OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment

Can someone please explain Replica Plating in steps...

Replica plating is a technique to identify the bacteria that have taken up the modified plasmid. Remember, some bacteria will not take up any new plasmid, and even if they do, there is still a chance that the plasmid that has been taken up is one that has not had a gene inserted.

Plasmids contain the DNA that codes for the antibiotic resistant chemicals that Bacteria may produce. Two such antibiotics that they are resistant to are ampicillin and tetracycline. Therefore, the genes that code for the chemicals that protect the bacteria from ampicillin and tetracycline are located somewhere in the plasmid.

Firstly, restriction enzymes are used to cut the tetracycline gene in half, so the desired gene can be inserted. Not all plasmids will have taken up the new gene - some plasmids may have jsut sealed up on itself.

Once inserted, the bacteria are grown on agar plates.

Once they have colonised, some are transferred onto ampicillin treated agar. Only those bacteria that have taken up the plasmid will survive.

Some bacterial cells from the ampicillin agar plate are transferred onto tertracycline agar. The bacteria that grow on here are obviously resistant to tetracycline, which means that the gene for tetracycline resistance still functions (So we know that the plasmids in these bacteria have not taken up the desired gene.).

So the bacteria that can grow on the ampicillin agar, but not on the tetracycline agar plate are the ones that have taken up the required gene.

Hope that helped.

Am I being stupid, or on page 118 of the OCR Heinemann Sue Hocking book, it describes the nature of the Bivalents in Metaphase 1, "lining up across the equator of the spindle"???

Maybe I am being dumb, but I thought the line across the middle of the cell was called the equator of the cell

Anyone care to explain homeobox genes?

Yea its meant to be across bivalents line up on the equator of the cell and probably something like attach onto the spindle fibre



Don't stress too much about them. Basically they are small lengths of DNA which code for transcription factors, and these are polypeptides which regulate the development of the body plan by switching on other genes, turning some off in a particular order which allows the embryo to develop and areas to become specialised etc.

Hox clusters are groups of homeobox genes. Thats it really!

Heyyy, I don't suppose anyone can help me out with UMS convesion for the A2 pratical? I need to know roughly what 34/40 is in UMS or maybe what it was equivalent to at AS.

Any help would be appreciated guys and girls! : )

Yes! I second this, I wanna know what my measly 33 is in UMS. Anyone?

Aaargh I need someone to explain the role of auxins in apical dominance pleaseee

Aaargh I need someone to explain the role of auxins in apical dominance pleaseee