BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Population Bottleneck

This topic has expert replies
Post new topic Locked
Previous Topic Next Topic
User avatar
Master | Next Rank: 500 Posts
Posts: 377
Joined: Wed Sep 14, 2011 10:45 am
Thanked: 10 times
Followed by:1 members

Population Bottleneck

by imskpwr » Fri Jun 15, 2012 9:42 pm
Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"-at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

A. at some time in the past our ancestors suffered an event, greatly reducing their numbers
B.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C.that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E.some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,

[spoiler]Source: OG13 Q97[/spoiler]

Please explain the usage of "dash" here.
I think that "at some time in .....an event" defines "population bottleneck".

"greatly reducing.......variation." is modifying which clause and why?. Because of "dash", I don't know that on which "subject" this "ing" modifier is acting.

OA is B.
Top
Source: — Sentence Correction |
Junior | Next Rank: 30 Posts
Posts: 21
Joined: Mon Mar 08, 2010 4:19 am

by GMAT_2010_2707 » Fri Jun 15, 2012 10:03 pm
Dash (-) can be used just in the same way as Comma is used. It is a very flexible punctuation.
"at some time in the past our ancestors suffered an event" act as a non-essential modifier.
In option "B" that refers back to population bottleneck - which is correct.
In option "A", reducing refers back to the entire clause which is not required here.
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 377
Joined: Wed Sep 14, 2011 10:45 am
Thanked: 10 times
Followed by:1 members

by imskpwr » Fri Jun 15, 2012 11:23 pm
GMAT_2010_2707 wrote:Dash (-) can be used just in the same way as Comma is used. It is a very flexible punctuation.
"at some time in the past our ancestors suffered an event" act as a non-essential modifier.
In option "B" that refers back to population bottleneck - which is correct.
In option "A", reducing refers back to the entire clause which is not required here.
I don't think that we can replace a "dash" with "," here.
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sat Jun 16, 2012 4:03 am
imskpwr wrote:Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"-at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

A. at some time in the past our ancestors suffered an event, greatly reducing their numbers
B.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C.that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E.some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,

[spoiler]Source: OG13 Q97[/spoiler]

Please explain the usage of "dash" here.
I think that "at some time in .....an event" defines "population bottleneck".

"greatly reducing.......variation." is modifying which clause and why?. Because of "dash", I don't know that on which "subject" this "ing" modifier is acting.

OA is B.
COMMA + VERBing should refer to the SUBJECT of the preceding clause. In A, reducing seems to refer to our ancestors, implying that OUR ANCESTORS were greatly reducing their numbers. The intended meaning here is that an EVENT greatly reduced their numbers. Eliminate A.

So that (in C) and so as (in E) imply PURPOSE. The result is a strange meaning: that our ancestors suffered for the PURPOSE of reducing their numbers. Not the intended meaning. Eliminate C and E.

In D, which seems to refer to an event, implying that our ancestors' numbers were reduced FROM an event -- a nonsensical meaning. Eliminate D.

The correct answer is B.

Like a colon, a dash at the end of a sentence serves to introduce information that explains or defines the preceding clause. The clause that PRECEDES the dash must be INDEPENDENT, but what follows the dash can take on different forms. In the OA, what follows the dash (that our ancestors suffered an event) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 377
Joined: Wed Sep 14, 2011 10:45 am
Thanked: 10 times
Followed by:1 members

by imskpwr » Sat Jun 16, 2012 9:06 pm
GMATGuruNY wrote:
imskpwr wrote:Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"-at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

A. at some time in the past our ancestors suffered an event, greatly reducing their numbers
B.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C.that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E.some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,

[spoiler]Source: OG13 Q97[/spoiler]

Please explain the usage of "dash" here.
I think that "at some time in .....an event" defines "population bottleneck".

"greatly reducing.......variation." is modifying which clause and why?. Because of "dash", I don't know that on which "subject" this "ing" modifier is acting.

OA is B.
COMMA + VERBing should refer to the SUBJECT of the preceding clause. In A, reducing seems to refer to our ancestors, implying that OUR ANCESTORS were greatly reducing their numbers. The intended meaning here is that an EVENT greatly reduced their numbers. Eliminate A.

So that (in C) and so as (in E) imply PURPOSE. The result is a strange meaning: that our ancestors suffered for the PURPOSE of reducing their numbers. Not the intended meaning. Eliminate C and E.

In D, which seems to refer to an event, implying that our ancestors' numbers were reduced FROM an event -- a nonsensical meaning. Eliminate D.

The correct answer is B.

Like a colon, a dash at the end of a sentence serves to introduce information that explains or defines the preceding clause. The clause that PRECEDES the dash must be INDEPENDENT, but what follows the dash can take on different forms. In the OA, what follows the dash (that our ancestors suffered an event) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.
First of all, thanks Mitch for pointing the exact usage of Dash here.
I had no idea that dash was used to define a whole clause here. i thought that it was "population bottleneck",which was defined using dash.

other issue was with "ing" modifier:

1. Some anthropologists believe that...
2. the genetic homogeneity evident in the world's people is the result of a "population bottleneck".
3. at some time in the past our ancestors suffered an event.

there are three clauses.

