B6 - Inheritance, Variation and evolution

• chromosomes are really long molecules DNA
• DNA : it is the chemical that all of the genetic material in a cell is made up from. it contains coded information basically all the instructions to put an organism together and make it work. so it is what's in your DNA that determines what is inherited characteristics you have. DNA is found in the nuclease of animal and plant cells in really long structures called chromosomes. DNA is a polymer it is made up of two strands coiled together in the shape of a double helix
• a gene codes for a specific protein
• A gene is a small section of DNA found on a chromosome. each gene codes for a particular sequence of amino acids which are put together to make a specific protein. only 20 amino acids are used but they make up thousands of different proteins. genes simply tells cell in what order to put amino acids together. DNA also determines what proteins the cell produces e.g. haemoglobin. that in turn determines what type of cell it is e.g. red blood cells
• every organism has a genome
• genome is just the fancy term for the entire set of genetic material in an organism.
• sexual reproduction is where genetic information from two organism is combined to produce offspring which are genetically different to either parent. the mother and father produce gametes by meiosis. in humans each gamete contains 23 chromosomes. half come from mum and the other from dad. this is why the offspring inherits from both parents. it received a mixture of chromosomes from its mum and its dad. the mixture of genetic information produces variation in the offspring
• asexual reproduction produces genetically identical cells
• in asexual reproduction there is only one parent so offspring are genetically identical to that parent. it 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 is a clone e.g. bacteria and some plants
• gametes are produced by meiosis
• meiosis produces cells with half the normal number of chromosomes
• meiosis

  A) duplicates

  B) genetic

  C) information

  D) pairs

  E) first division

  F) pulled apart

  G) fathers

  H) mothers

  I) second division

  J) pulled apart

  K) four

  L) single set

  M) genetically different

  
• the cell produced by gamete fusion replicates itself
• after two gametes have fused during fertilisation the resulting new cell divides by mitosis to make a copy of itself. mitosis repeats many times to produce lots of new cells in an embryo. as the embryo develops these cells then start to differentiate into the different types of specialised cell that make up a whole organism
• males : XY
• female : XX
• the chance of having a boy or a girl is 50 %
• what gene you inherited controls what characteristics you develop. different genes control different characteristics. some characteristics are controlled by a single gene. however most characteristics are controlled by several genes interacting. all genes exist in different versions called alleles. you have two alleles of every gene in your body one on each chromosome in a pair.
• if two alleles are different they are heterozygous
• if two alleles are the same it is homozygous
• the characteristic that is shown in a capital letter is a dominant allele
• the characteristic that is not shown of in a lower case is recessive
• the genotype is the combination of alleles you have. your alleles work at a molecular level to determine what characteristics you have - phenotype
• cystic fibrosis is caused by a recessive allele
• cystic fibrosis is a genetic disorder of the cell membrane. it results in the body producing a lot of thick sticky mucus in the air passage and pancreas. for someone to have the disorder both parents must be either carriers or have it themselves
• polydactyly is caused by a dominant allele
• polydactyly is a genetic disorder where the bay is born with an extra figure or toe and is caused by a dominant allele so can be inherited if just one person carries the allele
• during IVF embryos are fertilised in a laboratory and then implanted into the mothers womb. before being implanted it is possible to remove a cell from each embryo and analyse its gene. many genetic disorders can be detected in this way such as cystic fibrosis. it is also possible to get DNA from an embryo in the womb and test that for disorders
• against embryo screening : it implies people with genetic problems are undesirable this could increase prejudice and is expensive
• for embryo screening : stop people from suffering and prevent birth defects
• mutation is a rare random change in an organism DNA that can be inherited
• mutations are changes to the genome
• variation can be genetic this means it is caused by difference in Genotype. an organisms genotype affects its phenotype the characteristics that it displays
• theory of evolution : all of todays species have evolved from simple life forms that first started to develop over three billion years ago
• Charles Darwin concluded that the organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive 'survival of the fittest' the successful organism that survives are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring. the organism that are less well adapted would be less likely to survive and reproduce so they are less likely to pass on their genes to the next generation
• The discovery of genetics


  Supported Darwin's idea of how organisms born with beneficial characteristics can pass them on
• The discovery of genetics

  Showed that it is genetic variants that give rise to phenotypes suited to the environment
• Looking at fossils of different ages allows you to see how changes in organisms develop slowly over time
• The relatively recent discovery of how bacteria are able to evolve to become resistant to antibiotics further supports evolution by natural selection
• The theory of evolution by natural selection is widely accepted