DNA and inheritance

• DNA is a large complex polymer. It's made up of two stands forming a double helix. Every DNA is unique.
• What are chromosomes found?

  Nucleus
• What is a gene?

  Is a section of coding DNA
• A gene codes for a particular sequence of amino acids.
• What is a allele?

  Different variations of the same gene?
• What is a genotype?

  Collection of alleles that determine the characteristics and can be expressed as a phenotype
• What is a phenotype?

  Visible characteristics of an organisms e.g. hair is brown
• What is meant by the term dominant allele?

  An allele that is always expressed in the phenotype if present
• What is meant by the term recessive allele?

  An allele that is only shown in the absence of a dominant allele
• What is homozygous?

  Alleles that are both identical. E.g. AA aa
• What is meant by heterozygous?

  Alleles that are both different. E.g. Aa
• What is a gene in the unit of?

  Heredity
• Chromosomes are long threads of DNA
• Who worked out the structure of the DNA?

  James Watson and Francis Crick
• The 'backbone' of each DNA strand is made from alternating sugar and phosphate molecules with paired chemicals between each strand called bases.
• 4 different bases in DNA:

  • Thymine
  • Adenine
  • Guanine
  • Cytosine

  T-A G-C
• What does DNA contain?

  It contains genetic code which is made up of sets of three bases called a triplet coding
• The sequence of every amino acid in a protein is determined by the triplet coding, which is a code of three bases.
• What does a test cross allow you to find?

  Allows you to find if an organism showing a dominant characteristic is homozygous or heterozygous.
• What is the locus?

  Position of the gene
• Where can you find DNA?

  • Blood
  • Sweat
  • Semen
  • Hair follicles
  • Skin
  • Silvia
• Humans have 23 pairs of chromosomes in the nucleus. Of these, 22 pairs are known as autosomes, and control characteristics but one pair carries genes that determine sex - whether offspring is female or male
• Male chromosomes are XY
• Female chromosomes are XX
• What is this diagram know as?

  Karyotypes

  
• In the human genome there is a small amount of DNA that is unique to individuals
• Genotypic ratio?


  R r

  R RR Rr

  r Rr rr

  RR:Rr:rr

  1 : 2 : 1
• Phenotypic ratio?


  R r

  R RR Rr

  r Rr rr

  Red:Yellow

  3 : 1
• How to produce a DNA fingerprint:

  1. DNA is cut into small pieces using a restriction enzyme
  2. These pieces are then 'ran' on an electrophoresis gel that has an electrical charge sent through it. This is called gel electrophoresis
  3. DNA is pulled through the gel
  4. The small pieces travel the furthest
  5. Therefore the gel separates the cut pieces of the DNA
• What are the uses to DNA profiling?

  • Provide evidence to identify suspects
  • Paternity cases
  • To compare different species for classification
  • Cystic fibrosis in babies
• Disadvantages to genetic profiling?

  • Storage on DNA profiles can be seen as an invasion of privacy
  • Theft of DNA profiles from a database can be seen as a real threat
  • Can plant DNA at a crime scene
• Natural selection question

  • Mutation occurs - Giraffe born with longer neck than other giraffes
  • Mutation confers an advantage in its environment - longer neck allows giraffe to reach higher leaves
  • This advantage allows organism to survive long enough to breed - Giraffe reaches higher leaves - survives to breed
  • Passes on advantageous gene to offspring - passes on longer neck gene to offspring
• DNA consists of two strands coiled into a double helix.