Inheritance Variation and Evolution

• DNA (deoxyribonucleic acid)


  the chemical all genetic material of a cell is made up from
• where is DNA found

  found in a nucleus of animal and plant cell in long structures called chromosomes
• what is the structure of DNA

  a polymer made of two strands coiled together in a double helix structure
• genome

  the entire set of genetic material in an organism
• why is it important scientists have worked out the complete human

  allows to link diseases to specific gene

  helps develop treatment for disease

  allows finding ancestors
• gene

  a small section of DNA found on a chromosome
• what is the role of DNA

  codes for a particular sequence of amino acids put together to make a specific protein

  20 amino acids are used
• what does the DNA do with the protein

  DNA determines the protein a cell produces causes specialisation
• Protein synthesis

  1. DNA strands are polymers made up of lots of repeating units called nucleotides

  2. Each nucleotide consists of one sugar molecule, one phosphate molecule and one ‘base’

  3. The sugar and phosphate molecules from a ‘backbone’ to DNA strands, each molecule is alternate

  4. One of the bases A,T,C,G join to each sugar

  5. A goes with T and C goes with G in a complementary pairing

  6. The order of the bases determine the order of the amino acids in the protein

  7. Each amino acid is coded by a sequence of the three bases in the gene

  8. Parts of DNA are non-coding parts that switch genes on and off to control if the gene is expressed
• how are proteins made in ribosomes if DNA is in a he nucleus

  to make proteins ribosomes use the code from DNA, DNA is too big to travel from the nucleus. mRNA copies the code from the DNA and acts as a messenger between the DNA and the ribosome. The ribosomes use this to put the amino acids in the correct order
• three functions of proteins

  enzymes - biological catalysts

  hormones - carry messages

  structural proteins- physical strong
• sexual reproduction

  where genetic info from two organisms to produce offspring genetically different to either parent

  involves fusion of male and female gametes

  offspring inherit mixture from parents due to mixture of chromosomes

  → flowering plants have egg cells and pollen is sperm
• asexual reproduction

  there's only ONE parent,

  there's no fusion of gametes

  a mixing of chromosomes or genetic variation between parent and offspring - they're clones (genetically identical)

  → happens by mitosis with ordinary cells
• gametes

  only have one copy of each chromosome so that with gamete fusion the cell results in the correct number of chromosomes again
• meiosis

  is the process where gametes are made only happening in reproductive organs
• what happens after fertilisation

  after fertilisation occurs where two gametes have fused mitosis occurs and repeats many times to make a copy of the cell
• how do these become specialised

  differentiation then occurs changing the cells to specialised cells
• alleles

  traits (dominant or recessive)
• genotype 


  genetic code for a trait
• phenotype 


  the particular trait
• homozygous

  the same type be each parent (AA or aa)
• heterozygous

  different from each parent (Aa)
• describe the process of meiosis

  Before the cell stats to divide, the genetic material duplicates forming

  two identical chromosomes arms, and arrange is pairs.

  In the first division, the chromosome pairs line in the middle of the cell.

  The pairs are pulled apart, each cell has one copy of each chromosome -

  father's, mother's.

  In the second division, chromosomes line up again. Arms pulled apart

  You get four gamales, each with anly a single set of chromosomes. Each gamete is genetically different as chromosomes are shuffled + each get half