jelas; replikasi DNA 2.

Kromatin tebal → kromosom; membran inti melebur; sentriol bergerak pada sisi yang berlawanan dan serabut spindel mulai terbentuk 3. Kromosom yang dihubungkan spindel ada di tengah 4. Kromosom memisah menuju ke kutub yang berlawanan 5. Kromosom kembali berbentuk kromatin; speindel melebur; membran inti nampak; sentriol replikasi; terbentuk membran sel baru

Cell Reproduction

Interphase (before Mitosis) Early Prophase Prophase Late Prophase Transition to Metaphase Metaphase Anaphase Telophase

MEIOSIS :

• • Terdiri dari 2 fase : Meiosis I : merupakan pembelahan yang memisahkan 2 kromosom homolog (kromatid), terjadi reduksi kromosom Meiosis II : merupakan pemisahan kromatid melalui pembelahan sentromer.

Hasilnya : sel diploid menghasilkan 4 sel anakan yang haploid Tahap-tahap nya sbb :

PROPHASE I

 SYNAPSIS - the pairing and bonding together of homologous chromosomes to form tetrads  Homologous chromosomes consist of one maternal and one paternal chromosome

PROPHASE I

VIEW OF NUCLEUS AND TETRADS CROSSING-OVER :  Exchange of chromatid segments within tetrads to produce new allele combinations  Nonsisters cross over, break, and rejoin  Increases genetic variety

CROSSING -OVER

 Notice the exchange of segments that has happened in two places on the larger homologous pair  This is crossing over

METAPHASE I

 Tetrads line up in the middle of the cell in a straight line at equator  Spindle fibers attach to only 1 kinetochore of each centromere

ANAPHASE I

 Tetrads are separated as homologous chromosomes are pulled to opposite poles of the cell  (Remember: the chromosomes are still actually sister chromatids)

TELOPHASE I

 Cytokinesis may occur and two HAPLOID cells containing sister chromatids are produced  A brief period of interkinesis occurs

INTERKINESIS

TELOPHASE I A short interphase like stage between divisions II

MEIOSIS

SEPARATES SISTER CHROMATIDS

Fase I Fase II

PROPHASE II

 Nuclear membranes disappear  Nucleoli disappear  Spindle fibers form  Chromatin coils to form chromosomes  What does this remind you of ?

 Prophase II is basically the same as mitosis prophase x 2

METAPHASE II

 In metaphase II the two cells line up their chromosomes in the middle of the cell in a straight line at equator  Again this is the same as mitosis metaphase - only two cells are doing it  Each cell is doing it with only 1 chromosome of each kind, not pairs

ANAPHASE II

 During this phase the centromeres of the chromosomes in the two cells divide and sister chromatids move to opposite poles of the cells  Very mitosis-like again

TELOPHASE II

 Final act of meiosis  Nuclear membranes reappear  Nucleoli reappear  Chromosomes uncoil to chromatin  Spindle fibers disappear  Cytokinesis occurs to produce a total of 4 haploid cells (N)

Meiosis : Summary of reduction division

Phases of spermatogenesis (i.e., meiosis in males)