duquesne's Bio 3/4 Question Thread

[aishuwa1995]

thiskid, are you good with III-1 is Bb and III-2 is B_ ?
Then cross them. Do Bb x B_ and Ennjy is saying that when you do this cross, the genotypes that you get are:
BB, BB, Bb, Bb, Bb, bb and so there are six genotypes and the chance of bb is 1/6.

Hey but Ennjy when you do Bb x B_ if you split it into the two possibilities: Bb x BB and Bb x Bb, I get:
Bb x BB
= 1/2 BB, 1/2 Bb
and then Bb x Bb
= 1/4 BB, 1/2 Bb, 1/4 bb
So that's where I'm getting confused... 

That's exactly where I'm confused duquesne9995

[duquesne9995]

thiskid, are you good with III-1 is Bb and III-2 is B_ ?
Then cross them. Do Bb x B_ and Ennjy is saying that when you do this cross, the genotypes that you get are:
BB, BB, Bb, Bb, Bb, bb and so there are six genotypes and the chance of bb is 1/6.

Hey but Ennjy when you do Bb x B_ if you split it into the two possibilities: Bb x BB and Bb x Bb, I get:
Bb x BB
= 1/2 BB, 1/2 Bb
and then Bb x Bb
= 1/4 BB, 1/2 Bb, 1/4 bb
So that's where I'm getting confused... 

That's exactly where I'm confused duquesne9995

Haha hi5 thiskid! 

No but in all seriousness, I don't know why my initial seemingly logical approach is failing me. Cos we all like maths  see attached picture... Why is that wrong? 
LOL btw when I was doing the q I didn't draw that tree diagram, I just thought of the first top branch that results in a white haired guinea pig.

[aishuwa1995]

thiskid, are you good with III-1 is Bb and III-2 is B_ ?
Then cross them. Do Bb x B_ and Ennjy is saying that when you do this cross, the genotypes that you get are:
BB, BB, Bb, Bb, Bb, bb and so there are six genotypes and the chance of bb is 1/6.

Hey but Ennjy when you do Bb x B_ if you split it into the two possibilities: Bb x BB and Bb x Bb, I get:
Bb x BB
= 1/2 BB, 1/2 Bb
and then Bb x Bb
= 1/4 BB, 1/2 Bb, 1/4 bb
So that's where I'm getting confused... 

That's exactly where I'm confused duquesne9995

Haha hi5 thiskid! 

No but in all seriousness, I don't know why my initial seemingly logical approach is failing me. Cos we all like maths  see attached picture... Why is that wrong? 
LOL btw when I was doing the q I didn't draw that tree diagram, I just thought of the first top branch that results in a white haired guinea pig.

hi5 duquesne9995 
LONG LIVE MATHS 
I don't really get the tree diagram  it's confusing me more...I like using punnet squares for biology 

[duquesne9995]

Okay, let's just wait for Ennjy or someone else to come in and save us both

[Jenny_2108]

Your tree diagram is so EPIC duquesne But actually, its not complicated like that

If you wanna use tree diagram



You don't have to consider the probability of genotype II3 from I1 and I2. They have no connection with probability of offsprings' genotype which III1 and III2 produce.
Think this way, the probability of your grandparents have sons or daughters doesn't affect the probability your parents have sons or daughter. They are INDEPENDENT, so you can't multiply all of those together to find the total probability

You just need to know II3's genotype is B- (BB or Bb). Thus, genotype of III2 is B- and draw this tree diagram
Anyway, I think the method I did in earlier post is easier. Tree diagram is so confusing

Btw, how can you draw the tree diagram on your laptop? I have to draw by hand though

[aishuwa1995]

I get it now Thank you Ennjy

[Jenny_2108]

^ You are welcome. Its so much fun when we do probability in bio together LOL

[duquesne9995]

Your tree diagram is so EPIC duquesne But actually, its not complicated like that

If you wanna use tree diagram

(Image removed from quote.)

