Environmental variation + Genetic variation 

What can cause differences in the characteristics of an individual population? (2)

If 2 alleles are different, only 1 can determine what characteristic is present - this is the dominant allele 

Both alleles are needed for the characteristic to be present 

How many chromosomes does the human body contain?

Dominant allele / extra fingers & toes / not life threatening / parent will have condition too as it is dominant 

Recessive / Disorder of cell membrane / thick sticky mucus in air passages & pancreas / people with 1 copy of allele are carriers / for child to have disorder, both parents must be carriers  

All of today’s species have evolved from simple life forms that first started to develop over 3 billion years ago 

Organisms with the most suitable characteristics for the environment would be more successful competitors/ would be more likely to survive & pass on the genes for those characteristics. The beneficial characteristics will become more common, resulting in evolution 

Explain how evolution occurs through natural selection 

A group of living organisms of similar genes that are able to reproduce 

Speciation: Phenotypes change so much overtime that a new species forms (when population changes enough to be reproductively isolated) 

The transfer of genes between organisms. (Transfer gene responsible for desired characteristic from one organism’s genome to another so it also has the desired characteristic)

Disease resistance / to produce bigger fruits / better quality / insect & herbicide resistance

Why have most plant crops been genetically engineered?

Useful gene is (cut) / isolated from an organism’s genome using enzymes and inserted into a vector (a viral or bacterial plasmid). The vector is introduced to target organism - useful gene is inserted into its cells 

Describe the main steps of genetic engineering 

Bacteria modified to produce human insulin / GM crops (better yield & develop resistance) / sheep (produce substances like drugs in their milk to treat human diseases) / gene therapy 

Describe the uses of genetic engineering 

Why have bacterial cells been genetically modified?

Some say growing GM crops will affect the number of wildflowers & population of insects, reducing farmland biodiversity / people think it’s not safe / people think they may develop allergies / transplanted genes may get into the natural environment (e.g: herbicide resistance may create “super weeds”) 

Why don’t some people agree with genetic engineering in agriculture/ medicine? 

(used to preserve rare plants): A few plant cells are put into a growth medium with hormones. They grow into new plants (& are clones of parent plants). They’re made very quickly in a very little space & can grow all year 

Sperm cells taken from prize bull. Artificially fertilise egg. Embryo developed is split many times to form clones before any cell becomes specialised. Cloned embryos are implanted into lots of cows. They grow into baby calves (which are all genetically identical) - hundred ms of ideal offspring produced

Describe the process of embryo transplants 

Remove nucleus of unfertilised egg. Remove nucleus of adult body cell and insert that into the egg. Egg cell stimulated by electric shock which makes it divide like a normal embryo. When it’s a ball of cells, is implanted into the womb of an adult female. It grows into a clone of the original adult body cell as it has the same genetic information. 

Describe the process of adult cell cloning 

Relevant scientific knowledge wasn’t available at the time - no good explanation why new characteristics appeared or how exactly the adaptations were passed on. (but now we know about genes/mutations:)

Explain why Darwin’s theory of evolution was only gradually accepted 

He thought the changes an organism acquired through its lifetime would be passed onto its offspring. (but we know that it can only pass genes not characteristics) Experimenrs didn’t support his hypothesis so his idea was rejected.

Warning colours are used by some species to deter predators from eating them (this is an example of beneficial characteristic that had evolved by natural selection) 

Describe the work of Alfred Russel Wallace on warning colouration of animals 

Organisms with better characteristics suited to environment = more likely to survive & breed = gene for those characteristics passed on = survival of fittest = evolution 

Describe Darwin’s theory of evolution by natural selection? 

Each population shows genetic variation because they have a wide range of alleles. In each population, individuals with characteristics that make them more suited for the environment make them better for survival = breed successfully. The alleles that control beneficial characteristic are more likely to be passed on to the next generation. Eventually, they’ll change so much, they’ll form new species.

Describe Wallace’s theory of speciation

1 parent cell splits into 2 daughter cells / same # of chromosomes (diploid) / genetically identical cells / for growth & repair 

1 parent cell splits to make 2 daughter cells and then they split again to form 4 daughter cells in total / half the # of chromosomes (haploid) / non identical cells / for production of sex cells 

How does sexual reproduction result in genetic variation? 

Population can increase rapidly in favourable conditions/ only 1 parent is needed so more time & energy efficient / faster than sexual reproduction 

No variation / may be suited to only 1 habitat / disease may affect all individuals in a population 

Cell duplicates genetic information forming 2 armed chromosomes. 1 division: chromosome pairs line up in middle of cell. Pairs are pulled apart so each new cell has 1 copy of each chromosome. 2nd division: Chromosomes line up again- arms pulled apart. This results in 4 gametes, each with a single set of chromosomes. (each is genetically different)

How do cells in reproductive organs divide by meiosis to form gametes?

Variation - so species can adapt to new environments = survival advantage / disease less likely to affect all / humans can speed up natural selection through selective breeding = increased food production 

Time and energy needed to find a mate / Not possible for an isolated individual 

They release spores which can become new fungi when they land in a suitable space. Asexually produced spires are genetically identical to parent fungus. Sexually reproduced spores are often produced in response to unfavourable conditions and can increase chance that population will survive the change. 

Describe how fungi are able to reproduce 

When a mosquito carrying the parasite bites a human, the parasite is transferred to the human. Parasite reproduces sexually when it’s in the mosquito and asexually when it’s in the human host.  

Describe how malarial parasites are able to reproduce 

New bulbs can form from the main bulb and divide off. Each new bulb can grow into a new identical plant 

How are strawberry plants able to reproduce?

DNA strands are polymers. DNA is shaped as a double helix. It is made up of nucleotides which contain: deoxybrose sugar/ phosphate group/ a base  

Each base links to base on opposite strand in helix (A&T and C&G) The order of bases deducted order of amino acids. Amino acids join together to make proteins depending on the order of bases. Wrong sequence = wrong protein made  

Explain the importance of the sequence of bases of DNA 

DNA unzips. mRNA builds up in a pattern exactly replicating DNA’s sequence (this is called transcription) mRNA moves out of nucleus through the pores in the cell membrane (this is called translation). tRNA/carrier molecule binds to corresponding amino acids at one end. At other end, shaped to fit codon. (A codon is 3 bases) Enzymes link amino acids together, forming a new polypeptide chain. This chain folds into a protein and voíla. 

Wrong bases = wrong mRNA replicated = wrong amino acids formed = produces an entirely different protein to what it was supposed to be 

How can a change in DNA structure result in a change in the protein synthesised? 

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