VCE Biology Question Thread

[plsbegentle]

Hey  :)Can someone help me with this question?
When looking at drosophila around the compost bin you came across a male and female with yellow eyes. Suppose the mutation was on an auto some and you wanted to establish if the yellow eyes was dominant or recessive to wild type (red) eyes.
a) outline the crosses you would carry out to establish which penotype is dominant. Yellow or wild type
b) Suppose you didn't know whether this gene was an on autosome or the x Chromosome. Outline the crosses you would perform to work this out
Thanks!

[Gogo14]

A) breed red eyes together until it produces a yellow eye, then you know that red eye trait is dominant, or do the same with yellow eyes until a red eyed offspring is produced.
B) breed a male with the dominant trait with a homologous female with the recessive trait. If any of daughters have the recessive trait, then it is autosomal, if not then it could be X linked.

[cindywindy]

Help please! Does a 'backcross' refer to crossing the F1 individual with any of their homologous parents (e.g. GG or gg),
and 'testcross' refer to crossing the F1 individual with only the recessive homologous parent (only gg)? I'm a little confused. Thank you in advance! 

[solution]

I'm having a hard time understanding and answering this question. Is recessive or dominant lethal alleles beneficial for evolution? Explain why.

I think it might be dominant because dominant allows carriers to survive in the population, which can spread the disease in successive generations. Is this correct?

[Sine]

I'm having a hard time understanding and answering this question. Is recessive or dominant lethal alleles beneficial for evolution? Explain why.

I think it might be dominant because dominant allows carriers to survive in the population, which can spread the disease in successive generations. Is this correct?

Recessive lethal alleles would allow carriers to survive - this means the organism requires two recessive alleles for it to not survive yet can survive as a hetrozygote or homozygous dominant.Dominant lethal alleles would mean the organism would only require a single dominant allele for it to not survive and only survive if it had two recessive alleles.

In terms of surviving a recessive lethal allele is favourable as carriers survive.

However in terms of evolution if it were a dominant lethal allele all organisms carrying that dominant allele would not survive hence unable pass this allele to the next generation therefore this would increase allele frequency of the recessive allele (non-lethal). Therefore the amount of organisms that were homozygous recessive (non-lethal) would approach 100% - in theory.

[vox nihili]

I'm having a hard time understanding and answering this question. Is recessive or dominant lethal alleles beneficial for evolution? Explain why.

I think it might be dominant because dominant allows carriers to survive in the population, which can spread the disease in successive generations. Is this correct?

Just to add to this, probably neither one. I'd say dominant is better though because those alleles disappear with the generation in which they arise, because dominant lethal alleles by definition cannot be passed down. Recessive lethals, however, can be passed down and can become embedded in the gene pool as such.

[Apink!]

Could someone clarify for me, the difference between point mutation and missense mutation?

[HighTide]

Could someone clarify for me, the difference between point mutation and missense mutation?

A point mutation is a mutation regarding one base-pair. From these, there are insertions, deletions and substitutions. The insertions and deletions are frame-shift mutations so they are the most dangerous.
A missense mutation is a point mutation which results in a change of amino acid.

[anotherworld2b]

In regards to this question
Q1. Patients who have suffered severe blood loss or dehydration have to be given large volumes of fluid. A fluid that is often given is a 0.9% solution of sodium chloride, known as normal saline. Why is saline solution given rather than just plain water?

If normal saline has the 0.9% of sodium chloride so that haemolysis doesn't occur
Would haemolysis occur if the fluid has 0.7% of sodium chloride?
What would happen if the fluid has 0.11% of sodium chloride? Would the red blood cells shrink?

I also wanted to ask for this question would it be correct?
Q2. Suggest reasons why epiphyses of long bones are composed of cancellous bone, while the diaphysis is composed of compact bone.

The diaphysis is composed of compact bone in the shaft of the bone. Compact bone is arranged in units called osteons or Haversian systems. Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix. Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.

The epiphysis is composed of spongy (cancellous) bone in the ends of long bones. Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces. It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. Spongy bone tissue is light and supports and protects the red bone marrow.

I am not sure why  epiphyses of long bones are made of cancellous bone. Is it to protects red bone marrow? then why is the diaphysis made of compact bone?

[vox nihili]

In regards to this question
Q1. Patients who have suffered severe blood loss or dehydration have to be given large volumes of fluid. A fluid that is often given is a 0.9% solution of sodium chloride, known as normal saline. Why is saline solution given rather than just plain water?

If normal saline has the 0.9% of sodium chloride so that haemolysis doesn't occur
Would haemolysis occur if the fluid has 0.7% of sodium chloride?
What would happen if the fluid has 0.11% of sodium chloride? Would the red blood cells shrink?

I also wanted to ask for this question would it be correct?
Q2. Suggest reasons why epiphyses of long bones are composed of cancellous bone, while the diaphysis is composed of compact bone.

The diaphysis is composed of compact bone in the shaft of the bone. Compact bone is arranged in units called osteons or Haversian systems. Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix. Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.

The epiphysis is composed of spongy (cancellous) bone in the ends of long bones. Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces. It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. Spongy bone tissue is light and supports and protects the red bone marrow.

I am not sure why  epiphyses of long bones are made of cancellous bone. Is it to protects red bone marrow? then why is the diaphysis made of compact bone?

