Patterns of inheritance

• Co-dominance


  both alleles in the heterozygous individual are dominant and are both expressed in the phenotype (red and white flower)
• Incomplete dominance


  neither allele is dominant, therefore they are both expressed by mixed ( pink flower from white and red alleles)
• Pure-breeding


  homozygous genotype
• Hybrid 


  heterozygous genotype
• Genotype


  the combination of parent alleles
• Phenotype


  the physical expression
• Proportional heritability 


  the proportion of phenotypic variation that is influenced by the genes rather than environmental variation
• How does epigenetics work?

  DNA methylation ~ methyl groups (molecules) attach to certain nucleotides within a DNA sequence which and alter the levels of gene expression

  histone modification ~ histone methyltransferases (HMT) join methyl groups to histone tails and modify how tightly a DNA molecule is wrapped around it. the tighter the less likely they are to be transcribed therefore they will not be expressed
• X linked recessive

  an affected female must have an affected father and the trait will be passed on to her sons
• X linked dominant

  an affected male will pass the trait to all his daughters but not his sons
• Generations represented

  P = parental generation

  F1 = offspring of P

  F2 = offspring of F1
• Dihybrid cross


  look at the inheritance of two genes at the same time

  FOIL method - first, outside, inside, last

  always have a phenotypic ratio of 9:3:3:1
• What is it meant by "Linked genes"?

  that the genes are located closely on the same gene.

  there is a very small chance that they will be separated during the crossing over in prophase 1

  the effect of linkage is that it reduces the genetic variation of offspring