Genetics

• describe the structure of DNA

  • two strands coiled to form a double helix
  • each strand is made up of lots of monomers called a nucleotide
  • DNA is a polymer
• what is a nucleotide

  a monomer made up of phosphate which is bonded to a sugar and one of the four complementary bases (A, T, C, G)
• which complementary bases pair with each other and what are they joined by

  • A - T
  • C - G
  • they are joined by weak hydrogen bonds
• what is a genetic code

  a sequence of bases
• what is a gene

  a particular sequence of bases that codes for a protein
• what is a genome

  the entire DNA of an organism
• how do you extract DNA from fruit

  1. mix together 50ml of cold water, teaspoon of salt, and 10ml of washing up liquid
  2. mash up the fruit
  3. add fruit to mixture
  4. place in a water bath with temperature of 50 to incubate for 10 minutes
  5. add ice cold ethanol-a white cloudy substance will form on the top(DNA)
• when extracting DNA why do you mash the fruit

  to break the cell membrane
• when extracting DNA why add washing up liquid

  to separate the DNA
• when extracting DNA why add ice cold ethanol

  DNA is not soluble in ethanol so it will precipitate
• how is protein formed from DNA bases

  • each group of three bases codes for an amino acid (e.g ATC)
  • the amino acids are joined together and fold to make a protein
• what determines what protein it is

  • the order of amino acids
  • this is because proteins are often enzymes which need to have a specific shape
• what are the two main stages in protein synthesis

  • transcription
  • translation
• what are the stages of transcription(protein synthesis)

  1. RNA polymerase binds to the non-coding DNA located in front of the gene
  2. two DNA strands pull apart and RNA polymerase allows mRNA nucleotides to match their complementary base on the strand
• what are the stages of translation(protein synthesis)

  1. the mRNA moves out of the nucleus to the ribosomes
  2. the bases on mRNA are read in triplets to code for an amino acid
  3. the corresponding amino acids are brought to the ribosomes by tRNA (transport RNA)
  4. these amino acids connect together to form a polypeptide and when the chain is complete it forms the final protein
• what are genetic variants

  small changes in the order of bases
• what is the effect of genetic variants in the non-coding DNA

  • genetic variants can be produced if a mutation occurs in the non-coding DNA of a gene
  • this can affect the phenotype by influencing the binding of RNA polymerase
  • this means its more difficult to bind so less mRNA will be transcribed and less protein produced
• what is the effect of genetic variants in the coding DNA

  • the genetic variant will alter the sequence of bases
  • therefore it will change the sequence of amino acids
  • this will alter the final structure of the protein produced
• what is a phenotype

  the visible effects of the genes (characteristics you get from your genotype)
• what are the advantages of sexual reproduction:

  • it produces variation in the offspring
  • the species can adapt to new environments due to variation, which gives them a survival advantage
  • a disease is less likely to affect all the individuals in a population
• what are the disadvantages of sexual reproduction:

  • time and energy are needed to find a mate
  • it is not possible for an isolated individual
• what are the advantages of asexual reproduction include:

  • the population can increase rapidly when the conditions are favourable
  • only one parent is needed
  • it is more time and energy efficient as you don't need a mate
  • it is faster than sexual reproduction.
• what are the disadvantages of asexual reproduction include:

  • it does not lead to variation in a population
  • the species may only be suited to one habitat
  • disease may affect all the individuals in a population
• what does mitosis produce

  Mitosis produces identical diploid body cells for growth and repair
• what does meiosis produce in animals

  egg and sperm cells
• what does meiosis produce in plants

  pollen and egg cells
• what does meiosis produce

  • production of four daughter cells, each with half the number of chromosomes
  • this results in the formation of genetically different haploid gametes
  • These fuse to form a diploid fertilised egg cell during fertilisation.
• what did Gregor Mendel do?

  carried out breading experiments on pea plants
• describe Gregor Mendel's experiment

  1. he used both smooth, wrinkled, green and yellow peas to observe the offspring to see which characteristics they had inherited
  2. he came to the conclusion that offspring have the same characteristics that they parents have because they inherit hereditary units from each
  3. one unit is received from each parent
  4. units can be dominant or recessive
• what is a gamete

  an organism's reproductive cell (egg or sperm)
• what are chromosomes

  a structure found in the nucleus which is made up of a long strand of DNA
• what is a gene

  a short section of DNA that codes for a protein and contribute to a characteristic
• what are alleles

  different forms of the gene, there are 2 alleles for each gene
• what is a dominant allele

  an allele that only needs one of it for it to be expressed (Aa- A is dominant allele)
• what is a recessive allele

  an allele that needs two copies of it for it to be expressed
• what is homozygous

  both inherited alleles are the same (aa)
• what is heterozygous

  when one allele is dominant and the other is recessive
• what is a genotype

  a combination of alleles an individual has
• what is a phenotype

  the physical characteristics an individual has
• what is a zygote

  when a diploid cell formed from the fusion of two haploid gametes