AOS 1

• complete dominance


  dominant allele completely masks the recessive one
• incomplete dominance: the dominant allele does not completely maks the recessive allele, creating an intermediate offspring
• codominance


  both alleles are equally and independently expressed
• autosomal dominant: -males and females are evenly affected

  -affected individuals have at least one affected parent
• autosomal recessive: -males and females are evenly affected

  -unaffected parents can have affected children
• x-linked dominant: -affected males pass condition onto all daughters but no sons

  -> mother or affected male will be also affected

  -affected individuals have at least one affected parents

  -more common in females
• x-linked recessive: -affected females always have an affected father + son

  -daughters can be carriers

  -more common in males
• Chromosomes


  • are thread - like structures located inside the nucleus of animal & plant cells
  • each made up of protein and DNA
• Genome


  refers to all the genetic material in one haploid set of chromosomes
• Haploid Cells (1n)


  Contains 1 set of chromosomes

  eg. sex cells, sperm&egg
• Diploid cell (2n)


  contains 2 sets of chromosome, one from mum, one from dad

  23 -> 46

  eg. body cells
• Genes


  sections of DNA that codes for proteins

  • position of a gene in a chromosome is called a locus and is the same for everyone
• Alleles


  variations of a gene

  eg. Gene = Hair colour, allele = black or brown
• DNA


  is a double - stranded helix made up of amino acids held together by hydrogen bonds
• Nucleotides 


  • building blocks of DNA
  • contain a phosphate group, pentose sugar and a nitrogenous base -> adenine + thymine (2), cytosine + guanine (3)

  
• Fertilisation


  when the nucleus of a sperm fuses with an egg nucleus, the diploid number of chromosomes is restored
• Germ Cell


  any biological cell that gives rise to the gametes of an organism that reproduces sexually
• Meiosis


  is the process that produces gametes that have a haploid number of chromosomes
• Meiosis 1 (prophase)

  • chromosomes condense, becoming visible
  • chromosomes align with their homologus pairs and cross over (synapse)
  • nuclear membrane disappears
• Meiosis 1 (metaphase 1)

  • chromosomes line up across the equator of the cell
  • are not in a single file, they are pairs down the middle
  • independent assortment
• Meiosis 1 (anaphase 1)


  are pulled by spindles to opposite poles of the cell
• Meiosis 1 (Telophase 1 & cytokinesis)

  • nuclear membrane forms around each group of separated single chromosomes
  • chromosomes decondense and cells divide into 2 daughter cells
• monoploidy


  different to haploid as all cells have 1n, not just the sex cells
• polyploidy


  triploid, tetraploid
• Autosomes (homologous)


  • matched pairs of chromosomes (1-22)
  • pairs have same genes, but different alleles
• SEX chromosomes


  the X & Y chromosomes
• Homologous pairs


  a pair of chromosomes that have the same genes. 1 is inherited from mum, the other from dad
• Aneuploid 


  having an abnormal number of chromosomes in a haploid set
• Non - Disjunction 


  refers to the chromosomes failing to seperate correctly, resulting in gametes with one extra, or one missing, chromosome
• Genotype


  genetic makeup of an organism

  makes up the traits that an organism inherits from it's parents
• Heterozygous 


  Ww ( 1 dom, 1 recessive allele)
• Homozygous dom


  WW ( 2 dom alleles)
• Homozygous recessive


  ww ( 2 recessive alleles)
• Phenotype 


  the visible/ measurable expression of the genetic make - up of an organism (i.e. the traits or characteristics that result from the genotype)
• Sex - linked recessive

  more males are affected than females

  • if mum is carrier, sons are 50:50 affected, NOT daughters
  • if dad is affected, daughters are carriers
  • NO dad-son transmission
  • NO male carriers
• Sex - linked dominant

  Female carriers -> are affected, and have a 50% chance of affecting her children regardless of gender

  • If dad is affected -> ALL daughters are affected
  • NO dad - son transmission
  • NO male carriers