Inheritance variation & evolution

• DNA

  Deoxyribonucleic acid, the chemical that all of our genetic material is made of
• DNA

  • It's a polymer made up of lots of similar units stuck together
  • It has two strands which are stuck together to form a double helix
• If you unraveled all the DNA in a single cell, the strand would be over two meters long
• Chromosome

  A really tight coil of DNA, each cell has 46 chromosomes
• There are 23 different types of chromosomes, with two of each type (one from each parent)
• Sex chromosomes

  The 23rd pair, consisting of an X chromosome and a Y chromosome
• Chromosomes only look like an X shape just before cell division
• Gene

  A small section of DNA that codes for a particular type of protein
• There are 20 different types of amino acids that can be combined in many different sequences to form thousands of different proteins
• Genome

  The entire set of genetic material in an organism
• Scientists have worked out the complete human genome, which allows them to identify genes linked to diseases and develop better treatments
• Genomes can be used to trace the migrations of human ancestors
• Allele

  Different versions of the same gene
• Homozygous

  Having two of the same alleles for a particular gene
• Heterozygous

  Having two different alleles for a particular gene
• Dominant allele

  The allele that gets expressed when present, regardless of the other allele
• Recessive allele

  The allele that only gets expressed when two copies are present (homozygous recessive)
• Genotype

  The entire collection of alleles an organism has
• Phenotype

  The characteristics an organism displays, determined by its genotype
• DNA

  Two strands wrapped around each other in a double helix
• Structure of DNA

  1. Nucleotides

  2. Complementary base pairing

  3. Gene coding for a protein
• Nucleotide

  Monomer unit of DNA, made up of a phosphate, sugar, and base
• Bases in DNA

  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• DNA

  • Polymer made up of many nucleotides
  • Sugar phosphate backbone forms protective outer casing
  • Bases hold the two strands together through complementary base pairing
• Complementary bases

  A pairs with T, C pairs with G
• Determining complementary DNA strand

  Look at sequence of one strand and determine complementary bases for other strand
• Genetic code

  Sequence of DNA bases
• Gene

  Particular sequence of bases that codes for a protein
• Protein synthesis from DNA

  1. DNA sequence read as triplet codes

  2. Amino acids coded for by triplets combined in order

  3. Chain of amino acids folds to form protein
• Proteins

  • Each type has a unique shape that allows it to carry out a particular function
  • Main uses are in enzymes, hormones, and structural proteins
• Protein synthesis


  The process of making proteins
• Protein synthesis

  1. Transcription

  2. Translation
• Transcription

  The process of taking a single gene of DNA and copying it into a structure called mRNA
• Translation

  The process of taking the mRNA strand and using it to produce a protein
• Inside almost every cell is a nucleus that contains all the genetic material of that cell in the form of DNA
• Gene

  Small sections of the DNA that have a specific sequence of bases and are able to code for a specific sequence of amino acids
• The specific sequence of bases has to be read by structures called ribosomes which are outside of the nucleus
• mRNA

  A copy of a single gene that is small enough to leave the nucleus and make its way to the ribosome
• mRNA

  • It is much shorter than DNA because it's only a single gene long
  • It is a single strand rather than a double strand like DNA
  • It contains the base uracil instead of thymine
• Transcription

  1. RNA polymerase binds to the DNA

  2. The two strands of DNA separate

  3. RNA polymerase reads the DNA bases and uses them to make an mRNA strand

  4. The mRNA strand is then free to leave the nucleus