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

1. (Original post by buyingtheticket)
Will these just be the epistasis ratios ( as in the ones we have to learn)?
Maybe. But I think the ratio would probably be given in the question for the expected result, and a population size would also be given, you would have to calculate the expected result in terms of the population.
2. (Original post by xXxBaby-BooxXx)
Genetic Drift - Random fluctuations in the frequency of the appearance of a gene in a small isolated population, presumably owing to chance rather than natural selection. The effect is almost negligible in a large population.

I can't think what you mean by the other one Remember the word and I might be able to help :P
Oh no! I learnt something completely different for genetic drift

That genetic drift occurs when there is a change in allele frequency due to natural selection (and selection pressures).
**** why are my teachers so ****
3. (Original post by lekky)
Oh no! I learnt something completely different for genetic drift

That genetic drift occurs when there is a change in allele frequency due to natural selection (and selection pressures).
**** why are my teachers so ****
Well that's what it said on answers/wikipedia :P

My textbook says:

Also called allelic drift. The change in allele frequency in a population, as some alleles pass to the next generation and some disappear. This causes some phenotypic traits to become rarer or more common.

AND

Fluctuation or changes in allele frequency is called genetic drift.
4. I learnt genetic drift as being a change in allele frequencies that occurs randomly by chance.
5. (Original post by student92)
Maybe. But I think the ratio would probably be given in the question for the expected result, and a population size would also be given, you would have to calculate the expected result in terms of the population.
Or you could make up the ratio by cross linking gametes or a punnet square.
6. (Original post by student92)
I learnt genetic drift as being a change in allele frequencies that occurs randomly by chance.
yep random is the word.
7. (Original post by xXxBaby-BooxXx)
Well that's what it said on answers/wikipedia :P

My textbook says:

Also called allelic drift. The change in allele frequency in a population, as some alleles pass to the next generation and some disappear. This causes some phenotypic traits to become rarer or more common.

AND

Fluctuation or changes in allele frequency is called genetic drift.
That's what I said..
8. (Original post by lekky)
That's what I said..
Well you said it's down to natural selection/selection pressures, whereas its more down to chance with egg and sperm meeting, and there's no way to select an egg with a specific allele in it for example, so by chance it won't appear in the offspring.
9. (Original post by xXxBaby-BooxXx)
Well you said it's down to natural selection/selection pressures, whereas its more down to chance with egg and sperm meeting, and there's no way to select an egg with a specific allele in it for example, so by chance it won't appear in the offspring.
no but an offspring with a favourable allele is more like to survive and reproduce, passing that allele onto their offspring and over generations the allele frequency will increase

offspring without the favourable allele are more likely to die and not reproduce, so allele frequency will decline and eventually be lost.

Meh I'm confused. How exactly is it down to chance?
10. (Original post by lekky)
no but an offspring with a favourable allele is more like to survive and reproduce, passing that allele onto their offspring and over generations the allele frequency will increase

offspring without the favourable allele are more likely to die and not reproduce, so allele frequency will decline and eventually be lost.

