The Biological Question Thread

[Russ]

I see, so if there was a question on the exam that stated for example:
Why are the effects of gene therapy sometimes short lived?

Check however many marks it is, then list the appropriate amount of reasons in a paragraph: cell death before replication, immune response, low efficacy delivery etc.

On the HVR/STR thing, it seems to be a very subtle difference. From what I understand, the HVR is referring to the literal location on the chromosome where there is variation. An STR, however, describes the specific mutation/insertion that has been observed.

So it would seem that an STR could be at an HVR location.

[golden]

Thanks Russ.

[golden]

1. Are germ line cells diploid?

2.
It would be expected that the mass of the cell would increase measurably during
A. S phase.
B. G1 phase.
C. G2 phase.
D. M and C phases.

Answer: A.

Is DNA that heavy?

[golden]

Question 2
The chromosomes in a human somatic cell can be arranged to form a karyotype. In a normal
human male the chromosomes in a karyotype will be arranged into
A. 46 pairs of chromosomes, which include one large X chromosome and a smaller Y
chromosome.
B. 44 pairs of chromosomes, which include one large X chromosome and a smaller Y
chromosome.
C. 23 pairs of homologous chromosomes, including one large X chromosome and a
smaller Y chromosome.
D. 22 pairs of homologous chromosomes and one large X chromosome and a smaller
Y chromosome.

Apparently the answer is D.

Aren't the X and Y chromosome homologous to one another? I heard somewhere these two are homologous that's why meiosis cannot occur if you are missing a homologous chromosome such as a Y chromosome (in a male).

[lexitu]

The answer is C. Whoever wrote the exam should be punched in the head. You are right.

[lexitu]

To answer the other questions yes germline cells are diploid and I'll leave the other question to Russ but I'm thinking that it could be correct - if you've ever isolated DNA in a prac there's a shitload of it. But, having said that, I think it is a silly question and that there is also a likelihood that one of the G phases results in a large increase in mass because of the considerable growth that occurs in the cytoplasm either general activities or in preparation for mitosis.

Also, I have a question of my own: what's the difference between centrioles and centrosomes? They seem to have very similar functions. Relating to this, would any discussion about centrioles/centrosomes best be left out when answering a question on nuclear division so as not to discriminate against plants?

[yuuhei]

q2.
Isn't D? I remember my teacher said X and Y aren't homolgous so if its for a male then theres 22 pairs (autosomal) and 2 of the sex chromsomes (X and Y) and if it's a female then you can say there are 23 homologous pairs due to thier sex chromsomes both XX. I think....

[golden]

q2.
Isn't D? I remember my teacher said X and Y aren't homolgous so if its for a male then theres 22 pairs (autosomal) and 2 of the sex chromsomes (X and Y) and if it's a female then you can say there are 23 homologous pairs due to thier sex chromsomes both XX. I think....

I thought that too originally.

Source: http://www.wisegeek.com/what-are-homologous-chromosomes.htm

For example, human somatic cells  have 46 chromosomes within their nuclei, or 23 pairs of homologous chromosomes. One of each pair of the homologous chromosomes comes from the mother and one from the father. The human gamete cells, sperm and ova (eggs), each contain only 23 chromosomes. During fertilization, one sperm and one ovum fuse creating a cell that has the full complement of 46 chromosomes.

I remember Andrew Douch saying the two were homologous though.

[lexitu]

Just because they are not autosomal it doesn't mean that they are not homologous. Your teacher is plain wrong. (Sorry but this really frustrates me).

http://en.wikipedia.org/wiki/Homologous_chromosome
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SexChromosomes.html

[onerealsmartass]

It would be expected that the mass of the cell would increase measurably during
A. S phase.
B. G1 phase.
C. G2 phase.
D. M and C phases.

Answer: A.

i think the answer is right, he way that i interpretted it was when it said 'measurably' i thought of DNA replication because it does hapen quickly and the mass does increase a lot - i think

[golden]

Q. Why are the effects of gene therapy for CF so temporary?

A. Effects of gene therapy are temporary because the normal CFTR gene is not incorporated into the DNA of chromosomes.

Are we expected to know this? I would have said that it is due to the cells normally dying before the replication can take place in large enough amounts.

These questions are from Insight 2007 Exam 2 (Biology).

[golden]

To answer the other questions yes germline cells are diploid and I'll leave the other question to Russ but I'm thinking that it could be correct - if you've ever isolated DNA in a prac there's a shitload of it. But, having said that, I think it is a silly question and that there is also a likelihood that one of the G phases results in a large increase in mass because of the considerable growth that occurs in the cytoplasm either general activities or in preparation for mitosis.

Also, I have a question of my own: what's the difference between centrioles and centrosomes? They seem to have very similar functions. Relating to this, would any discussion about centrioles/centrosomes best be left out when answering a question on nuclear division so as not to discriminate against plants?

An associated pair of centrioles, arranged perpendicularly and surrounded by an amorphous mass of dense material (the pericentriolar material) constitutes the compound structure known as the centrosome.[1]

Centrioles are a very important part of centrosomes, which are involved in organizing microtubules in the cytoplasm.[8][9]  The position of the centriole determines the position of the nucleus and plays a crucial role in the spatial arrangement of the cell.

(Wikipedia)

[lexitu]

Insight exams are a load of crap (if you can't tell I'm in a feisty mood). If the information about the exact type of gene therapy is not given to you then you shouldn't have to know this. Some vectors incorporate DNA into the chromosomes, others insert it into the cell as free DNA so it is not replicated during mitosis.

I'm not sure if we need to know this. Nature of Biology covers this in unit three (and refers you onto this in its unit four discussion of gene therapy). Either adenoviruses or retroviruses can be used as vectors in humans. I think knowing the basics is suffice but it's hard to know really.

Thanks for the info on centrosomes/centrioles

[golden]

Question 22
Mitochondrial DNA (mtDNA) can be used to trace the evolutionary history of a species. A
characteristic of mtDNA not used to distinguish it from nuclear DNA is
A. lack of recombination.
B. descent through the maternal line.
C. high copy number.
D. molecular structure.

Can anyone explain?

[golden]

Question 17
Mitochondrial DNA is used to establish the relatedness between organisms in evolutionary biology, because
it
A. Is only inherited in males.
B. Has more genes than nuclear DNA.
C. Mutates more slowly than nuclear DNA.
D. Is only inherited in females

I'm pretty sure it mutates more rapidly than nuclear DNA.