Biolody - B6

  • Created by: abbiedye
  • Created on: 21-06-18 20:57

What is DNA?

- The chemical that all of the genetic material in a cell is made from

- Contains coded information (characteristics)

- A polymer - made of two strands in a double helix

- Found in chromosomes

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What are genes?

- A small section of DNA found on a chromosome

- Each gene codes for a particular sequence of amino acids - specific protein

- Genes simply tell cells in what order to put the amino acids together

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What is a genome?

- The fancy term for the entire set of genetic material in an organism

- Important tool for science and medicine

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What is sexual reproduction?

- Mother and father produce gametes by meiosis

- In humans, each gamete contains 23 chromosomes (1 of each)

- The egg and the sperm cell fuse together to form a cell with the full number of chromosomes

- Variation of genes

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What is asexual reproduction?

- Only one parent  - the offspring are genetically identical

- happens by mitosis - an ordinary cell makes a new cell by dividing in two

- The new cell has exactly the same genetic information as the parent cell - it's called a clone

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What are gametes?

- Only have one copy of each chromosome

- When gamete fusion takes place, you get the right amount of chromosomes 

- Gametes are made in meiosis - which is two cell divisions

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What is meiosis?

- Produces four gametes , each with only a single set of chromosomes

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What chromosomes determine the two genders?

- Males have an X and a Y chromosome: XY. The chromosome causes male characteristics

- Females have two X chromosomes: **. The ** combination allows female characteristics to develop

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What do genetic diagrams show?

- the possible alleles of offspring from each parent

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What is cystic fibrosis?

- a genetic disorder of the cell membrane

- caused by a recessive allele

- thick mucus

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What is polydactyly

- genetic disorder

- caused by a dominant allele

- extra fingers or toes

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How can embryos be screened for genetic disorders?

- Before being implanted, cells can be removed to be analysed


  • stop suffering
  • there are laws stopping it from going too far 


  • people with disorders are 'undesirable'
  • expensive
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What are variations?

- slight differences in species

- genetic - hair colour, nose shape, height

- environmental - sun, light, moisture (plants)

- phenotypes - often both genes and environments

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What are mutations?

- a rare, random change in an organisms DNA that can be inherited

- this change can lead to variation

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What is the theory of evolution

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

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What was Charles Darwin's input to evolution?

- evolution by natural selection

- saw a wide variation in animal's characteristics

- the ones with the most suitable characteristics for the environment would be more likely to survive. 'survival of the fittest' 

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What are the reasons for extinction?

1. The environment changes too quickly

2. A new predator kills them all

3. A new disease kills them all

4. They can't compete with another (new) species for food

5. A catastrophic event happens that kills them all

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What is selective breeding?

- when humans artificially select the plants or animals that are going to breed to get the best characteristics


  • Animals that produce more meat or milk
  • Crops with disease resistance
  • Dogs with a good, gentle temperament
  • Plants with big or unusual flowers
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What is the basic process of selective breeding?

1. Select the desired characteristics from the existing stock

2. Breed them with each other

3. Select the best of the offspring, and breed them together

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What is the main drawback in selective breeding?

-The main drawback is a reduction in the gene pool

Selective breeding  ->  reduction in the number of different alleles (forms of a gene)  ->  less chance of any resistant alleles being present in the population

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What is genetic engineering?

- To transfer a gene responsible for a desirable characteristic from one organism's genome into another organism, so that it also has the desired characteristic

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What is the process of genetic engineering

1. A useful gene is isolated from one organism's genome using enzymes and is inserted into a vector

2. The vector is usually a virus or a bacterial plasmid

3. When the vector is introduced to the target organism, the useful gene is inserted into its cell(s)

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Why is genetic engineering a controversial topic?

- it has the potential for solving many problems

- there are worries about the long-term effects of genetic engineering -  changing an organism's genes might accidentally create unplanned problems

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What are the pros and cons of GM crops?


  • characteristics chosen for GM crops can increase the yield
  • can contain missing nutrients
  • are being grown with no problems


  • affect the number of wildflowers - reduce biodiversity
  • might not be safe
  • transplanted genes may get out into the natural environment
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How are fossils formed?

1. Gradual replacement by minerals - teeth, shells, bones don't decay

2. From casts and impressions - an organism that is buried in a soft material (clay)

3. Preservation - no decay - in amber and tar pits (no oxygen/moisture), glaciers (too cold) and peat bogs (too acidic)

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How can bacteria evolve and become antibiotic-resi

- They sometimes develop random mutations in their DNA

- MSRA - 'superbug'

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How common is antibiotic resistance?

- Overuse and inappropriate use of antibiotics - non-serious conditions

- More often antibiotics are used, the bigger problem of antibiotic resistance

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What is classification?

- Organising living organisms into groups 

- Carl Linnaeus - 1700s

- Classification system -

  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
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What are classification systems?

- Carl Woese - 1990

Archea - primitive bacteria - extreme places - hot springs and salt lakes

Bacteria - true bacteria - E.coli and Staphylococcus - similar to archaea

Eukaryota - fungi, plants, animals, and protists

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How are organisms named?

- Binomial system - two-part Latin name

- First part - genus = ancestry

- Second part - species

Homo = genus, sapiens = species

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What are evolutionary trees?

- They show how different species are related - common ancestors

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