Inheritance, Variation, Evolution

• DNA stands for deoxyribonucleic acid


  it is the chemical that all of the genetic material is made up of
• DNA contains coded information 


  what is in the DNA determines the characteristics
• DNA is found in the nucleus in long structures called chromosomes


  Chromosomes normally come in pairs
• DNA is a polymer


  it is made up of two strands coiled together in the shape of a double helix
• 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
• 20 amino acids are used but they make up thousands of different proteins


  genes tell cells in what order to put the amino acids together

  determines what proteins the cell produces

  determines what type of cell it is
• genome is the entire set of genetic material in an organism


  scientists have worked out the entire human genome

  Human genome project 1990- team of scientists from all over the world worked together in tandem to map the human genome
• The human genome project allowed scientists to

  identify genes that are linked to different types of disease

  knowing which genes are linked to which diseases helps develop effective treatments

  trace migration to see where and when new populations split off
• DNA strands are polymers made up of nucleotides

  each nucleotide consists of a sugar, a phosphate, a base

  each base links to a base on the other strand of the helix (ATCG)

  this is complementary base pairing
• the order of bases in a gene decides


  the order of amino acids in a protein
• each amino acid is coded for by a sequence of three bases in a gene


  the amino acids are joined together to make various proteins, depending on the order of the gene's bases

  there are parts of the DNA that don't code for proteins, some non-coding DNA switches on and off so control whether or not a gene is expressed
• proteins are made in the cell cytoplasm ribosomes


  to make proteins, ribosomes use the code in the DNA, DNA is found in the nucleus and can't move out because it is too big

  the code is transferred between the nucleus and ribosome using mRNA which acts as a messenger between the DNA and ribosome

  the correct amino acids are brought to the ribosomes in the correct order by carrier molecules
• when a chain of amino acids has been assembled it folds into a unique shape


  this allows the protein to perform the task it is designed to do

  enzymes-biological catalysts

  hormones-carry messages around the body

  structural proteins-physically strong
• mutations are changes to the genetic code


  mutations can occur spontaneously

  the chance of mutations can be increased by exposure to certain substances or types of radiation
• mutations change the sequence of the DNA bases in a gene which produces a different genetic variant


  as a sequence of DNA bases code for the sequence of amino acids that make up a protein, mutations to a gene can lead to changes in the protein that it codes for
• most mutations have little to no effect

  some will change it to such a small extent that its function or appearance in unchanged

  mutations can severely affect a protein, can change its shape which can change its function
• if the shape of an enzymes active site is changed, it may not be able to bind to a substrate


  structural proteins could lose their strength
• if there is a mutation in non-coding DNA


  it can alter how genes are expressed
• there are different ways mutations can change the DNA base sequence


  insertions

  deletions

  substitutions
• insertions


  insertions are when a new base is inserted into a DNA base sequence

  an insertion changes the way the groups of three are read which can change the amino acid they code for

  can change more than one amino acid as they have a knock on effect
• deletions


  deletions are when a random base is deleted from a sequence

  they change the way that the base sequence is read and have knock on effects
• substitutions


  substitution mutations are when a random base in the DNA sequence is changed to a different base
• sexual reproduction produces genetically different cells


  sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically different to either parent

  the mother and father produce gametes via meiosis

  each gamete contains 23 chromosomes

  the egg and sperm fuse together to from a cell with 46 chromosomes
• sexual reproduction


  involves the fusion of female and male gametes

  there are two parents so the offspring contains a mixture of their parent's genes
• the mixture of genetic information creates variation 


  flowering plants can reproduce this way
• asexual reproduction produces genetically identical cells


  there is only one parent so offspring are genetically identical

  happens by mitosis

  new cell has exactly the same genetic information- it is a clone

  bacteria/some plant/animals reproduce asexually
• asexual reproduction


  only one parent

  no fusion of gametes no mixing of chromosomes and no genetic variation

  the offspring are genetically identical to their parent
• gametes are produces by meiosis


  gametes have only one copy of chromosomes so when gamete fusion takes place, there is the right number of chromosomes

  meiosis involves two cell divisions, in humans this only happens in reproductive organs
• meiosis


  before the cell divides, it duplicates genetic information + chromosomes arrange themselves into pairs- they line up in the centre of the cell. they are pulled apart so each cell has one copy of each chromosome some of the fathers and mothers go into each new cell

  in the second division, the chromosomes line up again and get split apart Produces four gametes with a single set of chromosomes, each gamete is genetically different from the others as the chromosomes get all shuffled up during meiosis
• after two gametes have fused during fertilisation, the 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 an embryo develops, the cells start to differentiate into the different types of specialised cell that make up a whole organism
• sexual reproduction VS asexual reproduction

  mixture of chromosomes- variation which increases the likelihood of an organism surviving a change in the environment

  individuals with characteristics that make them better adapted to the environment have better chances of survival and more likely to breed successfully and pass on characteristics- natural selection

  selective breeding speeds up natural selection
• asexual reproduction VS sexual reproduction


  one parent

  less energy

  faster

  produced in favourable conditions
• some organisms can reproduce by both methods

  malarial parasites

  fungi

  plants
• malarial parasites


  malaria is cause by a parasite that's spread by mosquitoes

  when a mosquito carrying the parasite bites a human, the parasite can be transferred to the human

  the parasite reproduces sexually when its in the mosquito and asexually in the human
• fungi


  release spores which can become new fungi when they land in a suitable place

  asexually-produced spores are identical to the parent

  sexually-produces spores introduce variation and are in response to an unfavourable change in the environment
• plants


  asexual reproduction can take place in many different ways- strawberry plants produce runners that grow horizontally on the surface of the soil away from a plant and at various points a new strawberry plant forms

  bulbs- new bulbs can form and divide off- each can form an identical plant
• there are 23 pairs of chromosomes


  22 matched pairs control characteristics

  the 23rd pair are XX or XY

  these two chromosomes decide your sex
• females have XX chromosomes 


  males have XY chromosomes
• when making sperm, the X and Y chromosomes are drawn apart

  this gives a 50% chance of the sperm cell getting either chromosome
• what genes you inherit control what characteristic you develop

  different genes control different characteristics, some are controlled by a single gene

  most are controlled by several genes interacting

  they exist in different version called alleles