in humans implantation usually occurs at

Options

A. morula stage
B. gastrula stage
C. blastocyst stage
D. Zygote Stage

Answer

**Step-by-Step Solution:**

1. **Understanding Implantation**: Implantation is the process where the embryo attaches itself to the wall of the uterus after fertilization.

2. **Stages of Embryonic Development**: After fertilization, the embryo goes through several stages:
- **Zygote Stage**: This is the very first stage, where the fertilized egg is a single cell.
- **Morula Stage**: This stage consists of around 16-60 cells and occurs as the embryo travels down the fallopian tube.
- **Blastocyst Stage**: This is a more advanced stage of development, where the embryo consists of about 100-200 cells. It is during this stage that the embryo is ready to implant into the uterine wall.
- **Gastrula Stage**: This stage occurs after implantation and involves the formation of the three germ layers (ectoderm, mesoderm, and endoderm).

3. **Timing of Implantation**: Implantation typically occurs between 6 to 12 days after fertilization, specifically during the blastocyst stage.

4. **Conclusion**: Therefore, the correct answer to the question of when implantation occurs in humans is during the **blastocyst stage**.

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