1 is an Independent Clauses.
2 is also an independent NOUN clause defining "Believe".
3 is // to 2. But, is it dependent clause/independent clause/simply an added information?

Now, "Comma + ing form" should refer to the "subject" of the preceding clause.
so here why is it 2 only?
can it be 1 or 2, as both are preceding clauses?
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sun Jun 17, 2012 3:15 am
imskpwr wrote:
GMATGuruNY wrote:
imskpwr wrote:Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"-at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

A. at some time in the past our ancestors suffered an event, greatly reducing their numbers
B.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C.that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E.some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,

[spoiler]Source: OG13 Q97[/spoiler]

Please explain the usage of "dash" here.
I think that "at some time in .....an event" defines "population bottleneck".

"greatly reducing.......variation." is modifying which clause and why?. Because of "dash", I don't know that on which "subject" this "ing" modifier is acting.

OA is B.
COMMA + VERBing should refer to the SUBJECT of the preceding clause. In A, reducing seems to refer to our ancestors, implying that OUR ANCESTORS were greatly reducing their numbers. The intended meaning here is that an EVENT greatly reduced their numbers. Eliminate A.

So that (in C) and so as (in E) imply PURPOSE. The result is a strange meaning: that our ancestors suffered for the PURPOSE of reducing their numbers. Not the intended meaning. Eliminate C and E.

In D, which seems to refer to an event, implying that our ancestors' numbers were reduced FROM an event -- a nonsensical meaning. Eliminate D.

The correct answer is B.

Like a colon, a dash at the end of a sentence serves to introduce information that explains or defines the preceding clause. The clause that PRECEDES the dash must be INDEPENDENT, but what follows the dash can take on different forms. In the OA, what follows the dash (that our ancestors suffered an event) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.
First of all, thanks Mitch for pointing the exact usage of Dash here.
I had no idea that dash was used to define a whole clause here. i thought that it was "population bottleneck",which was defined using dash.

other issue was with "ing" modifier:

1. Some anthropologists believe that...
2. the genetic homogeneity evident in the world's people is the result of a "population bottleneck".
3. at some time in the past our ancestors suffered an event.

there are three clauses.

1 is an Independent Clauses.
2 is also an independent NOUN clause defining "Believe".
3 is // to 2. But, is it dependent clause/independent clause/simply an added information?

Now, "Comma + ing form" should refer to the "subject" of the preceding clause.
so here why is it 2 only?
can it be 1 or 2, as both are preceding clauses?
COMMA + VERBing should modify the NEAREST preceding subject and verb.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 377
Joined: Wed Sep 14, 2011 10:45 am
Thanked: 10 times
Followed by:1 members

by imskpwr » Sun Jun 17, 2012 4:39 am
Thanks!
You rock!
As always,your explanations are to the point.
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 206
Joined: Sun Jun 24, 2012 5:44 pm
Thanked: 5 times
Followed by:3 members

by [email protected] » Fri Oct 14, 2016 12:51 pm
GMATGuruNY wrote:
imskpwr wrote:Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"-at some time in the past our ancestors suffered an event, greatly reducing their numbers and thus our genetic variation.

A. at some time in the past our ancestors suffered an event, greatly reducing their numbers
B.that at some time in the past our ancestors suffered an event that greatly reduced their numbers
C.that some time in the past our ancestors suffered an event so that their numbers were greatly reduced,
D. some time in the past our ancestors suffered an event from which their numbers were greatly reduced
E.some time in the past, that our ancestors suffered an event so as to reduce their numbers greatly,

[spoiler]Source: OG13 Q97[/spoiler]

Please explain the usage of "dash" here.
I think that "at some time in .....an event" defines "population bottleneck".

"greatly reducing.......variation." is modifying which clause and why?. Because of "dash", I don't know that on which "subject" this "ing" modifier is acting.

OA is B.
COMMA + VERBing should refer to the SUBJECT of the preceding clause. In A, reducing seems to refer to our ancestors, implying that OUR ANCESTORS were greatly reducing their numbers. The intended meaning here is that an EVENT greatly reduced their numbers. Eliminate A.

So that (in C) and so as (in E) imply PURPOSE. The result is a strange meaning: that our ancestors suffered for the PURPOSE of reducing their numbers. Not the intended meaning. Eliminate C and E.

In D, which seems to refer to an event, implying that our ancestors' numbers were reduced FROM an event -- a nonsensical meaning. Eliminate D.

The correct answer is B.

Like a colon, a dash at the end of a sentence serves to introduce information that explains or defines the preceding clause. The clause that PRECEDES the dash must be INDEPENDENT, but what follows the dash can take on different forms. In the OA, what follows the dash (that our ancestors suffered an event) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.


Hi Mitch,

1. I do not understand how D is incorrect. What is the non-sensical meaning that it is conveying?

2. Also, I do not understand the usage of that in the correct answer. As per your exp. you have mentioned that

that our ancestors suffered an event) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.

