inheritance, variation and evolution

• chromosomes are really long molecules of DNA
• DNA determines what inherited characteristics you have
• DNA is coiled together in the shape of a double helix
• a gene is a small section of DNA that codes for a specific protein.
• genes also determine what type of cell it is, e.g. red blood cell, skin cell
• every organism has a unique genome, which is the complete set of genes in an organism
• genome- entire set of genetic material in an organism
• human genome allows

  • us to identify genes in the genome that are linked to different types of disease
  • knowing which genes are linked to inherited diseases could help develop effective treatments
  • could be used to help to trace migration patterns
• DNA is made up of nucleotides
• each nucleotide consists of a sugar phosphate group and one 'base'
• the four bases are A , T , C , G
• complementary base pairing

  • A and T
  • C and G
• the order of bases in a gene decides the order of amino acids in a protein
• each amino acid is coded by three bases in the gene
• there are parts of DNA that don't code for proteins. some of these non- coding parts switch genes on and off, so they control whether or not a gene is expressed
• mRNA carries the code to the ribosomes
• to make proteins, ribosomes use the code in the DNA
• the mRNA acts as a messenger between the DNA and the ribosomes - it carries the code between them both
• protein functions

  1. enzymes - act as a biological catalyst to speed up chemical reactions in the body
  2. hormones - used to carry messages around the body
  3. structural proteins - are physically strong
• mutations are changes to the genetic code
• the chance of mutation is increased by exposure to certain substances or some types of radiation
• mutations change the sequence of the DNA bases in a gene, which can lead to a change in the amino acid sequence of a protein
• if there's a mutation in the non - coding DNA, it can alter how genes are expressed
• insertions are where a new base is inserted into the DNA base sequence where it should'nt be
• insertions can change more than one amino acid as they have a knock-on effect on bases further on in a sequence
• deletions are when a random base is deleted from the DNA base sequence
• substitutions mutations are when a random base in the DNA base sequence is changed to a different base
• sexual reproduction produces genetically different offspring, so there is variation
• in sexual reproduction, the mother and father produce gametes by meiosis
• in humans, each gamete contains 23 chromosomes
• the mixture of genetic information produces variation in the offspring
• flowering plants can also reproduce sexually as well. they also have egg cells
• asexual reproduction produces genetically identical cells
• asexual reproduction happens by mitosis
• in asexual reproduction, there is only one parent. there's no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring - they are clones
• bacteria , some plants and some animals reproduce asexually
• gametes only have one copy of each chromosome, so they are haploid
• meiosis produces cells with half the normal number of chromosomes
• in meiosis, you get 4 gametes with only a single set of chromosomes in it. each gamete is genetically different
• some organisms can reproduce by both methods

  • malaria spread by mosquitoes
  • many species of fungus. they release spores which can become new fungi when they land in a suitable place
  • loads of species of plants produce seeds sexually, but they can also reproduce asexually