patterns of inheritance and variation

• Phenotype


  Genotype + Environment
• Genes


  2+ forms and separate -> Alleles
• Chlorosis


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


  • Lack of light -> Turn off chlorophyll production (conserve resources)
  • Mineral deficiencies (e.g. lack of iron + magnesium)
  • Iron - Cofactor for chlorophyll production enzymes
  • Magnesium - Found in chlorophyll molecule
  • Virus infections -> Interfere with metabolism
• Obesity


  • Energy imbalance from calories consumed + burnt
  • 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


  • Characteristic that can take any value within a range
• Discontinuous variation


  • Characteristic that can only appear in discrete values
• Continuous variation


  Genetic + environmental
• Discontinuous variation


  Mostly genetic
• Examples of continuous variation


  • Leaf surface area
  • Animal mass
• Examples of discontinuous variation

  • Blood group
  • Albinism
  • Skin color
• Continuous variation at genetic level

  • Different genes = Additive effect
  • Different alleles on same locus = Small effect
• Discontinuous variation at genetic level

  • Different genes = Different effect
  • Different alleles on same locus = Large effect

  
• Monogenic inheritance

  Trait determined by expression of single allele
• Monogenic inheritance 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 example

  • 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
  • Iᴬ -> Antigen A, Iᴮ -> Antigen B, Iᴼ no antigen
• Dihybrid inheritance

  1. Inheritance of two different characteristics

  2. Cross: 4x4 Punnett square

  3. Group alleles together (RrYy not RYry)

  4. 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 reduces -> Recombination frequency gets smaller
  • Degree of crossing over determined by proximity of genes
• Sex linkage

  • Genes on X chromosomes
  • Y chromosome smaller -> Do not have some genes
  • Trait caused by recessive allele on X
• Haemophilia

  • Sex linked genetic disorder
  • Slow clotting (no clotting factor 8)
  • 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
  • Hypostatic: Gene affected by another gene
  • Epistatic: Gene affects expression of another gene
  • Typical ratio 9:3:4
• Epistasis example

  • Labrador colors: B (black), b (brown), E (pigment in skin and fur), e (pigment in skin only)
• Evolution

  Change in allele frequencies over time