VCE Biology Question Thread

[vox nihili]

Why is it that if alleles for a particular genes are further apart on a chromosomes the more likely they are to be swapped in the "crossing over" process of meiosis?

Cross overs are completely random (not true but let's assume that it is) and so the more space between genes the more chance it is that there'll be a cross over event between them.

[RazzMeTazz]

"If the loci of two genes are on the same chromosome they are linked."

Does this mean only alleles for different genes, can be linked?

Can one chromosome contain two different alleles for a particular gene?

[RazzMeTazz]

Can genes which were initially linked become un-linked through crossing over and hence recombinations?

[vox nihili]

"If the loci of two genes are on the same chromosome they are linked."

Does this mean only alleles for different genes, can be linked?

Can one chromosome contain two different alleles for a particular gene?

That's precisely what it means. You can't have alleles from the same gene that are linked...

Technically yes, but that means there are two copies of that gene. There's one allele per gene locus.

Can genes which were initially linked become un-linked through crossing over and hence recombinations?

When it talks about linked genes, it means linked gene loci. So no.

[grannysmith]

Is it better to separate telophase and cytokinesis?
Also, is this an accurate description of cytokinesis: cytoplasm divides, cell membrane pinches into two cells. In plant cells, new cell walls are produced which divide cytoplasm into two cells.

[MM1]

Is it better to separate telophase and cytokinesis?
Also, is this an accurate description of cytokinesis: cytoplasm divides, cell membrane pinches into two cells. In plant cells, new cell walls are produced which divide cytoplasm into two cells.

Mitosis is strictly PMAT. Cytokinesis is not a part of the process; rather it is related. Some cells such as a cluster of muscles cells don't undergo cytokinesis, I believe they form what is called a Syncytium, which is basically a joined cluster of cells that don't under go cytoplasmic division:)

Also, I think you should add that the new cells walls produced by plant cells are called a cell plate. Otherwise, pretty decent description.

[MM1]

Can someone please explain polygenes and multiple alleles? Thanks.

[grannysmith]

How should I explain apoptosis?
Apoptosis is programmed cell death, and may be performed to regulate cell numbers, remove unwanted cells or to destroy virally infected cells.
Extrinsic pathway:
Death ligand binds to specific receptor on target cell.
This triggers transduction and a cascade of reactions within the cell ensues.
Caspases are activated which break down nucleus and cytoplasm, causing the cell membrane to bleb.
Cellular fragments are enclosed in apoptotic bodies, and are phagocytosed by phagocytes.
This ultimately leads to cell death.

The intrinsic pathway is less applicable to the study design, no?

[RazzMeTazz]

During nuclear division can chromosomes be seen with a light microscope?

[RazzMeTazz]

If chromosome 21 becomes translocated onto chromosome 14 this can result in the individual producing gametes with two of chromosome 21 and one of chromosome 14. If this gamete fuses with a normal haploid sperm cell, a child with down syndrome will result (Trisomy 21)

So if the individual's chromosome 21 becomes translocated onto chromosome 14, they would have a total of 45 chromosomes.
How does this uneven number of chromosomes assemble into homologous pairs during meiosis to produce gametes?

Because individuals with Turner syndrome (also with 45 chromosomes) cannot produce gametes in meiosis, as they have an uneven number of chromosomes.

Why is the translocation of chromosome 21 onto chromosome 14, an exception?

[RazzMeTazz]

In the nucleus of a human cell, do all of the paternal chromosomes have the same DNA molecule on them and all of the maternal chromosomes have the same DNA molecule?

[vox nihili]

In the nucleus of a human cell, do all of the paternal chromosomes have the same DNA molecule on them and all of the maternal chromosomes have the same DNA molecule?

No, each chromosome is different.

[Rishi97]

I've read somewhere that the gender of a particular species, depends on the temperatures at which it has been incubated at. So when heated at a particular temperature, it may either be male or female. This is really interesting stuff for me but I don't really understand why this occurs. What exactly causes this?
Thanks for any clarification 

[vox nihili]

I've read somewhere that the gender of a particular species, depends on the temperatures at which it has been incubated at. So when heated at a particular temperature, it may either be male or female. This is really interesting stuff for me but I don't really understand why this occurs. What exactly causes this?
Thanks for any clarification 

Presumably the developmental proteins that go on to make sex structures are activated/deactivated at particular temperatures. Thus, the incubation temperature determines which set of proteins is activated and which sex is created.

[nerdmmb]

I've got a few questions relating to genetics..

1. If females have already developed their ovum while they were in their mother's womb then would that mean that they do not undergo meiosis after birth?

2. Does helicase unwind the DNA molecule during transcription? If not, then what does?

3. What is monomorphism?

4. What is DNA profiling and DNA fingerprinting and the difference between them two?

5. How is polymerase chain reaction different from gene cloning?