kingpomba's question thread

[masonnnn]

Generally my definition is:

• Homologous - Same Structure Different Function
• Analogous - Different Structure Same Function

There is indeed something wrong. Most students use these as definitions and that's how they get tricked by questions like above.

Homologous is the same structure but the function does not need to be different, the key is that it is the same structure from the same origin/ancestry.

Analogous the key point isn't that they are different structures, it's that they evolved from different ancestry for the same purpose(which would often result in different structures overall, yet not always as seen with the eye). While usually they will present different structures with the same purpose, to avoid dropping marks like that question it's good to know if the structures evolved along completely seperate lines they can't be homologous so must be analogous.

[slothpomba]

Also, if the AA table wasn't given then you wouldn't be able to recognize it as a nonsense mutation.

AA Table wasn't included on this forum because i didnt want to make everyone scroll down heaps but it was on the exam.

I looked through nature of biology and the only mutations they mention are:

• Base Addition
• Base Substitution
• Base Deletion

And as a result of these:

• Excessive number of trinucleotide repeats
• Frameshifts

That's all the kinds of mutations Nature of Biology mentions.

I think its a rather well written book and almost always has the study design down pretty well, so ill just use those terms over the additional ones (nonsense,missense, ect) mentioned in A+ notes.

[slothpomba]

masonnnn, haha yes i realised this point last night after i looked up analogous/homologous once i got that question wrong.... I realise while usually analogous has different structure same function and the opposite for homologous, one of the key things is the evolutionary origin. Which is why they mention like this animal is an octopus and this is a vertebrate, even without really looking at the actual organs, i can tell that it is analogous since they do not share a recent common ancestor.

Just to help remind myself more than anything...

Analogous:

• Different Evolutionary Origin
• Do not share a recent common ancestor
• Usually similar function
• Usually different structure
• Both species in question experienced similar selective pressures to evolve this trait/organ
• An example of convergent evolution

Homologous:

• Similar evolutionary origin
• Share a recent common ancestor/ Belong to same class (eg mammals )
• Usually different function (Eg. Bats wings and whale flippers share similar bone structure up to a degree but have a different function, one is for propulsion through water, other is for propulsion through air, both are mammals)
• Usually similar structure
• The species being compared experienced different selective pressures and evolved accordingly
• An example of divergent evolution

[Caspar]

# Usually different function (Eg. Bats wings and whale flippers share similar bone structure up to a degree but have a different function, one is for propulsion through water, other is for propulsion through air, both are mammals)

Not sure about this. Homologous structures can also be vestigial, keep that in mind .

[slothpomba]

Yeah, thanks for that caspar, ill keep it in mind .

Anyway another one... i thought this one was debatable...


[Source:Insight 2006]

B & D are clearly Cultural.

We have A & C left...

I reasoned that Cultivation of crops required more technological evolution (tools to till the soil, irrigation, ect) than did hunting and gathering which doesn't really have much technological or biological evolution in it....

Banding together in groups to hunt and organising gathering is more cultural... well i think so anyway...

Maybe instead of it saying Cultivation of crops... it said something like move from hunter and gather society to harvesting crops and living in an agricultural society fair cop is cultural but it didn't exactly say it that way....

I selected Cultivation of Crops as the one that wasn't cultural...

You guys reckon im wrong or was it a bad question?

[slothpomba]

Anyone want to have a crack at the question in the last post(Cultural Evolution)...?

Anyway, When you do punnet squares, do you guys write down numerical ratios as well? Because i just write the genotype and no numbers but insight has told me twice now i should also write the numbers....



Not sure what i should do

[Russ]

To be maximally correct you should write the numbers but unless you're doing a recombinant it's always the same so i cbf'd

It's a situation where the person assessing it will know what you meant, but will take the mark off because you didn't explicitly state it

[slothpomba]

Yeah to me it just seems like such a bother to write the numbers but i shouldnt really miss out on an easy mark either i guess...

Ill probably just write them from now on

[stonecold]

VCAA won't make you do this.  They will always be like:

Showing working, what are the genotypes and phenotypes of the parents and the offspring for a cross betwenn II-4 and II-5.  Also give the proportions of each in your answer.

[slothpomba]

Another question hey?
It's relentless  :knuppel2:

[Source:TSSM 2007 Hard Exam!]

I understand how it can be dominant, because affected parents produce affected children but im not very clear on why it is sex linked

[slothpomba]

Does it matter which order i write alleles in, inside of a punnet square?

Eg
          D               d
----------------------------
D|        DD        |   dD
----------------------------
d |       Dd        |    dd

See the difference between the 2nd & 3rd squares? or doesnt it really matter at all

[Hutchoo]

Doesn't matter..
It will have the same result.

[slothpomba]

Yeah i know it'd have the same result but i thought there was maybe some convention we have to follow.....

Like writing the dominant ones first or the ones on-top first or something.

I have a bad habit of  changing the positions of the alleles around randomly.

[The Detective]

nope don't worry. I just follow a convention to prevent getting confused but doesn't really matter

[ivslt247]

Another question hey?
It's relentless  :knuppel2:
(Image removed from quote.)
[Source:TSSM 2007 Hard Exam!]

I understand how it can be dominant, because affected parents produce affected children but im not very clear on why it is sex linked

If a male is known to have the trait and you assume it is dominant X-linked, then all affected males MUST pass on this trait to all daughters and the male can only contribute its one X chromosome. As the trait is dominant, it doesnt matter what the mother contributes because the daughter will always be affected.