Monday, 20 May 2013

3.33 understand that the incidence of mutations can be increased by exposure to ionising radiation (for example gamma rays, X-rays and ultraviolet rays) and some chemical mutagens (for example chemicals in tobacco).

There are things that make you more likely to have a mutated gene, these include: ionising radiation and chemical mutagens like some chemicals in tobacco.

3.32 understand that resistance to antibiotics can increase in bacterial populations, and appreciate how such an increase can lead to infections being difficult to control

Bacteria experience mutations (the reproduce very frequently so it is not rare.) These mutations can mean that they are no longer affected by a certain antibiotic, this makes it easier for them to survive. If bacteria evolve to be resistant to drugs we are treating them with then they are difficult to control; sometimes they can be stopped using a different antibiotic, but some are becoming resistant to all the drugs that we know of...

3.31 understand that many mutations are harmful but some are neutral and a few are beneficial

A lot of mutations are harmful, like genetic diseases; cystic fibrosis.
Some don't change the chances of survival: like having a different colour hair.
There are a few mutations which are beneficial, for example a insect pollinated plant becoming brighter.

3.30 describe the process of evolution by means of natural selection

Evolution is a change in species over a very long time (sometimes into different species.)
Natural selection is survival of the fittest.
What happens is:

  • A mutation occurs
  • If the mutation is beneficial, the animal will survive longer and reproduce more
  • Some of its offspring will inherit the mutation
  • These offspring will also have better chance of survival, meaning they live longer and reproduce more
  • Over a long period of time this process is repeated and gradually the mutation becomes a common gene in a species and those with the mutation become the only ones, as those without cannot compete with those expressing the mutated gene

3.29 understand that mutation is a rare, random change in genetic material that can be inherited

A mutation is when a gene is copied incorrectly, this gene can be passed down. It doesn't happen very often or on purpose.

3.28 understand that variation within a species can be genetic, environmental, or a combination of both

Variation in a species is the differences between the members of a species.
Genetic is caused by what genes are inhereted.
Environmental is caused by some action after birth (e.g the sun giving you a tan.)
Some variation is a bit of both...

3.27 know that in human cells the diploid number of chromosomes is 46 and the haploid number is 23

The diploid number is how many chromosomes each cell is meant to have: 46 in humans (23 pairs).
The haploid number is half of the diploid number: so 23.

3.26 understand that random fertilisation produces genetic variation of offspring

Because gametes contain a random selection of genetic information from each parent, the fertilised egg will be a mix of different genotypes which is why offspring are genetically different to their parents.

3.25 understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes

Meiosis is when a cell splits in half, creating two copies, and then splits in half again to create four cells each with half the genetic information of a normal cell (haploid 23 chromosomes.)
This is how gametes are made.

3.24 understand that mitosis occurs during growth, repair, cloning and asexual reproduction

Mitosis cell division is the type that occurs in growth, repair cloning and asexual reproduction.

3.23 understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes

Mitosis is when a cell replicates it self to make an identical copy.
A diploid cell is one with 23 pairs of chromosomes.
(you don't need to know the stage names, but its useful to know how mitosis happens.)


3.22 describe the determination of the sex of offspring at fertilisation, using a genetic diagram

Genetic diagrams work the same as mono-hybrid inheritance diagrams: showing the mothers and fathers and then the different out comes. The only difference is, they will always be the same because one parent is always male and one parent is always female:
Gender determination

3.21 understand that the sex of a person is controlled by one pair of chromosomes, XX in a female and XY in a male

One pair of chromosomes (out of 23 pairs) controls the gender of a person. XX is female; XY is male.

3.20 predict probabilities of outcomes from monohybrid crosses

From mono-hybrid cross diagrams there are four outcomes, some times some of the out comes are the same.
To work out the probability of a child inheriting a genotype, you see how many times it comes up and divide it by 4 then times by 100 for a percent.
To work out phenotype probability you work out how many times they will express a characteristic and divide it by four then times by 100 for a percent.

If we say in this diagram the B represents brown hair and b represents red hair
(The capital letter is always dominant)


The likely hood of the chlid carrying one allele for brown and one for red (Bb) is two out of four:
2/4= 0.5
x100= 50%
The likely hood of the child having red hair (red hair is recessive so they both have to be red (bb)) is two out of four: also 50%

3.19 understand how to interpret family pedigrees

A pedigree diagram shows a specific gene in a family. It will have a key but most often: a circle represents a female and a square represents a male; often coloured in represents one allele and blank another (but sometimes they are different colours.)

In this diagram, the mother and two sons have a different genes to the others:


3.18 describe patterns of monohybrid inheritance using a genetic diagram

Monohybrid inheritance is the inheritance of one gene.
A genetic diagram consists of the parents gamets (according to their genotype) and their possible offspring:
(B and b represent an allele for a gene)

3.17 understand the meaning of the terms: dominant, recessive, homozygous, heterozygous, phenotype, genotype and codominance

Dominant: a dominant allele is the one that will be made
Recessive: a recessive allele will be masked by a dominant one and not visible
Homozygous: if you have two of the same alleles for a gene in one persons DNA
Heterozygous: if you have two different alleles for a gene in in someones DNA
Phenotype: what allele is expressed as a protein
Genotype: what alleles you have in your DNA for a gene
Codominance: when two alleles have equal dominance (they will both be expressed)

By expressed I mean shown as in having brown hair is brown hair allele being expressed; and by masked I mean not expressed.

3.16 understand that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics

Genes (sections of DNA coding for different proteins) come in a variety of forms: for example the gene that codes for hair can come in many different colours. These different forms are different alleles, having these differences is where you vary in inherited characteristics (If there was only one allele for hair we would all have exactly the same hair.)

