topic b6- inheritance, variation and evolution

• DNA

  • code for amino acids for proteins
• DeoxyriboNucleic Acid 


  • the chemical a cell's nuclear genetic material is made from
• DNA

  • what's in your DNA determines what inherited disorders you have
  • DNA is a polymer made up of 2 strands coiled into a double helix
• chromosomes

  • long molecules of DNA that normally come in pairs
  • XY - male
  • XX - female
• gene

  small section of DNA found on a chromosome
• • each gene codes for a particular sequence of amino acids, which are put together to make a specific protein
  • only 20 amino acids are used, but they make thousands of different proteins
  • DNA determines what protein the cell produces
  • that determines what type of cell it is
  • 3 bases code for 1 amino acids
• genome 


  an organism's entire set of genetic material
• the complete human genome has been worked out

  • genes linked to diseases can be identified
  • this helps us understand inherited diseases, so we can develop effective treatments
  • tiny differences in people's genomes can be studied
  • this helps us trace the migration patterns of past human populations
• reproduction- asexual

  • parents- one parent
  • cell division- mitosis
  • produces- genetically identical offspring
  • advantages:
  • fast
  • only one parent needed
  • many identical offspring can be produced in favourable conditions
  • bacteria, plants and some animals
• reproduction- sexual

  • parents- two parents
  • cell division- meiosis and mitosis
  • produces- offspring containing a mixture of the parent's genes
  • advantages:
  • genetic variation
  • increased chance of survival
  • inherited characteristics
  • humans, animals + flowering plants
• meiosis

  • gametes are produced by meiosis, they have 1 copy of each chromosome
  • only happens in the reproductive organs
  • involves 2 cell divisions
• meiosis example

  
• meiosis

  1. the cell duplicates its genetic information
  2. the cell divides + each new cell has one copy of each chromosome
  3. both cells divide again to make 4 gametes
  4. each gamete only has a single set of chromosomes

  • all are genetically different
• X and Y chromosomes

  • 23 pairs of chromosomes in humans
  • males XY
  • females XX
• • to find the probability of getting a boy or a girl, you can draw a genetic diagram
  • they show all of the possible outcomes
• punnet square diagram

  female 50:50 chance of having either a girl or a boy

  X X

  m X XX XX

  a

  l Y XY XY

  e
• allele

  a version of a gene
• dominant allele

  an allele that is always expressed (only need 1)
• recessive allele

  an allele that is only expressed when 1 copies are present
• homozygous

  both of an organism's alleles for a trait are the same
• heterozygous

  an organism's alleles for a trait are different
• genotype

  an organism's combination of alleles
• phenotype

  the characteristics an organism has
• a punnet square for a genetic cross between a pea plant homozygous for round peas and a pea plant homozygous for wrinkly peas

  r = recessive allele for wrinkly peas

  R R all of the offspring have round peas

  r Rr Rr

  r Rr Rr
• inherited disorders

  disorders caused by a certain allele that are inherited from your parents
• cystic fibrosis-caused by a recessive allele

  • body produces thick mucus in the lungs and pancreas
  • for a child to have the disorder both parents must be a carrier of the allele or must have the disorder themselves
• polydactyly- caused by a dominant allele

  • born with extra fingers or toes
  • can be inherited if just one parent carries the allele
  • the parent that carries the allele will have the condition too because it is a dominant allele
• embryonic screening

  • in IVF it is possible to remove a cell from the embryo and analyse its genes
  • can be used to detect genetic disorders
• against embryonic screening

  1. implies that people with genetic problems are "undesirable" which increases prejudice
  2. people might want to screen their embryos so they can pick the most "desirable one"
  3. screening is expensive
• for embryonic screening

  1. it will help to stop people suffering
  2. treating disorders costs the government a lot of money
  3. there are laws to stop it going too far e.g. you cannot select the gender of your baby
• variation

  • differences in the characteristics of an organism
  • two types:
  • genetic
  • environmental
• different genes cause genetic variation

  • these genes are passed on in gametes (sex cells)
  • e.g. eye colour, blood group, inherited disorders
• characteristics are influenced by the environment

  • differences in conditions
  • e.g. leaves colours
• most characteristics have both

  • e.g. weight, height, skin colour, academic, athletic ability
• variation

  • organisms of the same species have differences
  • mutation are changes to the genome
• mutations can affect variation

  • can result in a new phenotype being seen in a species
• theory of evolution

  • all of today's species have evolved from simple life forms that first started to develop over three billion years ago
  • survival of the fittest
• charles darwin

  • came up with the theory of evolution by natural selection
  • species with more suitable characteristics will be more likely to survive and reproduce
  • published the origin of the species 1859
  • people disagreed:
  • lack of evidence
  • hadn't discovered genes
  • religious beliefs
• alfred russel wallace

  • discovered evolution with darwin
  • join wrote the book 1858
• extinction reasons

  1. the environment changes too quickly
  2. a new predator kills them all (e.g. humans)
  3. a new disease kills them all
  4. cannot compete with another species for food
  5. a catastrophic event kills them all (volcano)