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Questions and Answers
What is formed when the male and female pronuclei fuse?
What is formed when the male and female pronuclei fuse?
- Embryo
- Zygote (correct)
- Blastocyst
- Morula
How many chromosomes are present in the zygote at fertilization?
How many chromosomes are present in the zygote at fertilization?
- 64
- 46 (correct)
- 23
- 92
What occurs during the cleavage stage of embryogenesis?
What occurs during the cleavage stage of embryogenesis?
- Blastomeres form. (correct)
- Differentiation of cells starts.
- Growth of the zygote occurs.
- Formation of the placenta begins.
During which stage does the embryo organize into a multilayered structure?
During which stage does the embryo organize into a multilayered structure?
What is the primary result of fertilization, apart from the formation of the zygote?
What is the primary result of fertilization, apart from the formation of the zygote?
What happens to the tail of the sperm during the fertilization process?
What happens to the tail of the sperm during the fertilization process?
What is the solid ball of cells formed at the 32-cell stage called?
What is the solid ball of cells formed at the 32-cell stage called?
What process follows the initial fusion of pronuclei in embryogenesis?
What process follows the initial fusion of pronuclei in embryogenesis?
What is the result of the fusion of a sperm and an oocyte?
What is the result of the fusion of a sperm and an oocyte?
During which phase of fertilization does the zona reaction occur?
During which phase of fertilization does the zona reaction occur?
What is the primary role of hyaluronidase during fertilization?
What is the primary role of hyaluronidase during fertilization?
At what point is fertilization considered to have completed embryogenesis?
At what point is fertilization considered to have completed embryogenesis?
What is the chromosomal implication of the zygote formation?
What is the chromosomal implication of the zygote formation?
Which enzyme is specifically involved in lysis of the zona pellucida during fertilization?
Which enzyme is specifically involved in lysis of the zona pellucida during fertilization?
Which cell division completes when the sperm enters the secondary oocyte?
Which cell division completes when the sperm enters the secondary oocyte?
Which part of the female reproductive system is the site of fertilization?
Which part of the female reproductive system is the site of fertilization?
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Study Notes
Fertilization
- Fertilization is the fusion of a sperm and an egg (oocyte)
- Each gamete is haploid (contains half the genetic material)
- Fusion creates a diploid zygote (contains the full genetic material needed for a human)
- Occurs in the ampulla of the uterine tube
- Lasts about 24 hours
Phases of Fertilization
- Passage through corona radiata: Sperm uses hyaluronidase to break down the corona radiata layer, tail movement also helps
- Penetration of zona pellucida: Sperm releases enzymes (acrosin and neuraminidase) to break down the zona pellucida, creating a pathway. Zona reaction occurs to prevent further sperm entry
- Fusion of oocyte and sperm cell membrane: Plasma membranes fuse and break down at the fusion point, sperm nucleus enters oocyte cytoplasm
- Completion of second meiotic division: Secondary oocyte completes meiosis, forming a mature oocyte (ovum) and a second polar body. The oocyte nucleus is now called the female pronucleus, containing 23 chromosomes
- Formation of the male pronucleus: Sperm nucleus enlarges within the oocyte cytoplasm, forming the male pronucleus. The tail degenerates.
- Male and female pronuclei contact: Lose their nuclear membranes and fuse, forming a zygote. Each pronucleus has 23 chromosomes, the zygote now has 46 chromosomes.
- Mitosis: The zygote undergoes mitosis, dividing into two daughter cells. This marks the 2-cell stage.
Results of Fertilization
- Restores the diploid number of chromosomes
- Determines the sex of the embryo
- Initiates cleavage
Embryogenesis
- Embryo development spans from the 2-cell stage until week 8 of gestation
- Cleavage: Zygote undergoes rapid mitotic divisions without increasing overall size, producing blastomeres.
- Morula: 32-cell stage. Contains an inner cell mass (future embryo and fetus) and an outer cell mass (trophoblast, future placenta)
- Growth: Blastula reorganizes into a multilayered gastrula with three germ cell layers: ectoderm, endoderm, and mesoderm
- Differentiation: Unspecialized embryonic cells change into specialized cells, tissues, and organs.
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