How do I even comprehend a BB passage like this?

[pretty_positron]

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This is from NS and I don't understand anything here. I don't understand what the charts are supposed to say. I don't understand a variety of the vocabulary.

Can someone please walk me through this and tell me how you would approach this? Just what's going through your mind as you see this and make sense of it.

This was the first passage on a NS FL and I literally spent 30m trying to comprehend what the heck is going on here and then just gave up.

I can see in the bottom graph that B (early culture) to C (late culture) there is more methylation, which means that it's inactive? I see from table 1 that there's some occasions where two sperm fertilize an egg so that's bad. I don't understand at all what table 2 is - I assume eu- means it's okay, so normal (like eu-stress), but I don't understand the difference between Triple X syndrome and Klinefelter's. I don't understand the columns: 0, 1, and 2. I don't understand what A is for in the bottom graph? I don't know how to tell if X inactivation is complete or incomplete even though that's what Table 2 is supposed to tell you.

 

[sapientnarwhal]

Correct me if I am wrong.

Table 2:

The passage frequently mentions the that X-inactivation occurs early in development, specifically the fetal stages. The FISH probe is targeted towards x-inactive specific transcript (XIST). We can infer that active XIST participates in XCI.

For normal females, we expect 1 XIST signal for complete XCI (results are consistent with this hypothesis)
We do not expect any XIST activity in normal males, as the one X remains active (results also confirm this)

Based on these inferences, we continue to XXX and XXY.

For triple X, I believe we would still expect 1 unique signal for complete XCI (alternatively, this could indicate complete XCI of a single X, and no XCI for the remaining 2, but this is seemingly less plausible). This indicates that 2X's are completely inactivated. 2 unique FISH signals indicates a discrepancy in XIST activity, resulting in a discrepancy in relative XCI between the 2 additional X chromosomes.

For Klinefelters, it appears that both X's undergo partial XCI. 1 FISH signal indicates complete XCI.

The absence of a FISH signal for euploid males is the "smoking gun" so to speak.
Though euploid may be an unfamiliar term, it is reasonable to infer this indicates WT (otherwise this table is useless and truly impossible to comprehend).


Figure 1:

A) figure 1 legend title: control and triploid cultures. This consistent with its label as a XaXi diploid female (normal/WT). The only issue I have is the exclusion of a "late culture" control graph. Nonetheless, we expect a 50:50 ratio of hypo:hypermethylation in the late culture.

The key to understanding the significance of Figure 1 is the last statement of the passage, "ratio of hypo:hypermethylation in triploids agreed with expected ratios of Xa:Xi".

Because graph C depicts a 50:50 ratio, I suspected that inactivation produces a 50:50 ratio of active:inactive X chromosomes. So incomplete XCI for XXX is more likely to occur than complete XCI, which is evident in the relative percentage of complete to incomplete XCI for XXX (table 2).

Also a greater percentage of XXY showed complete XCI (table 2), which is more conducive to obtaining a 50:50 ratio active:inactive X's.


This was undeniably a difficult passage, and I got 1 or 2 wrong. My only advice is to identify the connection between the figures/data and the study hypothesis and/or conclusion.

 

[sapientnarwhal]

@pretty_positron

Is this explanation correct? I forgot which test this is from, so this is my interpretation based on the given info

 

[pretty_positron]

@pretty_positron

Is this explanation correct? I forgot which test this is from, so this is my interpretation based on the given info

Sorry I haven't had a chance to take a look at it yet, but thank you SO much for your response. I really need help in this type of stuff.

What goes through your mind, personally, when you come across a passage like this? How do you process it? Personally. Do you look at the answers first and see if you can figure out an answer? Do you skip it and come back to it later. This was the first passage in this section so it psyched me out.

I'll read what you wrote and give you a full response, but again, thanks SO much. I really really need help with this stuff.