lolipopper's Bio 3+4 Questions

[lolipopper]

i need help with the linkage testing.

Is the following true?
In a dihybrid cross if the proportion of offspring are in 9:3:3:1 ratio (in monohybrid 3:1) than the genes are not linked.
If any other ratio than the genes are linked.

[vox nihili]

i need help with the linkage testing.

Is the following true?
In a dihybrid cross if the proportion of offspring are in 9:3:3:1 ratio (in monohybrid 3:1) than the genes are not linked.
If any other ratio than the genes are linked.

For the purposes of the VCE course, yep

[pi]

Made a new topic, hi-jacking someone else's thread isn't polite

[lolipopper]

I thought it was like anybody could ask questions there

[pi]

I haven't paid much attention to that thread (leave it to the Vic mods) but usually on AN "xxxx's <subject> question thread" usually refers to questions from user "xxxx" that they would like answered (this is different to topics like Chemistry 3/4  2013 Thread where it's open to anyone). Just to have all their questions in one place to find answers later if they want to go over something again (organisation-wise). I try and split questions from other people as it isn't too polite.

You can post your questions here

[Stick]

i need help with the linkage testing.

Is the following true?
In a dihybrid cross if the proportion of offspring are in 9:3:3:1 ratio (in monohybrid 3:1) than the genes are not linked.
If any other ratio than the genes are linked.

Just remember that this outcome results from the cross of two F1 (heterozygous dominant) parents. Some people assumed that ratio for all parental genotypes in our SAC and lost a lot of marks.

[lolipopper]

question: how does an organism get two copies of each chromosome?

[vox nihili]

question: how does an organism get two copies of each chromosome?

That occurs when DNA is replicated. So in mitosis, the DNA is completely copied before the cells divide (each cell starts with two sets, so each daughter cell gets two sets). The other option of course is the fusion of two haploid cells, which makes a zygote that is diploid (two sets of chromosomes). That particular cell is the progenitor of all other body cells, which form via mitosis as I described

Just think of the zygote as the first cell. One chromosome from mum, one chromosome from dad. All cells after that are created by mitosis and thus are direct copies

[lolipopper]

question:

-it is said that don't presume that dominant traits will be more frequent than recessive trait. why is this?

[psyxwar]

question:

-it is said that don't presume that dominant traits will be more frequent than recessive trait. why is this?

well, they could result in a phenotype selected against and thus the dominant allele would be less frequent in that population

[vox nihili]

question:

-it is said that don't presume that dominant traits will be more frequent than recessive trait. why is this?

There are some cases where the heterozygote will be the best condition, so the recessive allele is just as important in that situation as the dominant.

[the girl at the rock show]

question:

-it is said that don't presume that dominant traits will be more frequent than recessive trait. why is this?

Like others have said, the most common phenotype is the one that gives a selective advantage, not necessarily the dominant one.

Some examples:
 - Achondroplastic dwarfism is a dominant trait, but is very uncommon.
 - Blood group O (recessive) is the most common blood type.

t-rav mentioned some cases where the heterozygote is the best condition. Sickle cell disease is an example of this. The 'sickle haemoglobin' allele is recessive. People homozygous for the condition will die because they'll have 100% sickle haemoglobin (which is defective). However, the heterozygous condition is desirable in some regions of the world because the sickle cell allele also confers malaria resistance.

[lolipopper]

Question from http://www.vcaa.vic.edu.au/Documents/exams/biology/biol1_exam_2007.pdf

for Q13, why is D not a reasonable choice. It says in the box that the 4year old was immunised at 18 months. So wouldn't saying he previously received an injection of chicken pox antibodies be correct?

[Russ]

Have you covered the difference between active and passive immunisation in class? Immunisations don't necessarily have to be preformed antibodies.

[lolipopper]

i thought vaccines were attenuated antigen displaying organisms while immunisations were simple antibodies.

Edit: Its all good Russ. i think i read it wrong from the text book. So would it be right to say that immunisations include vaccines, shots of antibodies or any other treatment that provides and individual with immunity against a pathogen?