Dwi Setyati 2014

Gametogenesis Gamet-gamet sebagai produk akhir meiosis sesungguhnya

belum sepenuhnya berkembang.

Dibutuhkan suatu periode pematangan setelah meiosis sampai menjadi gamet yang siap berfungsi dalam fertilisasi.

Pada tumbuhan, satu atau lebih pembelahan mitosis diperlukan untuk menghasilkan spora-spora yang reproduktif (Mikrospora dan megaspora).

Sedangkan pada hewan, melalui pertumbuhan dan/atau diferensiasi produk-produk meiosis langsung berkembang menjadi gamet.

Proses penghasilan gamet-gamet atau spora-spora matang/dewasa disebut gametogenesis.

Gametogenesis pada hewan jantan disebut spermatogenesis, yaitu terbentuknya sel sperma atau spermazoan (n) dari spermatogonium di dalam gonad jantan (testis).

SPERMATOGENESIS

Proses pembentukan sperma dalam testis

Sel-sel primordial diploid di dalam testismembelah berkali-kali secara mitosismembentuk spermatogonium

Spermatogonium mengalami /diferensiasipertumbuhan membentuk sel spermatositprimer (2n)

Meiosis of each spermatocyte produces 4 haploid spermatids. This process takes over three weeks to complete.

Gambar 1.11. Gametogenesis pada hewan (Sumber: Klug, dkk., 2007 hal. 22)

Sperm

Sperm cells are little more than flagellated nuclei. Each consists of :

a head, which has an acrosome at its tip and

contains a haploid set of chromosomes in a compact, inactive, state.

a midpiece containing mitochondria and a single centriole

a tail

tecn.rutgers.edu/ bio342/sperm_meiosis.htm

OOGENESIS Gametogenesis pada hewan betina disebut oogenesis,

yaitu terbentuknya sel telur atau ovum (n) darioogonium di dalam gonad betina (ovarium).

(Proses pembentukan sel telur di dalam ovarium)

Sel-sel pada ovarium membelah berkali-kali secaramitosis membentuk oogonium

Oogonium mengalami pertumbuhan membentuk seloosit primer (2n)

Sex Organs of the Human Female

Oogenesis

In contrast to males, the initial steps in egg production occur prior to birth. Diploid stem cells called oogonia divide by mitosis to produce more oogonia and primary oocytes.

By the time the fetus is 20 weeks old, the process reaches its peak and all the oocytes that she will ever possess (~4 million of them) have been formed. By the time she is born, 1–2 million of these remain. Each has begun the first steps of the first meiotic division (meiosis I) and then stopped.

No further development occurs until years later when the girl becomes sexually mature. Then the primary oocytes recommence their development, usually one at a time and once a month.

STRUCTURE AND FUNCTION OF THE EGG

During oogenesis, the cytoplasm is unevenly divided during each meiotic division. This results in one egg and three polar bodies.

Here is why. Egg cells must contain enough supplies to synthesize all the products needed by the developing embryo until the embryo implants into the uterine wall. Implantation does not occur until 7-10 days after fertilization. Thus, the unequal division of the cytoplasm ensures the egg has enough supplies for this time period.

:www.agen.ufl.edu/.../ lect/lect_08/lect_08.htm

http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-20/2010.jpg

A damaged cell may undergo apoptosis if it is unable to repair genetic

errors. Apoptosis is a common process throughout life that helps the

body get rid of cells it doesn’t need

Control of cell growth and

division

Control of cell growth and

division

When a cell undergoes apoptosis, white blood cells called

macrophages consume cell debris.

Kanker

Kanker pembunuh terbesar, yaitu kanker paru-paru, membunuh hampir 90% penderitanya, atau hampir 30% dari seluruh kematian akibatkanker. Namun sesungguhnya justru kankerparu-parulah yang paling mudah dicegah. Survey dalam beberapa dekade menunjukkanbahwa satu-satunya penyebab mayoritas kankerparu-paru adalah asap rokok.

http://www.allthingsbeautiful.com/

all_things_beautiful/images/metas

tasizing_cancer.jpg

http://www.tobaccofacts.org/pho

tos/mouth_cancer2.jpg

Gambar Penyakit Kanker (1)

Tampak Depan (Ca.

mamma) Tampak Samping

Ca. ma di Axillary

Tail Spencer Contoh Kanker Payudara

Karsinogen

Zat-zat karsinogen (pemicu kanker) yang terkandung pada rokok adalah:

vinyl chloride

benzo (a) pyrenes

nitroso-nor-nicotine

Satu-satunya zat yang lebih berbahaya daripada asap rokok dalam memicu kanker paru-paru adalah zat-zat radioaktif. Itu pun jika dimakan atau dihisap dalam kadar yang cukup.

Efek Kanker Paru-Paru

Gambar di bawah menunjukkan paru-paru yang dirusak oleh

kanker. Gambar di kanan (diperbesar) menunjukkan alveoli yang

terkena kanker.

http://www.accessexcellence.org/AE/AEPC/NIH/gene13.html

Cancer

usually

arises in

a single

cell

All

cancer

is

genetic

Genetic mutation and cancer development

Cancer results when cells accumulate genetic errors and multiply without control

Cancer results from a disruption of the normal regulation of the cell cycle.

When the cycle proceeds without control, cells can divide without order and accumulate genetic defects that can lead to a cancerous tumor

Cancer results when cells accumulate genetic errors and multiply without control.

Oncogenes normally encourage cell growth; when mutated or overexpressed, they can flood cells with signals to keep on dividing.

Tumor-suppressor genes normally restrain cell growth; when missing or inactivated by a mutation, they allow cells to grow and divide uncontrollably