Variation and inheritance

• Chlorosis= cells are not producing the normal amount of chlorophyll.

  • Lack of chlorophyll reduces the ability of the plant to make food by photosynthesis.
• Environmental factors affecting chlorosis:


  • Light= in absence of light, plants will turn off their chlorophyll production to conserve resources.
  • Mineral deficiencies= lack of iron or magnesium. Iron is needed as a cofactor by some of the enzymes that make chlorophyll, magnesium found in chlorophyll molecule. If these elements are lacking, plant cant make chlorophyll and gradually leaves will turn yellow.
  • Virus infection= virus interfere with the metabolism of cells.
• Animal body mass 


  • Animals body mass is determined by a combination of both genetic and environmental factors.
  • Obesity or severely underweight are a result of environmental factors. Eg: amount of food eaten, quantity of exercise, presence of a disease.
  • Obesity can be a result of the genotype. Mutation on chromosome 7 causes the pattern of fat deposition to be altered.
  • This gene acts in conjunction with other genes which regulate the energy balance of the body. (Study mice possessing mutation grow 35-50% fatter by middle age)
• Genetic variation 


  • Created by the versions of genes you inherit.
  • Number of different alleles or variants.,
  • Combination of alleles is determined by sexual reproduction (meiosis) random fusion of gametes, crossing over, independent assortment.
• Genotype= genetic make-up of an organism.
• Phenotype= physical characteristics displayed.

  • Actual characteristics often influenced by the environment.
• Dominant allele= the version of the gene that will always be expressed.
• Recessive allele= will only be expressed if two copies of the allele as present.
• homozygous= have 2 identical alleles for a characteristic, can be homozygous dominant or recessive.
• Heterozygous= have 2 different alleles for a characteristic, dominant phenotype will be expressed.
• Discontinuous variation= individuals fall into distinct categories, normally only one gene in involved and little effect from the environment.
• Continuous variation= many genes involved, environment has a large effect.