ساينس الصف الثالث الاعدادي – الفصل الدراسي الاول ساينس تالتة اعدادي – ترم اول In This part we will study : Meiosis Meiosis occurs in living organisms that reproduce by gametes. Occurrence : * In humans and animals, Its important this division occurs in the testis to produce the male gametes ( sperms) and in the ovary to form t he female gametes ( ova). * in flowering plants this division occurs in the anther to produce the pollen grains and in the flower ovary to form an egg. Importance :production of male gametes and females gametes to complete the sexual reproduction. Phases of meiosis: 1 – First meiotic division 2 – Second meiotic division. First meiotic division Prophase 1 , Metaphase 1 , Anaphase 1 and Telophase 1 The crossing over phenomenon At the end of prophase I, some parts of the two inner chromatids of each tetrad are exchanged to produce new genetic arrangements. This process is called the crossing over phenomenon. Crossing over phenomenon It is a phenomenon that takes place at the end of prophase 1 and in which some parts of the two inner chromatids of each tetrad are exchanged to produce new genetic arrangements. لمتابعة مستر احمد الباشا وكل ما يخص الساينس : جروب الفيس بوك http://bit.ly/2Of1mcN صفحة الفيس بوك http://bit.ly/2Gq5xMo بالتوفيق مستر احمد الباشا