GCSE Core Biology Revision 2

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VARIATION, REPRODUCTION AND NEW TECHNOLOGY

INHERITANCE

your characteristics are inherited from your parents

Youre resemblance to you parents is the result of information carried by genes. These are passed on to you in the sex cells (gametes) from which you were developed

Genetic information is carried in the nucleus of cells, passed on during reproduction- inside nucleus are thread-like structures called chromosomes. The chromosomes are made up of a special chemical called DNA (where genetic information is stored). DNA is a long molecule made up of two strands that are twisted together in a double helix structure

Each different type of organism has a different number of chromosomes in its body cells. Humans have 46, turkeys have 82.

Inherit half your chromosomes from your mother, and half from your father so chromosomes come in pairs

each of your chromosomes contain thousands of genes joined together- each gene is a small section of the long DNA molecule Genes control all characteristics

chromosomes are organised so that both of the chromosomes in a pair carry genes controlling the same things- so genes come in pairs

some characteristics decided by a single pair of genes- others by different genes working together

each chromosome in a pair carries genes which code for the same characteristic

TYPES OF REPRODUCTION

ASEXUAL- involves one parent- no variety- genetically identical offspring (clones)- plants- also cells of your body reproduce asexually all the time for growth and replacement

SEXUAL- involves male and female gametes from two parents, join together- genetic information is combined so introduces variety- genetic variation

genetic variation is a great advantage for survival. Variety makes it more likely that a few of the offspring will have the ability to survive difficult conditions

GENETIC AND ENVIRONMENTAL DIFFERENCES

nature- genetic variety- the genes you inherit- determine basic characteristics

nurture- environmental variety

differences between individuals caused by both genes and environment

CLONING

individual produced asexually and is genetically identical to the parent

gardeners produce new plants by taking cuttings from older plants (remove a small piece of the plant and put in the right conditions for shoots and roots to form) produces new plants cheaply and quickly from old plants, will be genetically identical- many growers now use hormone rooting powders to encourage cuttings to grow. Produce plants such as orchids commercially by cloning in this way

Tissue culture- more expensive but allows you to make thousands of new plants from one tiny piece of plant tissue, use a mixture of plant hormones to make a small group of cells from the plant you want to clone to produce a big mass of identical plant cells, then (using mix of hormones and optimum conditions) stimulate each of these cells into a new plant

Cloning animals- quite common in farming- using embryo cloning best cows can produce many more top-quality calves each year- give an animal fertility hormones so that it produces lots of eggs- fertilise these eggs with chosen sperm- sometimes done inside the cow then embryos washed out or done in the lab. Each embryo is then divided into several individual cells (unspecialized still), each cell grows into an identical embryo in the lab, transfer embryos to host mothers who have been given hormones), identical cloned calves are then born

Embryo cloning is skilled and expensive work but profitable. high quality embryos can be carried to places where cattle with a high milk yield orlots of meat are badly needed for breeding

Also used to make lots of identical copies of embryos that have been genetically modified to produce medically useful compounds

ADULT CELL CLONING

form of asexual reproduction- cloning- difficult technique- nucleus is removed from an unfertilised egg cell, at the sametime the nucleus is taken from an adult body cell (eg a skin cell), the nucleus from the adult cell is inserted into the empty ovum, the new cell is given a tiny electric shock that makes it start dividing to form embryo cells (contain sae genetic information as the original adult cell and original adult animal), when the embryo has developed into a ball of cells it is inserted into the womb of an adult female

first example of adult cell cloning- Dolly the sheep 1997

technique still difficult and unreliable

benefits- can produce clones of genetically engineered animals- medically useful, could save animals from extinction or even bring back species that died out years ago, cloning pets

disads- could lead to cloning human babies for infertile couples- could be abused, reduces variety in population so pop is less able to survive any changes in the environment that might happen in the future, unethical human cloning?

