Yacoubb's Bio 3+4 Questions

[Yacoubb]

Okay so just clarifying a couple of things:

A selecting agent is a biotic or abiotic factor that selects for or against a particular phenotype in a population, living in a given environment. Selection pressure is exerted upon a population living in a given environment, by the selecting agent.

Also, do we have to know the three different forms of natural selection:
(a) Directional selection
(b) Stabilising selection
(c) Disruptive selection

[vox nihili]

Okay so just clarifying a couple of things:

A selecting agent is a biotic or abiotic factor that selects for or against a particular phenotype in a population, living in a given environment. Selection pressure is exerted upon a population living in a given environment, by the selecting agent.

Also, do we have to know the three different forms of natural selection:
(a) Directional selection
(b) Stabilising selection
(c) Disruptive selection

I agree with that definition, though there is very little difference between the two, if there is even a difference at all.

You don't need to know about the different types of selection. As I've said, you're not expected to understand population genetics. As an aside though, I think you'd enjoy what we're doing in maths at the moment (which is all about that!).

[Yacoubb]

In terms of a historical basis, how much should I know about the Darwin-Wallace theory of evolution by natural selection other than the fact that it is a theory that agents of selection act differentially on different phenotypes present amongst members of a population, without any human intervention?

Should I know about how this theory of evolution compares with other theories - for instance, that Darwinism provides a substantial means by which evolution can occur, and also that Darwinism explains how evolution is a change in the genetic composition of a population over many successive generations, opposed to evolution occurring in just one or few members of a population in a short period of time?

[vox nihili]

In terms of a historical basis, how much should I know about the Darwin-Wallace theory of evolution by natural selection other than the fact that it is a theory that agents of selection act differentially on different phenotypes present amongst members of a population, without any human intervention?

Should I know about how this theory of evolution compares with other theories - for instance, that Darwinism provides a substantial means by which evolution can occur, and also that Darwinism explains how evolution is a change in the genetic composition of a population over many successive generations, opposed to evolution occurring in just one or few members of a population in a short period of time?

You should understand the key concepts and postulates of the Darwin-Wallace theory, but the historical context is just there because textbooks love to pretend that they're fancy.

[Yacoubb]

You should understand the key concepts and postulates of the Darwin-Wallace theory, but the historical context is just there because textbooks love to pretend that they're fancy.

Thanks for that!

[vox nihili]

Thanks for that!

You can buy the chapter from Origin of Species about natural selection (It's called On Natural Selection) as one of those penguin classics. It's a good read. Darwin's quite funny really. He's just like a dotting old man who really loves his flowers hahah. That and he uses the words progeny, genera and commonest all the time...it's just so British.

[alondouek]

You can buy the chapter from Origin of Species about natural selection (It's called On Natural Selection) as one of those penguin classics. It's a good read. Darwin's quite funny really. He's just like a dotting old man who really loves his flowers hahah. That and he uses the words progeny, genera and commonest all the time...it's just so British.

I recently bought the penguin classics version of On the Origin of Species. Not necessary for VCE, but if you have any spare time, it's a brilliant read, as t-rav says.

[Yacoubb]

Could someone verify whether my knowledge of sticky ends/ blunt ends is accurate?

Sticky ends are cut, DNA fragments with overhanging (exposed) nitrogenous bases, formed when a restriction enzyme cuts a strand of DNA at a diagonal to its complementary strand.

Blunt ends are cut, DNA fragments with no overhanging (exposed) nitrogenous bases, formed when a restriction enzyme cuts two complementary DNA polynucleotide strands at the same location.

Also, would it be useful to mention that restriction enzymes cut at a restriction site, which is in fact located in a specific recognition sequence? It's just because from what I understand, a restriction sequence is a sequence of DNA of about 4-8 nitrogenous bases that a restriction endonuclease recognises. Then, within that recognition, is a restriction site where the restriction enzyme actually cuts. What I'm trying to say is that it may be useful to distinguish between a recognition sequence and a restriction site.

Thanks!

[vox nihili]

Could someone verify whether my knowledge of sticky ends/ blunt ends is accurate?

Sticky ends are cut, DNA fragments with overhanging (exposed) nitrogenous bases, formed when a restriction enzyme cuts a strand of DNA at a diagonal to its complementary strand.

Blunt ends are cut, DNA fragments with no overhanging (exposed) nitrogenous bases, formed when a restriction enzyme cuts two complementary DNA polynucleotide strands at the same location.

Also, would it be useful to mention that restriction enzymes cut at a restriction site, which is in fact located in a specific recognition sequence? It's just because from what I understand, a restriction sequence is a sequence of DNA of about 4-8 nitrogenous bases that a restriction endonuclease recognises. Then, within that recognition, is a restriction site where the restriction enzyme actually cuts. What I'm trying to say is that it may be useful to distinguish between a recognition sequence and a restriction site.

Thanks!

yes to all

[Yacoubb]

yes to all

Thanks so much

[Yacoubb]

Are the following descriptions for each step of PCR correct? Thanks

(1) DNA is heated to 95^oC for 2 minutes; the DNA molecule denatures, breaking the hydrogen bonds between the two polynucleotide strands and dissociating the DNA molecule.
(2) DNA is subject to 55^oC for 2 minutes; a primer (synthetic, single strand of DNA or RNA) anneals (hybridises) to the 3' end of the single DNA strands by complementary base pairing.
(3) DNA is heated to 72^oC for 1 minute; the primer is extended by taq polymerase ( a type of DNA polymerase), which collects free DNA nucleotides to construct complementary polynucleotide strands to the target sequence.
(4) The cycle is repeated.

Is it accurate to say the following about primers:

• A primer is a synthetic, single strand of DNA or RNA that brackets the target DNA sequence that scientists wish to amplify.

[swagsxcboi]

Are the following descriptions for each step of PCR correct? Thanks

(1) DNA is heated to 95^oC for 2 minutes; the DNA molecule denatures, breaking the hydrogen bonds between the two polynucleotide strands and dissociating the DNA molecule.
(2) DNA is subject to 55^oC for 2 minutes; a primer (synthetic, single strand of DNA or RNA) anneals (hybridises) to the 3' end of the single DNA strands by complementary base pairing.
(3) DNA is heated to 72^oC for 1 minute; the primer is extended by taq polymerase ( a type of DNA polymerase), which collects free DNA nucleotides to construct complementary polynucleotide strands to the target sequence.
(4) The cycle is repeated.

Is it accurate to say the following about primers:

• A primer is a synthetic, single strand of DNA or RNA that brackets the target DNA sequence that scientists wish to amplify.

I don't think a RNA primer is used in PCR.

[Yacoubb]

I don't think a RNA primer is used in PCR.

It can be used; its just better to use a DNA primer for stability and DNA primers anneal more efficiently to 3' end of polynucleotide strands than RNA primers.

But I see what you mean Thanks!

[swagsxcboi]

It can be used; its just better to use a DNA primer for stability and DNA primers anneal more efficiently to 3' end of polynucleotide strands than RNA primers.

But I see what you mean Thanks!

also, I think you'd have to remove it to replace it with DNA nucleotides (using DNA polymerase), which isn't spoken of in PCR

[Yacoubb]

Can someone please explain what an STR is?