As in the development of spores of yeast, a single diploid cell in the ovary of a female fly gives rise to a number of haploid cells. In Drosophila the precursor cell undergoes four divisions to yield sixteen cells (Fig. 1). These are not separated, but retain communication with one another via cytoplasmic bridges. Eventually, one of the two cells with four connections to other cells moves to the end of the group and begins the development process of generating an egg. The fifteen connected cells assist the process and are called nurse cells. While it is developing, the future egg cell is called an oocyte. The nurse cells absorb nutrients from the surrounding fluid and synthesize rRNA, mRNA, and other components. Additionally, maternal diploid cells also influence the developing oocyte. (Fig. 2). These are called the follicle cells, and they surround the nurse cells and developing oocyte. Partway through the oogenesis pathway, the nurse cells empty their contents into the developing oocyte. When the maturation process is complete, the synthetic activities in the follicle cells almost ceases.

Fig1. Creation of nurse and egg cells from a precursor stem cell in the ovary of a Drosophila. The first division of the stem cell yields one cell which remains stem cell type and a daughter cell that will yield nurse and egg cells. Four additional divisions yield a network of interconnected cells.

Fig2. Later stage of egg development showing an egg cell plus nurse cells surrounded by follicle cells. Although each cell possesses a nucleus and 16 are present, not all nuclei are in the plane of the cross section. The future egg cell is at the far right. At a still later stage of development the egg is enlarging and the nurse cells are found at the left.

Upon fertilization, DNA synthesis begins at a high rate in the egg. Many replication origins are utilized per chromosome so that a chromosome doubling can take as little as ten minutes. The original diploid chromosome doubles ten times, then a few nuclei migrate to the posterior pole of the egg where they ultimately become the germ line cells. The remainder of the nuclei migrate to the surface of the egg and divide four more times, yielding a total of about 4,000 nuclei. At this point nuclear membranes and cell walls develop, creating isolated cells. This stage consists of a single layer of cells and is called a blastula.

Up to the time of wall formation, the nuclei are not committed to any developmental fate, for they can be moved to different locations without altering the development of the embryo. After the walls form, the cells are partially committed, and relocating them interferes with normal development. About six hours after fertilization the embryo develops about 14 distinguishable segments. Six of these ultimately fuse to yield the head, three become the thorax, and about eight develop into the abdomen. By 24 hours after fertilization the larva is fully developed.

اخر الاخبار

اخبار العتبة العباسية المقدسة

قسم الشؤون الفكرية يباشر أعماله الفنية الخاصة بالموكب الثقافي العام ومسابقة مراقي المجتبى

العتبة العباسية المقدسة تعقد اجتماعًا تنسيقيًّا لمناقشة الاستعدادات الخاصّة بزيارة الأربعين

العتبة العباسية المقدسة تكشف تفاصيل مشروع صحن وسرداب أبي الفضل العباس (عليه السلام)

قسم الإعلام يصدر العدد 513 من مجلة صدى الروضتين

المزيد

الآخبار الصحية

دراسة علمية تكشف مفاجأة حول الأسباب الحقيقية للسمنة

دراسة: الأطباء يتجاهلون "سببا شائعا" لارتفاع ضغط الدم

نظامك الغذائي غني بالبروتين؟.. احذر هذه الآثار الجانبية

لا تتجاهلها.. أعراض تنذرك بأنك مهدد بالإصابة بالسكري

المزيد

الآخبار التكنلوجية

ISOFIX: معيار الأمان الذهبي لمقاعد الأطفال في السيارات

هل المحرك الأكبر دائمًا الأفضل للسيارة؟

اختبارات ناجحة لمحرك "VK-800" الروسي وتطويره لطائرة بايكال الخفيفة

رئيس إنفيديا: الذكاء الاصطناعي الصيني "محفز للتقدم العالمي"

المزيد

مواضيع ذات صلة

Chromosome Mapping

Physical and Genetic Maps of Chromosomes

Fate Mapping and Study of Tissue-Specific Gene Expression

Isolating Mutations in Muscle or Nerve in Drosophila

Elements of Drosophila Genetics

Elements of Yeast Genetics

Principles of Bacterial Sex

Crossover

Mapping with Generalized Transducing Phage

Genetic Selections

Growing Cells for Genetics Experiments

Genetic Systems