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GCSE Biology Summary Notes Genetics and Evolution
Summary Notes on the GCSE Biology topic Genetics and Evolution, specifically curated for the AQA Biology Exam Board.
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Genetics and EvolutionSelective Breeding
The egg and sperm are the gametes in animals.
The ovum and pollen are the gametes in plants.
Artificial insemination is injecting semen into the vagina or uterus.
A human can transfer pollen to a female plant through hands or tools.
Natural selection and selective breeding can both produces changes in animals and plants.
The difference is that natural selection occurs in nature, but selective breeding only occurs
when humans intervene. Selective breeding or artificial selection is the process by which
humans use animal breeding and plant breeding to selectively develop particular phenotypic
trait (characteristics) by choosing which typically animal or plant males and females will
sexually reproduce and have offspring together.
The desired characteristics of a dairy cow is a good milk yield and docile temperament, for a
strawberry it’s a vivid colour, large, juicy, sweet, resistant to disease and pests and a
pleasant aroma and for a pedigree dog its high fertility, good temperament and resistance
to disease.
1) Select female with best desirable feature.
2) Select male with best desirable feature.
3) Cross the best male with the best female.
4) Select the best offspring.
5) Continue breeding and select the best offspring from each generation.
6) Repeat for several generations.
Benefits:
Responsible of much of the agricultural process over the last 100 years.
More profit from desirable features
Drawbacks:
Greatly reduces number of alleles in a population which reduces variation between
individuals and characteristics, so if the climate changes or a new disease arises, there
could be mass death and the population dies out.
Inbreeding, some populations are closely bred so some are mated with close relatives,
therefore little variation so offspring are more prone to diseases or inherited defects.
More likely to pass on recessive disorders.
Reducing the gene pool, genetic variation, so can be wiped out be a new disease.
Resistant Bacteria
, There is variation in any bacterial population due to a sudden mutation some bacteria are
not affected by antibiotics, they are resistant, and not killed. If antibiotics are given, these
resistant bacteria will survive. These bacteria successfully reproduce rapidly and produce
large numbers of resistant bacteria. The resistant gene is passed onto the offspring. New
strains of bacteria are produced by natural selection.
- normal staph. Aureus are a common bacterium
- a mutation occurs that makes the bacterium resistant to methicillin
- initially the mutation has no real advantage
- if methicillin is used, the non-resistant bacteria die and the resistant bacteria have the
advantage and survive
- the methicillin resistant bacteria reproduce and pass the resistance to their offspring
becoming the dominant species
Hand gel dispensers are at the entrance of hospitals so that any resistant MRSA bacteria on
people’s hands are killed so they don’t infect patients, it prevents the transfer.
Overusing antibiotics might speed up the development of resistant strains of bacteria.
Genetic Engineering
Genetic engineering involves modifying the genetic material of an organism. The gene for a
desirable characteristic is cut out of one organism and transferred to the genetic material in
the cells of an organism. This gives the genetically engineered organism a new desirable
characteristic.
1) Cut required gene out of chromosome using enzymes.
2) Cut open the bacterial plasmid using the same enzymes.
3) Use a different enzyme, ligase, to join the gene with the plasmid.
4) Put recombinant plasmids back into the bacterial cell.
5) Bacterial cell will clone via mitosis to many identical copies.
It can be used to treat diabetic patients.
A vector is something that carries something into a cell/ host.
Bacteria reproduce rapidly and via mitosis, so they are clones, identical genetic information.
If a plant, cut open the chromosome using the same enzyme and insert the gene into the
DNA of the cells to be modified.
We always check it’s taken to the resistance gene. It kills any cells that doesn’t have the
gene, so only GM cells should survive, and hence all will contain the desired gene.
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