practice exam questions thread

[slothpomba]

I think its important to remember apoptosis is different from necrosis as well. Necrosis is just the death of tissue, it isn't kind of organised, planned or induced by the body. If you burn yourself or get hit with a baseball bat, the corresponding death of tissue is necrosis (VCE correct anyway). Just be careful because sometimes they might try to trick you up on this, i don't know if they've changed the study design to make it a little more clear though.

[Yacoubb]

I think its important to remember apoptosis is different from necrosis as well. Necrosis is just the death of tissue, it isn't kind of organised, planned or induced by the body. If you burn yourself or get hit with a baseball bat, the corresponding death of tissue is necrosis (VCE correct anyway). Just be careful because sometimes they might try to trick you up on this, i don't know if they've changed the study design to make it a little more clear though.

I think that knowing that apoptosis is a programmed mechanism should probably be the best way for us to identify it as apoptosis, rather than necrosis. E.g. DNA damage, cells no longer needed, embryonic development, etc.

[neonperson]

http://www.vcaa.vic.edu.au/Documents/exams/biology/2006biol2-w.pdf

Question 8 of the multiple choice I don't understand
How/why is it D?

[Yacoubb]

http://www.vcaa.vic.edu.au/Documents/exams/biology/2006biol2-w.pdf

Question 8 of the multiple choice I don't understand
How/why is it D?

It mentions that the two genes are not independently assorted. This means that the two genes are actually linked.

SsWw x SsWw, if the two genes were unlinked, would result in offspring phenotypes in a 9:3:3:1 ratio. However, because the genes are linked, you're going to expect that there is a greater proportion of offspring with parental phenotypes relative to recombinant phenotypes. So, this means that to begin with, you're expecting to cross offspring with either of the parental phenotype (not recombinant), and so in fact, you're stemming it back to the parental phenotypes, long/straight and short/wavy, and so most offspring would show this phenotype than sat short/straight (which would be a recombinant phenotype). Hence, D is the answer.

I hope this helped.

[swagsxcboi]

It mentions that the two genes are not independently assorted. This means that the two genes are actually linked.

SsWw x SsWw, if the two genes were unlinked, would result in offspring phenotypes in a 9:3:3:1 ratio. However, because the genes are linked, you're going to expect that there is a greater proportion of offspring with parental phenotypes relative to recombinant phenotypes. So, this means that to begin with, you're expecting to cross offspring with either of the parental phenotype (not recombinant), and so in fact, you're stemming it back to the parental phenotypes, long/straight and short/wavy, and so most offspring would show this phenotype than sat short/straight (which would be a recombinant phenotype). Hence, D is the answer.

I hope this helped.

I don't see how SsWw x SsWw is relevant here?
I mean 9:3:3:1 is exactly right but the question says it's a test cross. SsWw x ssww
If the genes were unlinked then you'd get equal 1:1:1:1 ratio 
If the genes were linked and crossing over did not occur you'd get a 1:1 ratio
In this case, the genes were linked and crossing over occurred, therefore the parental genotypes would be greater in number than recombinant genotypes. you'd expect parental genotypes to be equal in number and recombinant genotypes to also be equal.
thus, D is the correct answer

[Smiley_]

does natural selection act upon the genotype of the phenotype i have just seen to different views
or is it different if they can just selection ?

[Yacoubb]

does natural selection act upon the genotype of the phenotype i have just seen to different views
or is it different if they can just selection ?

Natural selection acts on the phenotypes of members of a population, differentially.

[Snorlax]

To act on the phenotype, doesn't the genotype have to be affected?

[Stevensmay]

To act on the phenotype, doesn't the genotype have to be affected?

Acting on the phenotype simply means that the decision is based on the physical characteristic of something.
Eg. Lets say you've got a genotype that means your more likely to be tall (not really but hey).
If I come up to you and say 'you're very tall,' it's because I've acted on your phenotype (I've looked and see how tall you are). I can't act on your genotype as I simply do not know it.

In the long run the genotype of the population may be affected, due to natural section dis/advantaging certain phenotypes and consequentially not/favouring the respective genotype.

[Snorlax]

What i'm trying to say is the genotype determines a phenotype.
So why couldn't you say "Natural selection acts on the genotype of members of a population"

[swagsxcboi]

What i'm trying to say is the genotype determines a phenotype.
So why couldn't you say "Natural selection acts on the genotype of members of a population"

since the selection pressures will disadvantage/advantage a phenotype, it's wrong to say it acts on a genotype. however, natural selection will cause change in allele frequencies of the allele that codes for the favoured trait.
For example, in most cases (disregarding heterozygous advantages), heterozygous individuals and homozygous dominant individuals will be favoured equally in a population due to expressing the same phenotype. Therefore it's incorrect to say that natural selection acts on the genotype of members of a population.

[Smiley_]

Natural selection acts on the phenotypes of members of a population, differentially.

because in the atar note book it says it act on the genotype ?

[slothpomba]

because in the atar note book it says it act on the genotype ?

Pretty sure thats incorrect...

Phenotype is the practical outcome and the thing that selection operates on.

[Yacoubb]

because in the atar note book it says it act on the genotype ?

It definitely acts on phenotype, not genotype.

[Snorlax]

http://www.vcaa.vic.edu.au/Documents/exams/biology/bioassessrptnov06.pdf

Q1.d)
It states that "the mice with grey coats were known to be homozygous" in the first paragraph.
The genotypic ratio is: 1/4 YY, 1/2 Yy, 1/4 yy.
Wouldn't that mean a phenotypic ratio is: 2 yellow, 2 grey?

I know YY couldn't be grey, but it does say "the mice with grey coats were known to be homozygous".