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Questions and Answers
The human somatic (body) cell contains _____ chromosomes (diploid).
46
The fusion of male and female germ cells (gametes) is called _____ to form a _____ .
How many chromosomes does the human somatic cell contain?
46
What are the sex chromosomes designated as?
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What is the fusion of male and female germ cells called?
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The first phase of development begins at fertilization and spans the first ______ weeks.
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After the first phase, the second phase spans the next ______ weeks of development.
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What is the name of the ball of cells formed after fertilization?
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What is the hollow ball formed after the morula called?
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Which cells form the embryo proper?
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What is the process that initiates differentiation called?
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What are the three primary germ layers involved in embryonic development?
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Study Notes
Germ Cell Formation and Fertilization
- Human somatic cells have 46 chromosomes (diploid), with two designated as sex chromosomes (X and Y).
- Fertilization is the fusion of male and female gametes, resulting in a zygote that begins the formation of a new individual.
- Prenatal development begins with fertilization, lasting about 4 weeks, primarily featuring rapid cell division with initial differentiation.
- The subsequent phase, also 4 weeks, involves significant differentiation of major internal and external structures.
Induction, Competence, and Differentiation
- Induction initiates the differentiation of cells, with inducers providing signals for this process.
- Cells must be competent to respond to induction, which reflects their ability to alter gene expression during development.
- Cell-surface receptors play a critical role in this process, imparting specific capabilities to cells.
Formation of the Three-Layered Embryo
- The fertilized egg quickly divides into a morula, which later forms a blastocyst consisting of a fluid-filled cavity.
- The primary yolk sac cells line the cavity; a smaller cluster of cells becomes the embryoblast.
- Embryoblast cells differentiate into the embryo (development) and trophoblast (placenta formation).
- At around 14 days of gestation, embryoblast cells form a two-layered disk comprising ectoderm (dorsal) and endoderm (ventral).
- The embryonic axis establishes at the head end, where ectoderm meets endoderm at the prochordal plate.
Neurulation and Germ Layer Development
- The process of gastrulation converts the three germ layers into a more complex structure.
- The amniotic cavity floor is formed by mesoderm, which gives rise to the notochord through cellular migration.
- A streak with bulging areas appears, leading to cell migration through it, forming the notochord and mesoderm that separates ectoderm from endoderm.
- The initial 3 weeks of development concludes with significant cell proliferation and migration, establishing major tissues and organs from the three germ layers.
Key Developmental Processes
- Major differentiation events over the next 3-4 weeks include:
- Formation of the neural tube from ectoderm.
- Development of significant organ systems.
- Differentiation in rostrocaudal and lateral planes for comprehensive body structure.
- The nervous system forms as a thickening within the ectoderm, leading to intricate central nervous system development.
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Description
Explore the fundamental concepts of germ cell formation and fertilization in humans. This quiz covers important aspects of somatic cells, chromosomes, and the initial stages of prenatal development. Test your knowledge on the fusion of gametes and the early phase of human development.
