• Variation plays an important role in evolution and forms the basis of natural selection.
• Natural selection is an evolutionary force that selects beneficial genes and removes the non-beneficial ones from the natural environment.
• Through natural selection, species that possess phenotypes which enable them to adapt to their surrounding will continue to live and breed for the survival of the species

• Enables natural environment to continue selecting beneficial characteristics and remove the non-suitable one.
• Enables survival of the species when the environment changes.
• Allows cross breeding among species to from new species.

• The differences in a character are not distinctive.
• Characters are quantitative; can be measured.
• Shows a normal distribution; exhibits intermediate characters.
• Influenced by environmental factors and controlled by two or more genes for the same character.
• The phenotype controlled by many pairs of alleles.
• Example: height, body weight, skin colour.

• The differences in a character are distinctive.
• Characters are qualitative; cannot be measured.
• Exhibits distinctive characters with no intermediates.
• Not influenced by environmental factors and controlled by a single gene that determines the differences between characters.
• The phenotype controlled by a pair of allele.
• Example: blood group, fingerprints.

Shows differences in characteristics among individuals of the same species.

• Organisms of the same species differ in terms of morphology, physiology and genetics.

• Environmental factors:
  • Temperature.
  • Light.
  • pH.

• Cross -linking during meiosis, independent selection during meiosis and random fertilization.
• Gene mutations (permanent changes in the nucleotide sequence) caused by physical/chemical mutating agents.
• Chromosome mutations: an increase or decrease in the number of chromosomes or changes to the structure of chromosomes.
• Types of chromosomal mutations: truncation, translocation, duplication and inversion.
• May cause genetic disorders; Turner syndrome, Down syndrome, trisomy X and Klinefelter syndrome.

• Includes abiotic factors; temperature, light intensity, humidity, nutrition and soil fertility.
• However, environmental factors cannot change the phenotype more than what has been predetermined by the genotype.
• Examples:
  • The flowering plant (Hydrangea sp.); produces blue flowers when the soil is acidic but pink flowers in alkaline soil.
  • Well-nourished one identical twin becomes heavier and bigger, while poorly nourished twin becomes smaller and lighter. 

• Hydrangea sp. plant produces blue flowers in acidic soil (pH less than 5.5) and pink flowers in alkaline soil.

• Siamese cat inherited the gene which produces dark pigment enzyme for fur colour.
• This enzyme only functions at temperature less than the body temperature.
• Parts of the body with lower temperature are the ears, face, tail and paws.
• Therefore, these body parts are dark in colour.

• Sunlight can alter skin colour.
• People who are under the sun for a long period of time will have tanned skin.
• For example, a construction worker.
• Ultraviolet rays in sunlight can destroy melanin pigment of exposed skin.
• Therefore, more melanin pigment will be produced, which cause the skin to be darker.

• Before industrialisation and the environment is not polluted, the grey-coloured moth population is higher than the other one because they can be camouflaged by the lichen-covered tree trunk.
• Meanwhile, dark melanic moth dies easily, which eaten by predators because they cannot camouflage.
• After industrialisation, the grey-coloured moth dies because they cannot camouflage as the pollution kills the lichen-covered three trunks.
• Meanwhile, dark melanic population increases as they can be camouflaged by the polluted environment.
• In such a case, the phenotype of the organism affects its chances of survival.

• Variation plays an important role in evolution and forms the basis of natural selection.
• Natural selection is an evolutionary force that selects beneficial genes and removes the non-beneficial ones from the natural environment.
• Through natural selection, species that possess phenotypes which enable them to adapt to their surrounding will continue to live and breed for the survival of the species

• Enables natural environment to continue selecting beneficial characteristics and remove the non-suitable one.
• Enables survival of the species when the environment changes.
• Allows cross breeding among species to from new species.

• The differences in a character are not distinctive.
• Characters are quantitative; can be measured.
• Shows a normal distribution; exhibits intermediate characters.
• Influenced by environmental factors and controlled by two or more genes for the same character.
• The phenotype controlled by many pairs of alleles.
• Example: height, body weight, skin colour.

• The differences in a character are distinctive.
• Characters are qualitative; cannot be measured.
• Exhibits distinctive characters with no intermediates.
• Not influenced by environmental factors and controlled by a single gene that determines the differences between characters.
• The phenotype controlled by a pair of allele.
• Example: blood group, fingerprints.

Shows differences in characteristics among individuals of the same species.

• Organisms of the same species differ in terms of morphology, physiology and genetics.

• Environmental factors:
  • Temperature.
  • Light.
  • pH.

• Cross -linking during meiosis, independent selection during meiosis and random fertilization.
• Gene mutations (permanent changes in the nucleotide sequence) caused by physical/chemical mutating agents.
• Chromosome mutations: an increase or decrease in the number of chromosomes or changes to the structure of chromosomes.
• Types of chromosomal mutations: truncation, translocation, duplication and inversion.
• May cause genetic disorders; Turner syndrome, Down syndrome, trisomy X and Klinefelter syndrome.

• Includes abiotic factors; temperature, light intensity, humidity, nutrition and soil fertility.
• However, environmental factors cannot change the phenotype more than what has been predetermined by the genotype.
• Examples:
  • The flowering plant (Hydrangea sp.); produces blue flowers when the soil is acidic but pink flowers in alkaline soil.
  • Well-nourished one identical twin becomes heavier and bigger, while poorly nourished twin becomes smaller and lighter. 

• Hydrangea sp. plant produces blue flowers in acidic soil (pH less than 5.5) and pink flowers in alkaline soil.

• Siamese cat inherited the gene which produces dark pigment enzyme for fur colour.
• This enzyme only functions at temperature less than the body temperature.
• Parts of the body with lower temperature are the ears, face, tail and paws.
• Therefore, these body parts are dark in colour.

• Sunlight can alter skin colour.
• People who are under the sun for a long period of time will have tanned skin.
• For example, a construction worker.
• Ultraviolet rays in sunlight can destroy melanin pigment of exposed skin.
• Therefore, more melanin pigment will be produced, which cause the skin to be darker.

• Before industrialisation and the environment is not polluted, the grey-coloured moth population is higher than the other one because they can be camouflaged by the lichen-covered tree trunk.
• Meanwhile, dark melanic moth dies easily, which eaten by predators because they cannot camouflage.
• After industrialisation, the grey-coloured moth dies because they cannot camouflage as the pollution kills the lichen-covered three trunks.
• Meanwhile, dark melanic population increases as they can be camouflaged by the polluted environment.
• In such a case, the phenotype of the organism affects its chances of survival.