B1:6

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(6.1) Chromosomes and genes

Genetic information is carried in chromosomes in the nucleus and passed on through sexual reproduction in the gametes.

Chromosomes are made of DNA

DNA has a double helix structure

Humans have 46 chromosomes

These are in 23 pairs - half from the father and half from the mother

Genes are the basic unit of inheritance

Each gene codes for a different characteristic and makes up our DNA

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(6.2) Asexual reproduction

One parent is involved with asexual reproduction, therefore there is no variety.

Offspring from asexual reproduction are known as clones.

Body cells reproduce asexually to replace worn out tissue (growth and repair).

Bacteria and small plants commonly reproduce asexually.

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(6.2) Sexual reproduction

Sexual reproduction involves gametes.

Two parents are involved in sexual reproduction - this introduces variety because some characteristics are from the mother and some from the father.

Gametes in plant are called stamen (male) and ovules (female).

Gametes in animals are called sperm (male) and ova (female).

Variety is important because it allows some individuals to survive difficult conditions and reproduce.

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(6.3) Genetic and environmental differences

Both genetics and our environment can influence our characteristics.

Genetically identical plants (same nature) will look different if put in a different environment (different nurture).

Skin colour is decided by combined variance as it is inherited from the parents but will be darker in sunny environments.

Identical twins are so similar because they have the same genetic make-up as eachother.

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(6.4) Cloning plants

A clone is an individual produced asexually from its parent.

Gardeners can take cuttings of a plant to produce a clone:

  • Cut off a small part of a plant such as part of a stem or leaf
  • Plant this into soil

Using hormone rooting powder and providing moist conditions increase the chance of the cutting developing successfully.

Tissue culture can be used to produce thousands of clones of a plant very quickly:

  • Mix plant hormones to make a group of cells
  • Use a different mixture of hormones to grow a new plant from each cell

Cuttings are better for small scale gardening - cheaper and easier.

Tissue culture is better for large scale commercial gardening - produces more.

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(6.4) Cloning animals

Cloning can help farmers produce more high-quality calves because they can select high-quality parents and produce lots of genetically desirable offspring.

Cow eggs can be collected by:

  • Washing them out of her womb, already fertilised
  • Or they can be fertilised in a lab

Cloning cattle embryos:

  • Divide each embryo into cells
  • Each cell grows into an identical embryo in a lab
  • Transfer each into a host mother (the mothers are given hormones to prepare them for pregnancy)
  • Cloned calves are born
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(6.5) Adult cell cloning

Adult cell cloning is the production of a new animal clone from an adult cell.

  • Take nucleus from an adult cell from Animal 1
  • Remove nucleus from an egg cell from Animal 2
  • Place the nucleus from Animal 1 into the empty egg cell from Animal 2
  • Give the new cell a mild electric shock to stimulate fusion
  • Cell division begins
  • The embryo is implanted into a host mother's uterus
  • It develops and is born identical to Animal 1

Animals can be cloned by embryo cloning or adult cell cloning.

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(6.6) Genetic engineering

Genetic engineering is changing the genetic materal of an organism. We can use it to reproduce a human protein:

  • Cut out a gene from a cell using an enzyme
  • Insert gene into a bacterium
  • The gene continues producing the protein inside the bacterium
  • The protein can then be harvested and injected eg. insulin

Genes need to be transferred form the cells of one animal to another, because bacteria cannot produce all proteins.

Scientists used to get insulin from the pancreases of pigs and cattle before it could be produced by genetic engineering, but it wasn't suited to humans so anti-rejection tablets had to be taken with it.

GM crops can reduce starvation in developing countries by increasing growth rate and improving crop success.

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(6.6) Human enineering

Human engineering is the use of genetic modification to solve genetic diseases.

There are problems that can arise from genetic engineering:

  • Pests could become resistant
  • Ethical issues with 'designer babies'
  • Uncertainties about long term health implications
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(6.7) Making choices about technology

There are problems with cloning pets:

  • People need to learn how to grieve
  • There are already lots of unwanted pets
  • Cloning is expensive and difficult
  • The cloned pet won't even look the same as the original

People are worried about the safey of GM crops, but an example of where they have been beneficial is 'golden rice'

GM crops help reduce child blindness in the developing world - by modifying rice crops to produce beta-carotene, vitamin A deficiency (which causes blindness) can be reduced in countries where rice is a staple food.

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