GENETIC ENGINEERING

changing the genetic material of an organism, genes from the chromosomes of a human cell can be cut out using enzymes and transferred to the cell of a bacterium- gene carries on making a human protein despite being in a bacterium

cut out an insulin gene of some human DNA using an enzyme, take out a plasmid (ring of DNA) out of bacterium and split it open using an enzyme, insert the insulin gene into the plasmid using another enzyme, the plasmid with the insulin gene is then taken up by the bacterium and multiplies, produces insulin which is harvested

Genetically engineered bacteria cultured on a large scale make huge quantities of protein from other organisms- medical use

Scientists have moved on from bacteria to genetically engineered animals and plants

benefits- make proteins we need, in exactly the right amounts needed and in a very pure form (human insulin from GE bacteria for people with diabetes instead of animal insulin used in the past), can improve the growth rates of plants and animals, GM crops have bigger yields than ordinary crops, can be designed to grow well in dry hot parts of the world (solve world hunger), crops can be engineered to make their own pesticides or resistance to herbicides

human engineering- could solve problem of genetic diseases- implant healthy genes into affected cells so work properly

disads- very new, long term effects unclear, may affect food chains and ecosystems, affect of eating GM food on human health, genes from GM plants might spread into the wildlife of the countryside, GM crops often infertile so farmers must buy new seed each year, ethical issues of manipulating human genes and characteristics

MAKING CHOICES ABOUT TECHNOLOGY

cloning pets- waste of time and money and unethical? could give a home to millions of unwanted animals, not worth it for the many attempts needed to get the process to work

GM foods- ads and disads

EVOLUTION

THEORIES OF EVOLUTION

theory of evolution- all living things alive today have evolved from the first simple life forms more than 3 billion years ago- relatively new idea

Jean-Baptiste Lamarck- idea that every type of animal evolved from primitive worms- change of worms to other organisms was caused by the inheritance of acquired characteristics, he believed the way organisms behaved affected the features of their body, useful changes would be passed to the offspring

Lamarck's theory influenced Charles Darwin. However no evidence for 'fountain of life' and people didnt like the idea of being descended from worms. not all changes passed on to children- in great majority of cases Lamarck's idea couldnt happen

Charles Darwin- Galapagos Islands- theory of evolution by natural selection is that all living organisms evolved from simpler life forms- evolution came about by natural selection- reproduction always gives more offspring than the environment can support, those that have inherited features most suited to their environment will survive. When they breed, they pass on the genes for those useful inherited characteristics to their offspring

Darwin didn't know about genes, just called them useful inherited characteristics

ACCEPTING DARWIN'S IDEAS

Darwin tried to build up lots of evidence as he knew there would be lots of opposition from scientists and religious leaders.

objection due to challenging in the belief of God, still not enough evidence and no-one knew about genes or genetics so no mechanism for explaining variety and inheritance

NATURAL SELECTION

only the offspring with the genes best suited to their habitat manage to stay alive and breed succesfully

new forms of genes result from changes in existing genes- these changes are known as mutations (tiny changes in the long strands of DNA), occur naturally through mistakes made in copying DNA when the cells divide, introduce more variety into the genes of a species

some mutations have no effect and some are harmful

if mutation helps an organism survive and reproduce it will get passed on to the next generation, mutant gene will gradually become more common in the population, it will cause the species to evolve

when new forms of gene arise from mutation, there may be a more rapid change in a species

CLASSIFICATION AND EVOLUTION

classification is the organisation of living things into groups- makes it easier to study organisms- allows us to make sense of the living world and understand how life began and how different groups of living things are related to each other.

System we use is the natural classification system- biggest groups are the kingdoms (animal and plant), micro-organisms are then split between three different kingdoms

kingdoms contain lots of organisms with many differences but a few important similarities.

The smallest group is a species- members of the same species are very similar, differences are small variations of the same feature. A species is a group of organisms that can breed together and produce fertile offspring

Scientists have developed models to show the evolutionary links between different organisms, called evolutionary trees

scientists are increasingly using DNA evidence as well as observation to decide what species an animal belongs to. Look for differences and similarities in DNA which allow them to work out the evolutionary relationships between organisms. Can also see how long ago different organisms had a common ancestor

how species have evolved together in an environment is their ecological relationship and another model

ecological and evolutionary models and relationships

variation, reproduction and new technology

evolution