You don't have to consider the probability of genotype II3 from I1 and I2. They have no connection with probability of offsprings' genotype which III1 and III2 produce.
Think this way, the probability of your grandparents have sons or daughters doesn't affect the probability your parents have sons or daughter. They are INDEPENDENT, so you can't multiply all of those together to find the total probability

You just need to know II3's genotype is B- (BB or Bb). Thus, genotype of III2 is B- and draw this tree diagram
Anyway, I think the method I did in earlier post is easier. Tree diagram is so confusing

Btw, how can you draw the tree diagram on your laptop? I have to draw by hand though

omg thanks so much Ennjy! I get it now. I was just making it overcomplicating it as usual =='
And I made my tree diagram on paint... LOL

[duquesne9995]

Okay so Q3 in Neap 2007 says

Chromosome number is reduced during meiosis because the process involves
A. a single cell division without any chromosome replication
B. two cell divisions without any chromosome replication
C. two cell divisions in which chromosome replication occurs once
D. two cell divisions in which half of the chromosomes are destroyed.

The solutions said the answer is C. And their explanation was:
Meiosis involves two successive divisions, so A cannot be correct. At the very start of meiosis,
chromosomes in the parent cell replicate themselves into pairs of chromatids. B is therefore incorrect. In the
first division, each pair of homologous chromosomes is separated to reduce the chromosome number in the
daughter nuclei by half. In the second division, the pairs of chromatids separate and enter the daughter cells.
At no stage in the process are chromosomes destroyed.

So ^^^ it is saying that DNA replication occurs "at the very start of meiosis" ?

BUT THENNN
In Neap 2009 Q5:
Chromosome number is reduced during meiosis because the process consists of
A. two cell divisions without any chromosome replication
B. a single cell division without any chromosome replication
C. two cell divisions and only a single round of chromosome replication
D. four cell divisions and no chromosome replication

And the solutions say that the answer is A this time, with the explanation that:
Replication of DNA occurs during interphase and then the DNA coils to form the chromosomes. Each
chromosome is comprised of two identical chromatids. Meiosis consists of two divisions. The first separates
the chromosome pairs and the second division separates the chromatids.

So now what? 

[aishuwa1995]

Okay so Q3 in Neap 2007 says

Chromosome number is reduced during meiosis because the process involves
A. a single cell division without any chromosome replication
B. two cell divisions without any chromosome replication
C. two cell divisions in which chromosome replication occurs once
D. two cell divisions in which half of the chromosomes are destroyed.

The solutions said the answer is C. And their explanation was:
Meiosis involves two successive divisions, so A cannot be correct. At the very start of meiosis,
chromosomes in the parent cell replicate themselves into pairs of chromatids. B is therefore incorrect. In the
first division, each pair of homologous chromosomes is separated to reduce the chromosome number in the
daughter nuclei by half. In the second division, the pairs of chromatids separate and enter the daughter cells.
At no stage in the process are chromosomes destroyed.

So ^^^ it is saying that DNA replication occurs "at the very start of meiosis" ?

BUT THENNN
In Neap 2009 Q5:
Chromosome number is reduced during meiosis because the process consists of
A. two cell divisions without any chromosome replication
B. a single cell division without any chromosome replication
C. two cell divisions and only a single round of chromosome replication
D. four cell divisions and no chromosome replication

And the solutions say that the answer is A this time, with the explanation that:
Replication of DNA occurs during interphase and then the DNA coils to form the chromosomes. Each
chromosome is comprised of two identical chromatids. Meiosis consists of two divisions. The first separates
the chromosome pairs and the second division separates the chromatids.

So now what? 

uh..this is really weird but I'm pretty sure NEAP was right in 2007
Watch this http://www.biostudio.com/d_%20Meiosis.htm 

[itsdanny]

I'm in a bit of a hurry, can someone please tell me what was the hardest VCAA exam? (determined by the cutoff mark from the graded distributions)
Thanks,

[aishuwa1995]

I'm in a bit of a hurry, can someone please tell me what was the hardest VCAA exam? (determined by the cutoff mark from the graded distributions)
Thanks,

2008