Self-study
P1
The first thing any embryo must do before it can develop into an organism is establish early polarity—that is, it must set up a way to distinguish its top from its bottom and its back from its front. ███
Intro topic ·
Embryo polarity
How an embryo develops different “sides”
Contrast species ·
Different species' embryos use different processes to establish polarity
P2
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Example of polarity process ·
Fruit fly
Fruit fly eggs already have all the information needed for polarity even before fertilization; “fertilize-and-go” approach
Consequences ·
of fruit fly polarity process
Tradeoff: eggs take a long time to “set up” ahead of time, but embryo grows very quickly
Contrasting example ·
Nematode
Unlike fruit flies, nematode eggs don’t have all the polarity information they need; sperm also provides information
Elaborate on example ·
Details of process in nematode egg
When sperm enters egg, proteins collect on one side of egg, signaling front/back
Similarity/contrast ·
Nematode-like process used in some vertebrates (frogs) but not others (humans)
Continue contrast ·
Mammal embryos establish polarity much later
But underlying process is unknown
P3
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New contrast ·
between establishing polarity and growing specific body parts
Species differ widely in how they signal polarity in the embryo, yet they’re very similar in how they signal specific body parts to grow
Main point ·
Developmental mechanisms differ between species early on, but are similar later in development
Passage Style
Single position
Spotlight
20.
Which one of the following ████ ██████████ █████████ ███ ████ █████ ██ ███ ████████
a
Species differ more ██ ███ ██████████ ████ █████████ ███ ███████ ███████████ ██ ██ ██████ ████ ████ ██ ██ █████ ███████ ███████ ███████
This isn’t the main point because the author never compares the similarity of mechanisms that determine polarity to overall genetic makeup. The comparison is between mechanisms that determine polarity and those involved in features later in an organism’s developmental process.
b
Embryos determine their █████ ████ █████ ████ ███ ███ ████ ██████ ██ █████████ ████████ █████████ ██ ███████ ███ ████████ ██ ██████ ██ ████ ████████
This isn’t the main point, because the author doesn’t indicate that embryos determine polarity based on methods that differ depending on simplicity or complexity. Although different organisms have different methods, the author never suggests that simple organisms tend to use one method while more complex organisms tend to use a different method.
c
While very similar █████ ████ █████████ ███ █████ █████████ ███████████ ██ ███ ██████████ ███ ███████ ██████████ ██ █████ ███████ █████████ █████ ████████ ████ ████████████ ████ ███ ████████ ██ ███ █████
This best captures the main point. The entirety of P2 is designed to show that the mechanisms for establishing polarity are very different between different organisms. But, the author notes in P3 that the mechanisms for development of later features are very similar.
d
The mechanisms by █████ ███████ █████████ █████ ████████ ██████ █████████ ██ ███████ ███ ███████ ██ █████ ████████ ██ ████████ ███ █████████ ██ ███ █████████ ██ ███ ███ ██ ███ ██████████ ██ ███ ██████
This isn’t the main point, because the inscription of polarity signals in the cytoplasm or p-granules are merely two of the potential polarity mechanisms. The author never suggests that all the mechanisms for polarity in all organisms are based on this cytoplasm vs. p-granule issue.
e
Despite their apparent █████████████ ████ ███████ ██ ████████ ███ █████ ██ █████ █████████ █████████ ████████ ████ ██ ███████████ ███ ████ ███████ ███████████
This is anti-supported. The author indicates in P1 and P2 that the mechanisms for establishing polarity are very different between different organisms.