reproduksi sel

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 somatikMEIOSIS → sel seks atau gamet

(spermatozoa dan ovum)

MITOSIS

Interfase Profase Metafase AnafaseTelofase

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 ReproductionInterphase (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-tahapnya 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

CROSSING-OVER: Exchange of chromatid

segments within tetrads to produce new allele combinations

Nonsisters cross over, break, and rejoin

Increases genetic variety

VIEW OF NUCLEUSAND TETRADS

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 IA short interphaselike stage between divisions

PROPHASEII

MEIOSIS

Fase I

Fase II

SEPARATES SISTER CHROMATIDS

PROPHASE II Nuclear membranes disappearNucleoli disappearSpindle fibers formChromatin coils to form chromosomesWhat 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 reappearNucleoli reappearChromosomes uncoil to chromatin Spindle fibers disappearCytokinesis occurs to produce a total of 4

haploid cells (N)

Meiosis : Summary of reduction division

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