Meh I'm confused. How exactly is it down to chance?
You are right ones with favorable alleles survive but as in the case with haempohilia (no females ).. there are various other factors in case of genetic drift. well it is random/spontaneous(Occurs only when there is no selection pressure!).Also genetic drift could lead to loss of variety(gene pool).Then again i read somewhere that overtime genetic uniformity takes place even though (meiosis) occurs.
Err bottom line is: Differences /variation occur due to natural selection and genetic drift which are different approaches to evolution.
11. Stabilising selection: Successive appearance of a particular allele in each generation due to stable conditions.
Directional selection: Gain/loss of an allele/alleles due to selection pressure on the population.
12. Tissue Culture: Is the cloning of plants done at industrial scale.The process starts off by first collecting 'callus'.Callus are irrgular mass/bundle of cells which form whenever a plant is wounded(mitosis).Not all cells are able to reproduce but ones which are able to are called 'meristematic cells'.These cells are removed and named explant.The explant is then transfered into aerated solution/mixture of plant growth substances(regulators) such as auxins,gibberrlins and cytokinin all is done under sterile condition( since callus is at a premature state = pathogen attack = r.i.p).
Different concentration of plant growth substances are added depending on the plant specie,growth phase.All this is done by trial-error.They differentiate into root,stem.
13. Hey guys im back took a long break off biology but ive managed to cover genetics and cellular control made notes etc.
Im finding it hard to learn genetics directly from the book its just so complicated especially epistatis.
As long as everyone works hard from today theres plenty of time even if you havent started.
14. On the book by Mary jones there isnt much given about reproductive cloning hardly a para. on its disadvantage
All i could gather from it is: Reproductive cloning is the formation of a whole organism by the fusion of a cell with eunucleated egg = zygote.
15. (Original post by MG.GULED)
Hey guys im back took a long break off biology but ive managed to cover genetics and cellular control made notes etc.
Im finding it hard to learn genetics directly from the book its just so complicated especially epistatis.
As long as everyone works hard from today theres plenty of time even if you havent started.
Hey! nice to have you back
here post i made last night:
hought of making down notes as i whiz through
OK
First er not to confuse Co-dominance with Epistasis.In Co-dominance both alleles show their phenotype(none masked) (example blood group)while epistasis is the control of one particular phenotype by two or more genes.For example take ratatouille
Allele BB/Bb = codes for an enzyme to convert tyrosine to melanin and allele b for no enzyme (an albino).
And Allele A produces enzyme TYRP1(varies quantity of melanin) which depending on allele type produces either agouti or black color coat.
Allele: aa = black and alleles AA/Aa = agouti.
Epistatic allele: B
Hypostatic allele:A
Ask if you got any questions.
16. Continous and Discontinous variation

Continuous
- Quantitative
- many genes - polygenic
- Genes have the same effect
- Different alleles on each gene locus have a small effect on the phenotype
- Large effect on environment
- Frequency histogram
e.g. - Length of fungi, length of a root, mass of an animal.

Discontinuous
- Qualitative
- few or often 1 gene - monogenic
- Genes have different effects
- Different alleles on a single gene locus have a large effect on the phenotype
- Small effect on environment
- Bar chart
e.g. - Antibiotic resistant, Flower colour, ABO.

Genotype and environment contribute to the phenotype
- Genotype - inherited.
- Environmental - not inherited
- results from different environmental experiences
during an individuals lifetime.
P = G + E

Variation
- Individuals who are well adapted will survive and reproduce.
- Pass on advantageous alleles to offspring.
- Based on natural selection.
- Provides 'raw materials' for selection.
17. (Original post by student92)
I learnt genetic drift as being a change in allele frequencies that occurs randomly by chance.
what is the difference between genetic drift and mutation?
18. (Original post by ibysaiyan)
Stabilising selection: Successive appearance of a particular allele in each generation due to stable conditions.
Directional selection: Gain/loss of an allele/alleles due to selection pressure on the population.
is the environment a factor to changes in allele?
19. (Original post by student92)
Continous and Discontinous variation

Continuous
- Quantitative
- many genes - polygenic
- Genes have the same effect
- Different alleles on each gene locus have a small effect on the phenotype
- Large effect on environment
- Frequency histogram
e.g. - Length of fungi, length of a root, mass of an animal.

Discontinuous
- Qualitative
- few or often 1 gene - monogenic
- Genes have different effects
- Different alleles on a single gene locus have a large effect on the phenotype
- Small effect on environment
- Bar chart
e.g. - Antibiotic resistant, Flower colour, ABO.

Genotype and environment contribute to the phenotype
- Genotype - inherited.
- Environmental - not inherited
- results from different environmental experiences
during an individuals lifetime.
P = G + E

Variation
- Individuals who are well adapted will survive and reproduce.
- Pass on advantageous alleles to offspring.
- Based on natrural selection.
- Provides 'raw materials' for selection.
Thnx buddy! SO useful.
20. (Original post by Remarqable M)
what is the difference between genetic drift and mutation?
A mutation is a change in nucleotide base sequence within a DNA strand. Genetic drift is a change in allele frequencies, so a mutation actually takes place inside the gene, genetic drift is talking about the overall picture.

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