Biology- Variation, reproduction and new technology

Inheritance

• Organisms have similar charateristics to their parents
• Genes are passed in sex cells from parents to offspring
• Genes control to characteristics of your body
• The nucleus of a cell contains thread-like structures called chromosomes
• The chromosomes threads carry the genes
• In the nuclei of sex cells (gametes) there is only a single set of chromosomes
• Therefore nuclei of male and female sex cells contain one set of genes
• In most body cells the chromosomes are in pairs. One set came from the female gamete (from the mother) and one set from the male gamete (from the father)

Types of reproduction

• In asexual reproduction there is no joining of gametes
• Clones are produced by asexual reproduction
• Clones are identical copies of one parent
• Sexual reproduction involves two parents and leads to variety in the offspring
• In animals, the sex cells are eggs and sprem
• Random mixing of genes leads to variation in the offspring. This is important in survival. Some characteristics may give offspring a better chance of suriving difficult conditions

Genetic and environmental differences

• Differences in individuals of the same kind can be due to their genes, the environment or both
• Clones may have some differences due to environmental causes
• Genes are the most important factor in controlling the appearance of an individual
• Plants may be affected by lack of light, nutrients or space to grow. The weaker plants may have the same genes as the healthier plants but cannot grow well if they deprived of nutrients

Cloning

• Plant clones can be made quickly by taking cuttings from mature plants
• Tissue culture is a newer method of cloning
• Animals can be cloned by transplanting cloned embryos
• It is much more difficult to clone animals than it is it clone plants
• Cloning is used to produce new individuals that are useful in farming and agriculture
• In plants, the process of cloning can be cheap and effective. Plants can be clones by taking cuttings and growing them
• Embryo transplants are used to clone animals. In this process an embryo with unspecialised cells is split into smaller groups of cells. Each group of genetically identical cells is transplanted and allowed to develop in a host animal
• Sometimes animal or plants are genetically modified to produce useful substances before they are cloned

Adult cell cloning

• Scientists have used adult cells to clone animals such as Dolly the sheep
• The nucleus of an adult cell is transplanted into an "empty" egg cell. When the animal develops it has the genetic material of the original adult cell
• In adult cell cloning the nucleus of an adult cell, e.g. a skin cell, replaces the nucleus of an egg cell
• First the nucleus is removed from a unfertilised egg cell. The nucleus is removed from the skin cvell and placed inside the "empty" egg cell
• The new cell is given an electric shock whihc causes it to start to divide. The ball of cells is called an embryo
• The embryo is genetically identical to the adult skin cell
• One the embryo has developed into a ball of cells it is inserted into the womb of a host mother
• Dolly the sheep was produced by adult cell cloning in 1997
• Benefits of adult cell cloning:
• Development of cloned animals which have been genetically engineered to produce valuable proteins in their milk. These have uses in medicine. 

• Cloning can save animals from extinction
• Disadvantages:
• Concerns about the ethics of cloning. 
• Cloning limits the variation in a population (limits the gene pool). This can be a problem for natural selection if the environment changes
• Concerns about using the technique ti clone humans in the future

Genetic engineering

• Genetic engineerinf is used to transfer a gene from one organism to another
• Enzymes are used to "cut out" a gene from a human chromosome and then insert it into a bacterial cell
• Genes can be transferred to the cells of animals and plants at an early stage in their development
• New genes can be transferred to crop plants
• Crops with changes genes are called genetically modified (GM) crop plants.
• GM crops may be insect- or herbicide- redidtant and usually have increades yields

Making choices about technology

• There are advantages and disadvantages in the use of cloning and genetic engineering 
• The issues can be economic, social or ethical
• Advantages:
• Cloning cattle can produce heards of cattle with useful characteristics
• Adult cell cloning may be used to make copies of the best animals, e.g. race horses
• If a person has a faulty gene they may have a genetic disorder. If the correct gene can be tranferred to the person they could be cured
• Several medical drugs have been produced by genetic engineering, such as insulin and antibodies
• GM crops include ones which are resistant to herbicides or to insects
• Disadvantages
• GM crops have a bigger yield, but farmers have to buy new GM seed every year because the crops are infertile
• Some people are concerned about accidentally introducing genes into wild flower populations
• Insects which are not pests may be affected by GM crops