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the nucleus of a cell contains thread-like structures called chromosomes

chromosome threads carrys genes

in gametes there is only one set of chromosones

genes are passed in sex cells from parents to offspring (during repoduction)

offspring cells contain two sets of genes inherited from parents

genes control the charactertics of your body

Asexual reptoduction does not involve the fusion of gametes 

all genetic information comes from one parent (little variety)

identical copies produced by asexual repoduction are called clones

Sexual repoduction involves the fusion of sex cells there is a mixture of genetic information so offspring shows variation

cannot be identical because its a combination of 2sets of genes

differences in individuals of the same kind can be due to their genes the environment or both

-inherited

-developed

-a combination of both these genetic and environmental causes

genes most important factor in controlling the appearance of an indivaul

plants may be effected by lack of light,nutrients of space to grow

if mother smokes or drinks a lot baby may have a small birth weight

once animals are born too much or too little food can alter their characteristics

more difficult to clone animals than to clone plants

used to produce new indivuals that are useful in farming and agriculture

the process of cloning can be cheap and effective

plants can be cloned by taking cuttings and growing them

taking small groups of cells from part of a plant and growing under special conditions (tissue culture) is more expensive (but used to reproduce large numbers of rare or top quality plant)

embryo transplants are used to clone animals

in this process an embryo with unspecialised cells is split into smaller group cells

sometimes animals or plants are genetically modified to produce useful substances before they are cloned

the nucleus e.g. skincell ,replaces the nucleus of an egg cell

first the nucleus is removed from an unfertiised egg cell

nucleus is removed from the skin cell an placed inside the 'empty' egg cell

new cell is given an electrical shock which causes it to start to divide 

the ball of cells is called an embryo

embryo is genetically indentical to the adult skin cell

once it has developed into a ball it is placed into the womb

dolly the sheep was the first produced by adult cell cloning in 1997

befits:

save animals from extintion

uses in medicine

disadvantages:

ethnic concerns

concerns using the technique to clone humans in the future

involves changing the genetic make-up of an organism 

genetic engineering is used to transfer a gene from one organism to another

enzymes are used to cute out a gene from a human chromosome and then insert it into a bacteria cell

genes can be transferred to the cells of animals and plants at an early stage in their development 

there are many advantages but also disadvantages in using cloning and genetic engineering

advantages:

cloning cattle can produce herds of cattle with useful characteristics

best animals e.g race horses

if a person has a genetic disorder (faulty gene) if the correct gene can be transferred the person will then be cured

disadvantages:

GM bigger yield but farmers have to buy new GM seed every year because the crops are infertile

insects are not pests may be effected by the crops 

began 3billion years ago

lamarck suggested "the inheritance of acquired characteristics"

that characteristics which develop during organisms lifetime can be passed on to the next generation

e.g, if two parents were build up their muscles in the gym Lamarks theory would predict that this characteristic would be passed on to their offspring

charles darwin:

"natural selection"

small changes in organisms took place over a very long time.

accepted:

-challanged the theory of god,made all the animals and plants that lived on earth

-many scientists where not convinced because they still did not think there was sufficient evidence for theory

darwin could not explain about why there is a varity of organisms or how inheritance worked

they didnt kn about genes until 50years later

Most organisms produce large number of offspring

individual organisms will show a wide range of variation because of differences in their genes

all the organisms in the population will compete for food, shelter from predators and mates

the organisms with the characteristics most suited to the environment will survive 

-best camouflage

-best eyesight to find food

-strongest to builld a burrow 

-the quickest to run from a predator

organisms which survive are more ikley to breed successfully

sometimes a gene accidentally changes and becomes a new form of the gene (mutation)

if mutated gene controls better characteristic which makes the organism better adapted to the environment then it will be passed on to the offspring

putting organisms into groups into groups we can make more sense of how closely they are related

grouping organisms is called classification

natural classification system  is used to study the similarities and differences between organisms in order to classify them

the largest groups are called kingdoms 

main kingdoms:

-plant kingdom

-animal kingdom

-the kingdom which contains the microorganisms

the smallest group in the classification system is the species 

evolutionary trees are models that can be drawn to show the relationships between different groups of organisms

when new evidence is found,they may modify these evolutionary relationships

ecological relationships tell us how species have evolved together in an enviroment