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Questions and Answers
What is the primary role of fertilization cleavage in early development?
What is the primary role of fertilization cleavage in early development?
Which layer of the blastocyst is responsible for forming the placenta?
Which layer of the blastocyst is responsible for forming the placenta?
What occurs during the apposition phase of implantation?
What occurs during the apposition phase of implantation?
Which hormone is secreted by the syncytiotrophoblast during implantation?
Which hormone is secreted by the syncytiotrophoblast during implantation?
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What characterizes the structure of the blastocyst at 4-5 days post-fertilization?
What characterizes the structure of the blastocyst at 4-5 days post-fertilization?
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What is the primary outcome of fertilisation?
What is the primary outcome of fertilisation?
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During which stage is the primary oocyte arrested in oogenesis?
During which stage is the primary oocyte arrested in oogenesis?
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What is the term for the division of the prenatal period into 3 segments?
What is the term for the division of the prenatal period into 3 segments?
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What type of cell results from the transformation of spermatids during spermiogenesis?
What type of cell results from the transformation of spermatids during spermiogenesis?
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Which of the following describes the acrosomal reaction?
Which of the following describes the acrosomal reaction?
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What is a teratogen?
What is a teratogen?
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At what stage does cleavage begin after fertilisation?
At what stage does cleavage begin after fertilisation?
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What happens to the secondary oocyte if fertilisation does not occur?
What happens to the secondary oocyte if fertilisation does not occur?
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Study Notes
Gametes and Fertilization
- Gamete: Specialized haploid (n) reproductive cell
- Sperm cells: Male gamete
- Egg cell/ovum: Female gamete
- Embryo: Developing human being (weeks 1-8)
- Fetus: Developing human being (weeks 9-36)
- Trimester: 3-month division of the 9-month prenatal period
- Teratogen: Substance causing developmental anomaly (e.g., alcohol, thalidomide, virus, lead, radiation)
- Mutagen: Agent causing genetic mutations (e.g., aflatoxins, HPV)
Gametogenesis
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Spermatogenesis: Sperm formation in testes
- Meiosis I: Primary spermatocyte (2n) → 2 haploid cells
- Meiosis II: Secondary spermatocytes → 4 haploid cells
- Spermiogenesis: Spermatids mature into spermatozoa
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Oogenesis: Ovum/egg formation in ovary
- Begins in fetal period
- Oogonium → primary oocyte
- Primary oocyte arrests in prophase I (meiosis I).
- Primary oocyte matures into secondary oocyte at puberty but arrests at metaphase II.
- Secondary oocyte matures into ovum only with fertilization.
Fertilization
- Fertilization: Sperm and ovum unite to form a zygote (in fallopian tube's ampulla)
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Stages of Fertilization:
- Gamete transport to uterine ampulla
- Sperm capacitation: Final sperm preparation for ovum penetration
- Acrosomal reaction (sperm release hyaluronidase to penetrate ovum)
- Cortical/zona pellucida reaction (ovum prevents polyspermy)
- Syngamy (fusion of pronuclei)
Outcomes of Fertilization
- Diploid number restored (2n): in zygote
- Sex determination: Sperm (X or Y chromosome)
- Cleavage initiation: Rapid cell division of zygote
- Genetic diversity: Combination of parental genetic material
Cleavage
- Zygote: Single-celled stage
- Blastomere formation: 2-8 blastomeres
- Morula: 16-23 blastomeres
- Blastula: Hollow ball of cells
- Blastocyst: Blastula with cavity
- Importance of Cleavage: Establishes multicellularity, decreases cell size, and prepares for implantation/gastrulation
Blastocyst Structure
- Formation: 4-5 days post-fertilization
- Layers: Trophoblast (outer) and embryoblast (inner)
- Zona pellucida: Surrounds both layers
- Implantation: Trophoblast at embryonic pole
- Embryo development: Embryoblast → embryo
- Placenta formation: Trophoblast → placenta
Implantation
- Apposition: Blastocyst approaches uterine wall (posterior/anterior)
- Trophoblast differentiation: Cytotrophoblast and syncytiotrophoblast
- Endometrial penetration: Syncytiotrophoblast penetrates endometrium
- HCG secretion: Syncytiotrophoblast secrets human chorionic gonadotropin
- Corpus luteum: Maintains pregnancy (secretes progesterone)
- Layers of trophoblast: Cytotrophoblast faces embryoblast; syncytiotrophoblast faces away from embryoblast
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Description
Test your knowledge on the process of gametogenesis, fertilization, and the different stages of human development. This quiz covers key concepts including sperm and egg formation, as well as the role of teratogens and mutagens in development. Perfect for biology students studying reproductive processes.
