Edexcel A2 Biology Unit 5 (6BIO5) - 27/01/2011- OFFICIAL THREAD !

I'll just give you a taste of it




cheers

Everyone please read this

Thnx a lot i really appreciate this.
Sorry to be annoying but is there any way you could upload a pdf file of the examiner's report instead of on scribd. Sorry again and thnx for your help.

You can directly download the examiner report from here[it's too big to be uploaded on TSR]
http://www.filedropper.com/6bi0501pef2010

Questions on plants , muscles and some genetics in the file-

hey u doing a2 bio ??

You can directly download the examiner report from here[it's too big to be uploaded on TSR]
http://www.filedropper.com/6bi0501pef2010

Questions on plants , muscles and some genetics in the file-

I'll be posting more stuff soon

Yes!!I'm doin unit 5 ..between u Guys know the duration for unit 5 has been increased to 1 hr 45 mins..they added 15 Mins extra from jan 2011.....I love EdexceL

I'll just give you a taste of it




Everyone please read this

Yes!!I'm doin unit 5 ..between u Guys know the duration for unit 5 has been increased to 1 hr 45 mins..they added 15 Mins extra from jan 2011.....I love EdexceL

promoters and $NF-\kappa B$, nice

WHAT ?

Gene duplication (or chromosomal duplication or gene amplification) is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination, a retrotransposition event, or duplication of an entire chromosome. The second copy of the gene is often free from selective pressure — that is, mutations of it have no deleterious effects to its host organism. Thus it accumulates mutations faster than a functional single-copy gene, over generations of organisms.

A duplication is the opposite of a deletion. Duplications arise from an event termed unequal crossing-over that occurs during meiosis between misaligned homologous chromosomes. The chance of this happening is a function of the degree of sharing of repetitive elements between two chromosomes. The product of this recombination are a duplication at the site of the exchange and a reciprocal deletion

The article is confusing when it gets to gene evolution. I feel like it is important to understand what gene duplication is and how it ties in with the specification:



So, gene duplication apparently happens as an error during meiosis. And, you get a 'spare' gene. One copy continues working normally and it free from selective pressure (does not have to evolve) and the other copy accumulates mutations faster than the functional copy and this is what evolves over time.

So a gene can give rise to more than one gene AND more than one protein.

okay correct me if i'm wrong, the old gene gets duplicated which gives a new non-functional gene, however this gene accumulates mutation over years and then when one of the functional gene stops working that gene becomes functional, and that's how a new gene is produced from another gene. (and obviously gene forms protein so the new gene will form new protein). But i don't understand how a gene can give rise to MORE THAN ONE gene??

No. ONE gene gets duplicated into TWO (or maybe more?) genes. Let's say it's two. The original gene had a function. When it is duplicated, BOTH copies are functional but only one is expressed. The other one (which is perfectly function and intact at first) just sits there and accumulates mutations and eventually becomes a new gene. So now we have two genes that are different. So we started with one gene, it was duplicated, one of the two copies evolved and now we have two genes. And from this, it is obvious that one gene gives rise to more than one protein.

But you don't have to associate the "one gene, more than one protein" concept to this article alone. Remember post-transcriptional modifications of mRNA? After transcription of a gene into premature or nascent mRNA, introns are removed and exons are spliced together (sometimes in different combinations) and this rearranges codons (hence amino acids) and you get several proteins from a single gene.