17. Inheritance

• Inheritance - the transmission of genetic information from generation to generation
• Chromosome - thread like structure made of nucleic acids and proteins that carry genetic information in the form of genes
• Gene - small section of DNA that codes for a specific combination of amino acids which creates a specific protein

  • the bases sequences is the genetic code for putting together amino acids in the correct order to make a specific protein
  • DNA controls cell function - controlling the production of proteins, antibodies, receptors & neurotransmitter
  • not all cells are expressed since only specific genes code for specific protein
• Allele - alternative form of genes
• XX chromosome - female

  XY chromosome - male
• DNA v.s RNA

  DNA:

  • long molecule (polynucleotide) - long chain of many nucleotide join together
  • nucleotide consists of phosphate (deoxyribose) sugar, and (nitrogenous) base
  • double stranded
  • T&A, G&C

  RNA:

  • long molecule (polynucleotide) - long chain of many nucleotide join together
  • consists of phosphate, a (ribose) sugar and nitrogenous base
  • single stranded (half size of DNA)
  • A&U, G&C
• mRNA (messenger RNA) - single stranded nucleotide that carries the message from the nucleus to the ribosome to be translated
• tRNA (transfer RNA) - single stranded nucleotide that brings the specific amino acid down to the ribosome
• Protein synthesis (TRANSCRIPTION):

  1. DNA unzips along the gene which codes for the desired protein
  2. leaves the bases on DNA strands exposed
  3. free RNA nucleotides which are found in nucleus move in and line up opposite the exposed base by complementary base pairing
  4. RNA nucleotides join together to form a strand of mRNA
  5. mRNA leaves the nucleus and travels to ribosome in cytoplasm
• Codon - a sequence of 3 bases on the mRNA molecule
• Protein synthesis (TRANSLATION):

  1. mRNA arrives at ribosome and move through one codon at a time
  2. the specific tRNA with the anti-codon that is complementary to the codon lines up
  3. depending on the anti-codon, tRNA travels through the cytoplasm and picks up the specific amino acid and brings it down to the ribosome
  4. the next tRNA goes through the same process and bring up its own amino acid to the ribosome
  5. process continues until the ribosome reads a 'stop codon' on mRNA
  6. each amino acids joins to the adjacent ones to form the protein
• Haploid nucleus - a nucleus containing a single set of unpaired chromosome (23 chromosome)
• Diploid nucleus - a nucleus containing two sets of chromosomes (46 chromosomes)

  • in diploid cell - a pair of each type of chromosome (in human = 23 pairs)
• Mitosis - nuclear division giving rise to genetically identical cells

  • helps growth and repair of cells, repair damage tissues, replacement of cells & asexual reproduction

  Stages:

  • every single chromosome has replicate itself in parent cell
  • chromosome move to the equator of the cell and the spindle fibres (long chain of protein) attach
  • one chromosome from each pair of replicated chromosomes is pulled to opposite poles
  • each pole now contains a FULL set of identical chromosome

  
• Stem cells - unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

  • found in embryo, bone marrow, liver, brain muscle and blood
• Meiosis - nuclear division where 4 genetically different nuclei are form from 1 parent cell nucleus

  • involve in the production of gametes
  • create variation - different combination of genetic material in daughter cell

  Stages:

  • parent cell - DNA replication has occurred
  • chromosomes move to the equator of cell and the spindle fibres attach
  • one chromosome from each pair of chromosomes in pulled to opposite poles
  • each pole now contains a HALF set of chromosomes (haploid number in daughter cells)

  
• Genotype - set of alleles an organism has for a particular gene
• Phenotype - the way that a characteristic is expressed on an individual
• Homozygous - a genotype containing the same alleles

  • two identical homozygous individuals breeding = pure-breeding
• Heterozygous - a genotype containing different alleles

  • would not be pure-breed
• Dominant - allele that is expressed if its is presented in a genotype
• Recessive - an allele that is only expressed as an allele when there are no dominant allele in a genotype
• Pedigree diagram:

  • inheritance of a characteristic

  
• Punett square:

  • calculating ratio/ percentage of a characteristic in the offspring

  
• Co-dominance - when both alleles in heterozygous organism contribute to the phenotype (e.g. bloodtype)

  • IA, IB and IO
  • IA and IB are co-dominant giving blood group AB
  • both IA and IB are dominant to IO

  Picture ratio:

  • A:B, 1:1

  
• Sex-linked characteristic - a characteristic in which the gene responsible is located on a sex chromosome and this make it more common in one sex that the other

  • e.g. red-green color blindness