At 0.7% no. At 0.11% sodium chloride, they'd still swell...0.11% is a high concentration of water.

Question two is not relevant to VCE. Not sure if it's an HSC question. If so, you're probably better to try that board.
For my part, I actually haven't got the faintest idea about why that's the case.

[mtse]

Q2. Suggest reasons why epiphyses of long bones are composed of cancellous bone, while the diaphysis is composed of compact bone.

The diaphysis is composed of compact bone in the shaft of the bone. Compact bone is arranged in units called osteons or Haversian systems. Osteons contain blood vessels, lymphatic vessels, nerves, and osteocytes along with the calcified matrix. Osteons are aligned in the same direction along lines of stress. These lines can slowly change as the stresses on the bone changes.

The epiphysis is composed of spongy (cancellous) bone in the ends of long bones. Spongy (cancellous) bone does not contain osteons. It consists of trabeculae surrounding many red marrow filled spaces. It forms most of the structure of short, flat, and irregular bones, and the epiphyses of long bones. Spongy bone tissue is light and supports and protects the red bone marrow.

I am not sure why  epiphyses of long bones are made of cancellous bone. Is it to protects red bone marrow? then why is the diaphysis made of compact bone?

Definitely not in VCE curriculum but was briefly mentioned in my first sem of uni lol so I'll attempt explaining it:
The way cancellous bone is formed is like a framework of thin spider-web like bone that grows in response to force/stress. The spaces between are often filled with marrow and blood vessels. The little bones (trabeculae) can continuously break and reform in response to the bone's usage. The epiphyses is located near the joint where it can experience different forces depending on how the joint is used, so being made of spongy bone/trabeculae basically makes the bone be able to adapt to its function.

While the diaphysis is the shaft of the bone - inside the shaft of long bones is the marrow cavity where bone marrow is stored. This requires strong protection which is offered by compact bone. Also along the shaft, the force received is generally unidirectional meaning that there is no need for spongy bone (which can respond to force from any direction), whereas compact bone provides support/strength in that direction. In terms of responding to stress, compact bone takes a longer time as the osteons can only shift slightly.

I do suggest looking up a diagram of a bone and having a look at the shape/structure of the two types of bone
Not 100% sure so don't hold this against me
Hope this helps a little

[anotherworld2b]

Thanks so much for the help
I was wondering for q1. If saline solution didnt have 0.9% of sodium chloride would it have a signicant impact?

[mtse]

I was wondering for q1. If saline solution didnt have 0.9% of sodium chloride would it have a signicant impact?

Yes if a pure water solution (saline solution without the 0.9% NaCl) was injected into a person, it would cause haemolysis (bursting of the red blood cells), which has many adverse effects

This can be explained by the phenomenon osmosis:
The concentration of solute inside the cell is equivalent to the concentration of solute in 0.9% saline solution. (This concentration is written as 300 milli-osmoles per litre). If pure water was injected into the blood stream then the water outside the red blood cell would be of a MUCHHHH lower concentration than inside the cell. Therefore to balance out the concentrations (reach equilibrium), water from outside the cell will diffuse INTO the cell. (Osmosis is the movement of water from an area of low concentration of solute to an area of high concentration of solute through a semi-permeable membrane) Depending on the amount of pure water injected, the amount of water that enters the cell may end up causing the cell membrane to burst and thus the cell will die. If this occurs systemically (all around the body), this means that the person will have no red blood cells = no transport of oxygen to organs = death

At 0.7% no. At 0.11% sodium chloride, they'd still swell...0.11% is a high concentration of water.

Sorry I don't completely agree with Mr T-Rav's  answers.
At 0.7% saline solution - the injected solution would be of lower solute concentration than inside the cell - therefore the cell is hypertonic to the fluid outside the cell and due to osmosis, water would enter the cell.
This may not cause haemolysis (as it is very close to 0.9% saline solution) but the cell will definitely swell.

At 0.11% saline solution - the injected solution would be of higher solute concentration than inside the cell - therefore the cell is hypotonic to the fluid outside the cell and water would leave the cell - i.e. the cell will shrivel. <-- just me being an idiot and thinking that 0.11>0.7 *facepalms*

[Apink!]

A point mutation is a mutation regarding one base-pair. From these, there are insertions, deletions and substitutions. The insertions and deletions are frame-shift mutations so they are the most dangerous.
A missense mutation is a point mutation which results in a change of amino acid.

Thank you Hightide!

Could someone tell me why this phrase INCORRECT?

PCR cannot use any type of DNA polymerase because the heat would denature the enzyme. I thought that this was true, and this is why we use taq polymerase in PCR. Can someone clarify this for me?

Thank you!

EDIT: I have another question attached!

[grannysmith]

Thank you Hightide!

Could someone tell me why this phrase INCORRECT?

PCR cannot use any type of DNA polymerase because the heat would denature the enzyme. I thought that this was true, and this is why we use taq polymerase in PCR. Can someone clarify this for me?

Thank you!

EDIT: I have another question attached!

Taq pol is a type of DNA polymerase

Re: attached q, I don't like it
But I'd say the first enzyme since the ends of the gene you see a GC/CG sequence; this would ensure the entire gene is isolated, and not truncated ( two extra bases is better than missing some). 3rd enzyme is undesirable because blunt ends, unlike sticky ends, would hinder the rejoining of fragments to reform the gene.

Hope that makes sense