patterns of inheritance

• Phenotype


  Genotype + Environment
• Genes


  2+ forms and separate -> Alleles
• Chlorosis


  When leaves are pale/yellow
• Not enough chlorophyll produced -> Limits photosynthesis
• Environmental factors causing chlorosis


  • Lack of light -> Turn off chlorophyll production (conserve resources)
  • Mineral deficiencies (e.g. lack of iron + magnesium)
  • Virus infections -> Interfere with metabolism
• Iron


  Cofactor for chlorophyll production enzymes
• Magnesium


  Found in chlorophyll molecule
• Obesity


  Energy imbalance from calories consumed + burnt
• Obesity is a combination of both gene + environment
• Obese mice


  Mutation on chromosome 7 -> Pattern of fat deposition changes, Grows 35-50% fatter
• Dominant allele


  Gene always expressed if present
• Recessive allele


  Required 2 copies of allele to be expressed
• Homozygous


  Two identical alleles
• Heterozygous


  Two different alleles
• Continuous variation


  A characteristic that can take any value within a range
• Discontinuous variation


  A characteristic that can only appear in discrete values
• Continuous variation is caused by genetic + environmental factors, while discontinuous variation is mostly genetic
• Genetic control of continuous variation

  Polygenes - number of genes
• Genetic control of discontinuous variation


  One or two genes
• Continuous variation


  • Leaf surface area
  • Animal mass
• Discontinuous variation


  • Skin color
  • Blood group
  • Albinism
• Genetic level of continuous variation


  • Diff genes = additive effect
  • Diff alleles on same locus = small effect
• Genetic level of discontinuous variation


  • Diff genes = diff effect
  • Diff alleles on same locus = large effect
• Monogenic inheritance


  Trait determined by expression of single allele
• Genetic cross


  1. State phenotype of both parents

  2. State genotype (same gene same letter)

  3. State gametes for each parent

  4. Punnett square

  5. State proportion of each genotype produced (ratio)

  6. State corresponding phenotype (percentage)
• F1


  First generation
• F2


  Offspring from F1 produce offspring
• Codominance


  2 different alleles occur for a gene both are dominant, both expressed in phenotype
• Codominance


  • Snapdragon flower colour: Red flower (CᴿCᴿ), White flower (CᵂCᵂ), Pink flower (CᴿCᵂ)
• Multiple alleles


  Gene I (immunoglobulin) - production of different antigen on RBC: IᴬIᴮ codominant, Iᴼ recessive
• Dihybrid inheritance


  Inheritance of two different characteristics
• Dihybrid cross


  1. Cross: 4x4 Punnett square

  2. Group alleles together (RrYy not RYry)

  3. Typical ratio 9:3:3:1
• Autosomal linkage


  When 2+ genes located on the same autosome, less likely to be separated during crossing over -> inherited together
• Recombinant frequency


  • # of recombinant offspring / total # of offspring
  • x<50% = no linkage
  • x>50% = gene linkage
• Degree of crossing over


  Determines recombination frequency, smaller with closer proximity of genes
• Sex linkage

  X chromosomes are larger

  Y chromosome smaller -> do not have some genes and would mean have recessive illnesses
• Sex linked disorder

  • Haemophilia - slow clotting of blood (no clotting factors)
  • only men have this due to the Y chromosome being smaller
• Haemophilia genotypes


  Xᴴ: dominant healthy allele, Xʰ: recessive faulty allele, Y: no allele
• Chi squared test


  Measures size of difference between observed and expected values, df = (# of categories) - 1
• Epistasis


  Interaction between 2 non-linked structural genes which causes 1 gene to mask expression of other in phenotype