Question from TPRH Workbook

[yanks26dmb]

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Passage 46, question 4..

Related text:

Experiment 4

Non-identical twin cattle that shared a placenta in utero were found to accept skin grafts from one another. Non-identical twins that had separate placentas in utero rejected skin grats from one another.

Question:

Experiment 4 supports the hypothesis that immunological self-tolerance is:

A: a genetic phenomenon
B: passed from mother to offspring
C: a characteristic acquired during development
D: facilitated by reduced blood flow in a shared placenta.

Correct answer is C, but I don't see how the experiment shows this. On the contrary it would appear that reduced blood flow would be the reason given the two scenarios listed. If C were correct and self tolerance is a characteristic acquired during development (a rather general statement) then why wouldn't the two non-identical twins with separate placentas have acquired self-tolerance? They too underwent development...

 

[orangetea]

hmm I see where you are coming from but I think this question could be answered using POE.

A. It's not a genetic phenomenon because it doesn't look like one set of twins has a mutation, extra genetic material, etc. than the other set.
B. It can't be caused by mother to offspring because in both sets they are receiving mother's blood and genetic material.
C- Yes!!


I think it's D you are confused about? Well this is quoted from a pamphlet about twins

"Although in some monochoronic pregnancies the placenta is divided equally between the
twins, in approximately 40% of cases one baby has a disproportionately smaller share of
placenta which may result in that baby not growing as well. This is known as intrauterine
growth restriction (IUGR). "

C is the correct answer because in the case of identical twins ONE egg is split into two and fertilized by ONE sperm so it would make sense that they can accept skin grafts from one another given that they are essentially formed from the same egg. Whereas in the case of the fraternal twins TWO eggs are fertilized by TWO sperm and so it would make sense that they do not accept skin grafts from one another. 🙂

#twinning

 

[DrknoSDN]

C is the correct answer because in the case of identical twins ONE egg is split into two and fertilized by ONE sperm so it would make sense that they can accept skin grafts from one another given that they are essentially formed from the same egg. Whereas in the case of the fraternal twins TWO eggs are fertilized by ONE sperm and so it would make sense that they do not accept skin grafts from one another. 🙂

Whoa, whoa,, slow down. Fraternal twins are Two eggs and TWO sperm. The sperm does not enter one egg and then leave to go implant a second egg. That would just be greedy. 😀

 

[orangetea]

Whoa, whoa,, slow down. Fraternal twins are Two eggs and TWO sperm. The sperm does not enter one egg and then leave to go implant a second egg. That would just be greedy. 😀

Thank you for that!! I was copy and pasting like crazy but major fail on my part 🙂