LSAT 121, Section 3, RC Passage 4, Polarity

RC Passage 4 Explanation

PASSAGE TEXT: The first thing any embryo must do before it can develop into an …

Paragraph Summaries

1. An embryo first needs to establish polarity, meaning it needs to know its basic orientation (front/back and top/bottom). The way embryos do this differs greatly across species, even though later development (like forming limbs and organs) is more similar.
2. Different animals establish polarity in different ways. Fruit flies have positional information already built into the egg before fertilization, while nematodes rely on the sperm’s entry point and the movement of p-granules. Mammals appear to develop polarity later, but scientists are still unsure how this happens.
3. Once polarity is established, embryos across species use many of the same genes to build body parts. So early development is very different between species, but later development becomes surprisingly similar.

Analysis

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