VCE Biology Question Thread

[Gogo14]

What does the circle with the dot mean?

Its a carrier(I.e heterozygous person with the trait in their genotype,but not in their phenotype).

[vox nihili]

Ahh, I shall try again

Restriction enzymes are enzymes used to cut out parts of DNA. They do this by cutting at unique nucleic acid sequences called 'recognition sites'. As enzymes have specific shapes in order to act on specific substrates, the enzyme will travel down the DNA strand until it finds the shape specific to the enzyme - in other words, the recognition site. The enzyme will then cleave through the sugar-phosphate backbone ( I admit, I don't know exactly how this works ). The restriction enzyme will leave two types of ends on the helix, being blunt ends and sticky ends, with blunt ends leaving no nucleobases overhanging, and sticky ends leaving nucleobases overhanging.

EDIT: Yes, I think Plsbegentle's explanation was correct and concise (always good to be). I don't know if it went exactly into the how, though, as the original question posed - but this is something I am not too confident on myself!

Great explanations by both of you. Really great to see Remember if somebody asks a question, even if you're not entirely sure you should always give it a crack. Worst thing that can happen is you can be wrong—and all that means is I'll pop in and set you straight


One slight thing to note here. Restriction enzymes cut the phosphodiester bond, not the bond between phosphate and the deoxyribose. Otherwise, perfect.


Can anyone explain how you can use restriction enzymes to detect the identity of a gene?

[Gogo14]

Restriction enzymes are enzymes which bind to a specific sequence of nucleotides on the DNA, and splits the strand apart by breaking phosphodiester bonds.
Plsbegentles definition was pre gud.

[vox nihili]

Restriction enzymes are enzymes which bind to a specific sequence of nucleotides on the DNA, and splits the strand apart by breaking phosphodiester bonds.
Plsbegentles definition was pre gud.

How can they be used to identify a gene, or sequence of DNA?

[Gogo14]

Because you know the specific base sequences where the RE cuts the DNA, if you know the base sequence of a gene, you can therefore use REs to cut a strand of DNA into fragments where one of those fragments is a perfectly cut and intact gene.
Then you place the resultant fragments in gel electrophoresis, and if you know the number of base pairs of the gene, you can identify the fragment that is the gene(if the fragment is perfectly cut). Or you could estimate the relative size of the gene compared to the original strand, and read of the gel electrophoresis by identifying which one is larger/smaller.

[vox nihili]

Because you know the specific base sequences where the RE cuts the DNA, if you know the base sequence of a gene, you can therefore use REs to cut a strand of DNA into fragments where one of those fragments is a perfectly cut and intact gene.
Then you place the resultant fragments in gel electrophoresis, and if you know the number of base pairs of the gene, you can identify the fragment that is the gene(if the fragment is perfectly cut). Or you could estimate the relative size of the gene compared to the original strand, and read of the gel electrophoresis by identifying which one is larger/smaller.

All correct, except the very last sentence. If your gene is 1000bp long, you can cut any random 1000bp and it will look the same size. Also practically very difficult to achieve. Great work though!


Can anyone explain how gel electrophoresis works?

[Calebark]

What does the circle with the dot mean?

As Gogo14 said, it is a carrier, but it should be noted that you won't always be explicitl told when somebody is a carrier - that is, the dot won't always be present.

Can anyone explain how gel electrophoresis works?

Gel electrophoresis works by measuring how far proteins or DNA fragments move towards an electrode (for example, DNA is negatively charged, so it would move to a positive terminal) in comparison to a set of standards of known size. This is achieved by dissolving the sample in a buffer, then placing said sample in wells made within agarose gel. An electric current is then added. The sample will then move to the electrode of opposing charge. As the agarose gel is a matrix, it will take longer for larger molecules to navigate their way through. Once complete, the distance of each sample travelled is compared to said set of standards of known size.

EDIT : Ahh, I forgot to add my probes.

[vox nihili]

As Gogo14 said, it is a carrier, but it should be noted that you won't always be explicitl told when somebody is a carrier - that is, the dot won't always be present.

Gel electrophoresis works by measuring how far proteins or DNA fragments move towards an electrode (for example, DNA is negatively charged, so it would move to a positive terminal) in comparison to a set of standards of known size. This is achieved by dissolving the sample in a buffer, then placing said sample in wells made within agarose gel. An electric current is then added. The sample will then move to the electrode of opposing charge. As the agarose gel is a matrix, it will take longer for larger molecules to navigate their way through. Once complete, the distance of each sample travelled is compared to said set of standards of known size.

EDIT : Ahh, I forgot to add my probes.

The one line I'll add for clarity is that the distance travelled by a DNA fragment is inversely proportional to its size.

Absolutely nailed it, great work!

Really proud of everyone here :')

[Apink!]

Hi all 

I would appreciate help for this question. I thought it would be 1/4, but the answer is 1/16

[vox nihili]

Hi all 

I would appreciate help for this question. I thought it would be 1/4, but the answer is 1/16

To get the condition, the child has to get the disease gene AND have type O blood.


The chances of getting the disease gene are 1/4 (because both parents are heterozygous for it) and the chance of being type O from those parents is also 1/4 (because they are heterozygous for this characteristic too).

So 1/4 * 1/4=1/16

[Apink!]

Oh, I see now! Thank you so much!

[epichedgehog]

Hi everyone,

There's a question in my textbook which I'm not too sure about. It talks about selectively breeding a certain species of cattle (Holstein cows) and how, over many years, it has resulted in high milk yield (the desired phenotypic trait) but declining fertility. (There's two line graphs, one for milk yield which is increasing and one for fertility which is decreasing).
The question is: What does this suggest about where the genes for milk production and fertility are carried?

Sorry if it's not clear enough. I can add more explanation for clarification if needed.

Thanks! .

[vox nihili]

Hi everyone,

There's a question in my textbook which I'm not too sure about. It talks about selectively breeding a certain species of cattle (Holstein cows) and how, over many years, it has resulted in high milk yield (the desired phenotypic trait) but declining fertility. (There's two line graphs, one for milk yield which is increasing and one for fertility which is decreasing).
The question is: What does this suggest about where the genes for milk production and fertility are carried?

Sorry if it's not clear enough. I can add more explanation for clarification if needed.

Thanks! .

The genes are linked (i.e. on the same chromosome*). Can you explain from that now?








*don't worry about the asterix if you're a VCE kid, just acknowledging for those who are beyond VCE that this isn't technically a correct definition of linkage. They are on the same chromosome, but have to be within a certain distance of each other.

[epichedgehog]

The genes are linked.. meaning that they are more likely to be passed down together (on the one chromosome) to offspring? I'm not really sure :/ for some reason my class hasn't covered linked genes yet.. we're kind of skipping between AOS 1 and AOS 2

[plsbegentle]

What does the circle with the dot mean?

Can someone confirm for me, that's a autosomal dominant right?