3.15 describe a DNA molecule as two strands coiled to form a double helix, the strands being linked by a series of paired bases: adenine (A) with thymine (T), and cytosine (C) with guanine (G)

DNA resembles a ladder (that has been twisted,) on either side of each rung will be a base- they are a base pair: either adenine (A) with thymine (T) or cytosine (C) with guanine (G).

3.14 understand that a gene is a section of a molecule of DNA and that a gene codes for a specific protein

Different genes code different proteins. Genes are sections of your DNA.

3.13 understand that the nucleus of a cell contains chromosomes on which genes are located

In the nucleus of a cell there are chromosomes; these are long sections of tangled DNA, sections of which are different genes.

Friday, 17 May 2013


Finished. I have now posted notes on every point on the spec!
Hope it helps,
Good luck!!!

5.20 evaluate the potential for using cloned transgenic animals, for example to produce commercial quantities of human antibodies or organs for transplantation.

Transgenic animals are ones that have had genes from other animals put in their DNA.
Animals can be given the gene to make human antibodies. These can then be injected into humans to help them face an infection- instead of waiting a long time for their body to find the correct antibody and then replicate it.
Sheep and goats have been made to produce human proteins in their milk: this makes milk more beneficial to humans.
Animals could be made with organs that are similar enough to humans that they could be transplanted: this would mean there was never a shortage; it would also mean less moral questions are asked (then using human organs.)

4.15 understand the biological consequences of pollution of water by sewage, including increases in the number of micro-organisms causing depletion of oxygen

Sewage contains nutrient which enable algae to flourish. They take up sunlight and oxygen. Many fish die and other organisms die. Decomposers thrive on there dead bodies; meaning even more oxygen is taken up by microorganisms.

Basically its the same process as eutrophication.

5.13 describe how plasmids and viruses can act as vectors, which take up pieces of DNA, then insert this recombinant DNA into other cells

When a virus or plasmid is inside a host cell it may pick up DNA, it may then carry this into another host cell. The foreign DNA is known as recombinant DNA.

Wednesday, 15 May 2013

5.19 describe the stages in the production of cloned mammals involving the introduction of a diploid nucleus from a mature cell into an enucleated egg cell, illustrated by Dolly the sheep

A egg cell with the nucleus removed has the DNA of another cell put in (this will be have a complete set of chromosones (diploid number of)). The embryo that forms will then have DNA from only one parent: the one the DNA was taken from. This means it will be a clone! for example dolly the sheep.

Inline images 1

5.18 understand how micropropagation can be used to produce commercial quantities of identical plants (clones) with desirable characteristics

In micropropagation, plant clippings are taken and put in a growth medium. They will develop into a new plant with the same DNA. This means that every plant made from the clippings of one plant will be clones with exactly the same characteristics. If many clippings are taken then you will have many clones.

5.17 describe the process of micropropagation (tissue culture) in which small pieces of plants (explants) are grown in vitro using nutrient media

Plant clippings are taken and placed in a sterile growth medium. Roots will develop from the clipping (and shoots) making a whole new plant. The plant will then be transferred into compost and grown as a normal plant.
The plant is a clone of the one is was taken from because it has the same DNA. This means that there will be no variation, so you can have the same plant every time.

5.16 understand that the term ‘transgenic’ means the transfer of genetic material from one species to a different species

transgenic material is genetic material that is taken from one species and put into another.

5.15 evaluate the potential for using genetically modified plants to improve food production (illustrated by plants with improved resistance to pests)

Genetically modified plants are ones with desired characteristics which are meant to enhance a crop.

They may have DNA which gives them more nutritional value: like golden rice which is rice with carotene in. This will benefit a population which eats a lot of rice by giving them a better diet.

Plants may also have DNA which makes them more resistant: for example genetically modified soya plants. This means that a broad spectrum herbicide that kills many different types of plant can be spread on the crops to kill weeds; where as before many different types of herbicides would have to be spread to avoid killing the crop (time consuming/ expensive.)

Although GM plants appear to be only of benefit, there are people who claim side effects observed in lab animals such as: sterility; infant mortality; allergies; stunted growth. Another disadvantage would be that a broad spectrum herbicide that can be spread on GM crops will kill many plants in the wild not just the weeds  threatening the crops.

5.14 understand that large amounts of human insulin can be manufactured from genetically modified bacteria that are grown in a fermenter

The gene that causes human insulin production is taken from a cell and put into a bacteria's DNA. This bacteria is then put into a fermenter where the conditions are optimum for it to replicate many times. These bacteria then produce human insulin which can be harvested and given to humans with diabetes.

This is a very helpful animation:

5.12 describe the use of restriction enzymes to cut DNA at specific sites and ligase enzymes to join pieces of DNA together

Restriction enzymes effectively cut through DNA strands so that a section of DNA can be taken from a cell.

Ligase enzymes can be used to join together different sections of DNA.

These processes are done to create new DNA.

Something like this:


5.6 describe a simple experiment to investigate carbon dioxide production by yeast, in different conditions

Have a test tube of yeast in glucose solution. Put a layer of oil on top if you want the yeast to respire anaerobically (as it will prevent oxygen entering the solution.)

Put the test tube in a water bath, heat the water to vary the temperature.

Collect gas coming off in a tube then: count the bubbles; use downwards displacement.

5.11 understand that animals with desired characteristics can be developed by selective breeding

Farmers can choose to make sure animals with characteristics they desire reproduce, their offspring will inherit the genes of the characteristic.

5.10 understand that plants with desired characteristics can be developed by selective breeding

Farmers can breed plants selectively  choosing plants with characteristics they desire (eg colour, size of fruit) to pollinate.