{FREE} Short Notes on Gametogenesis, Fertilization and Early Development - Download PDF!

By Renuka Miglani|Updated : October 19th, 2021

Are you looking for some short and reliable notes during your CSIR-NET preparations? Then, you have come to a perfect place!

Candidates preparing for their CSIR NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point, We at Byjus Exam Prep come up with short notes on Gametogenesis, Fertilization and Early Developmentwhich comes under the Developmental Biology section of the Life Science syllabus. 

Our experienced subject-matter experts have meticulously designed this set of short notes to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them learn and for their future. So, here we are offering the best study notes that are reliable and can be used by the students during CSIR-NET 2021 preparation.

Are you looking for some short and reliable notes during your CSIR-NET preparations? Then, you have come to a perfect place!

Candidates preparing for their CSIR NET exam might need to get some short study notes and strategies to apply while preparing for the key exam of their life. At this point, We at Byjus Exam Prep come up with short notes on Gametogenesis, Fertilization and Early Development, which comes under the Developmental Biology section of the Life Science syllabus. 

Our experienced subject-matter experts have meticulously designed this set of short notes to give you the most standard set of study materials to be focused upon. In this cut-throat competitive world, students need to prepare themselves with the best study materials to help them learn and for their future. So, here we are offering the best study notes that are reliable and can be used by the students during CSIR-NET 2021 preparation.

Study Notes on Gametogenesis, Fertilization and Early Development 

Gametogenesis is the production of sperm (spermatogenesis) and egg(oogenesis), which takes place through the process of meiosis.

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SPERMATOGENESIS

  • Spermatogenesis occurs in seminiferous tubules, in this tubule are diploid, undifferentiated cells, called spermatogonia, go through mitosis and increase number.
  • Meiosis begins with a cell called primary spermatocyte. At the end of the first meiotic division, a haploid cell is produced called a secondary spermatocyte.
  • This haploid cell must go through another meiotic cell division. The cell produced at the end of meiosis is called a spermatid.
  • When it reaches the lumen of the tubule and grows a flagellum it is called sperm cell. Four sperm result from each primary spermatocyte that goes through meiosis.
  • Spermatogonia cells are deposited during gestation and are present at birth through the beginning of adolescence, but in an inactivation of these cells and the production of visible sperm. This continues into old age.
  • Spermatozoa are later called sperms.

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OOGENESIS

  • Oogenesis occurs in the ovaries.
  • Oogenesis starts with a germ cell, called an oogonium, but this cell undergoes mitosis to increase the number, eventually resulting in up to one to two million cells in embryo.
  • The cell’s starting meiosis is called primary oocyte. This cell will begin the first meiotic division but be arrested in its progress in the first prophase stage. (Prophase 1)
  • At the time of birth, all future eggs are in prophase stage.
  • At adolescence, another pituitary hormone causes the development of a number of follicles in an ovary. This results in the primary oocyte finishing the first meiotic division.
  • The cell divides unequally, with most of the cellular and organelles going to one cell, called a secondary oocyte.
  • Only one set of chromosomes and a small amount of cytoplasm going to another cell. This second cell is called polar body.
  • A secondary meiotic arrest occurs, this time at the metaphase 11 stage.
  • At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis 11, completing meiosis, producing a second polar body and fertilized egg containing all 46 chromosomes of human being, half of them coming from sperm.
  • Arrest is due to lack of sufficient cell cycle proteins to allow meiotic progression.

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FERTILIZATION

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EVENTS OF FERTILIZATION

  1. CAPACITATION
  2. CHEMOATTRACTION
  3. BINDING OF SPERM TO CUMULUS
  4. ACROSOMAL REACTION
  5. BINDING OF SPERM TO ZONA PELLUCIDA
  6. FUSION OF SPERM PLASMA MEMBRANE TO EGG PLASMA MEMBRANE

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OCCURS IN - AMPILLA OF OVIDUCT

Important Events Occurs in Capacitation

  • Final Maturation Occurs in Capacitation.
  • Sperm maturation occurs.
  • Proteins and carbohydrates are lost on sperm.
  • Removal of cholesterol. (as shown above in diagram)
  • Efflux of K+ from sperm head
  • Calcium permeability increases inside sperm.

CHEMO-ATTRACTION

Thermotaxis – sperm sense heat

There is thermal gradient of 2-degree c between the is thymus of oviduct and the warmer ampullary region. This ability to sense temperature difference and preferentially swim from cooler to warmer sites(thermotaxis) is found only in capacitated sperm.

Chemotaxis- progesterone (e.g., rabbit, mouse) progesterone has been shown to bind to receptor that activates Ca2+ channels in cell membrane of the sperm tail, leading to sperm hyperactivity.

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BINDING OF SPERM TO ZONA PELLUCIDA

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The human zona pellucida has four major glycoproteins- ZPQ, ZP2, ZP3, AND ZP4. The binding of sperm to the zona pellucida occurs. (as shown in diagram above)

SPECIES INTERACTION

Sperm recognize ZP2 Protein on Zona Pellucida. In gain of function experiment, ZP2 was shown to be critical for human sperm-egg.

GAMETE FUSION

The acrosome reaction in addition to expelling the enzymatic contents of the acrosome also exposes the inner acrosomal membrane to outside. The junction between this inner acrosomal membrane and the sperm cell membrane is called the equatorial region.

IZUMO PROTEIN

It is originally found in the membrane of the acrosomal granules. However, after the acrosome reaction, Izumo redistributes along on the surface of acrosome reacted sperm, where it is found primarily in the equatorial section, where mammalian sperm-egg binding takes place.

STAGES OF EARLY DEVELOPMENT IN MAMMALS

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Prior to fertilization the mammalian oocyte, wrapped in cumulus cells, is released from the ovary, and swept by the fimbriae into the oviduct. Fertilization occurs in the ampulla of oviduct, a region closes to ovary, mitosis is completed after sperm entry, and the first cleavage begins about a day later. The cilia in the oviduct push the embryo toward the uterus and, first cleavages occur along this journey.

  1. Zygote
  2. 2 celled stage -zygote divide into 2- cells
  3. Further 2 celled stages divide to form 4- celled stage.
  4. After 4 celled comes 8- celled stage
  5. Morula- After 8-celled stage further division occurs and a ball of cells form called Morula.
  6. Blastula- After morula stage comes blastula stage in which ball of cells divide into trophoblast outer group of cells and Inner cell mass (ICM).
  7. Finally, this get implanted into mother’s womb.

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