If these 2 noun clauses are parallel, shouldn't they be connected properly with a conjunction or semicolon?

3. Also, I have read Ron's explanation on Manhattan forum that dash acts as a comma, if such is the case then how can it connect 2 indep clauses?
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Sat Oct 15, 2016 3:27 am
[email protected] wrote:Hi Mitch,

1. I do not understand how D is incorrect. What is the non-sensical meaning that it is conveying?
D: an event from which their numbers were greatly reduced
Conveyed meaning:
Their numbers were greatly reduced from an event.
Here, the usage of from does not convey a logical meaning.
THE EVENT ITSELF reduced our ancestors' numbers.
Their numbers were not reduced FROM an event.
X was reduced from Y is both illogical and unidiomatic.
2. Also, I do not understand the usage of that in the correct answer. As per your exp. you have mentioned that

that our ancestors suffered an event[/i]) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.

If these 2 noun clauses are parallel, shouldn't they be connected properly with a conjunction or semicolon?
Dashes can connect almost anything.
Consider SC132 in the OG13:
https://www.beatthegmat.com/og-13-132-t168495.html
In the OA, dashes serve to interject an ENTIRE SENTENCE into the middle of another sentence.
Do not worry about the correct usage of a dash.
3. Also, I have read Ron's explanation on Manhattan forum that dash acts as a comma, if such is the case then how can it connect 2 indep clauses?
The two that-clauses in the OA are not independent.
Each serves as the direct object of believe.
WHAT do anthropologist believe?
They believe two things:
that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"
that at some time in the past our ancestors suffered an event that greatly reduced their numbers.
As mentioned above, a dash can serve to connect almost anything.
Here, a dash serves to connect two that-clauses, each a direct object of the preceding verb.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Legendary Member
Posts: 712
Joined: Fri Sep 25, 2015 4:39 am
Thanked: 14 times
Followed by:5 members

by Mo2men » Sat Oct 15, 2016 5:26 am
GMATGuruNY wrote:
[email protected] wrote:Hi Mitch,

1. I do not understand how D is incorrect. What is the non-sensical meaning that it is conveying?
D: an event from which their numbers were greatly reduced
Conveyed meaning:
Their numbers were greatly reduced from an event.
Here, the usage of from does not convey a logical meaning.
THE EVENT ITSELF reduced our ancestors' numbers.
Their numbers were not reduced FROM an event.
X was reduced from Y is both illogical and unidiomatic.
2. Also, I do not understand the usage of that in the correct answer. As per your exp. you have mentioned that

that our ancestors suffered an event[/i]) is a noun clause that explains and is parallel with the preceding noun clause (that the homogeneity is the result of a "population bottleneck"). Both noun clauses express what some anthropologists BELIEVE.

If these 2 noun clauses are parallel, shouldn't they be connected properly with a conjunction or semicolon?
Dashes can connect almost anything.
Consider SC132 in the OG13:
https://www.beatthegmat.com/og-13-132-t168495.html
In the OA, dashes serve to interject an ENTIRE SENTENCE into the middle of another sentence.
Do not worry about the correct usage of a dash.
3. Also, I have read Ron's explanation on Manhattan forum that dash acts as a comma, if such is the case then how can it connect 2 indep clauses?
The two that-clauses in the OA are not independent.
Each serves as the direct object of believe.
WHAT do anthropologist believe?
They believe two things:
that the genetic homogeneity evident in the world's people is the result of a "population bottleneck"
that at some time in the past our ancestors suffered an event that greatly reduced their numbers.
As mentioned above, a dash can serve to connect almost anything.
Here, a dash serves to connect two that-clauses, each a direct object of the preceding verb.
Hi GMATGuru,

Does that dash in this case work as 'and'. If not, how two dependent clauses are connected?? It would be something missing?
'anthropologist believe that..................that'

can you clarify pls?
Top
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pm
Location: New York, NY
Thanked: 13060 times
Followed by:1906 members
GMAT Score:790

by GMATGuruNY » Mon Oct 17, 2016 2:53 am
Mo2men wrote: Hi GMATGuru,

Does that dash in this case work as 'and'. If not, how two dependent clauses are connected?? It would be something missing?
'anthropologist believe that..................that'

can you clarify pls?
An appositive is a noun form that serves to explain or define another noun form.

OA: Some anthropologists believe that the genetic homogeneity evident in the world's people is the result of a "population bottleneck" - that at some time in the past our ancestors suffered an event that greatly reduced their numbers and thus our genetic variation.
Here, the two colored that-clauses are both noun forms in that each serves as a direct object of believe.
The blue that-clause serves to explain the red that-clause.
Thus, the blue that-clause can be considered an appositive for the red that-clause.

As I mentioned above, dashes can connect virtually ANYTHING.
Here, a dash connects one that-clause to another.
Since dashes can connect virtually ANYTHING, do not worry about the usage of the dash.
Focus on other issues.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Post new topic Locked
• Page 1 of 1