Variation and inheritance

Chlorosis

• Chlorosis = when plants aren't producing enough chlorophyll so look pale and yellow --> reduces plant's ability to photosynthesise
• Most plants showing chlorosis have the right genes for chlorophyll but its influenced by environmental factors :
  • Lack of light --> plants turn off chlorophyll production to not waste resources
  • Mineral deficiencies --> lack of iron or magnesium (iron is cofactor for some enzymes for making chlorophyll and magnesium is used in the chlorophyll molecule)
  • Virus infections --> viruses interfere with the metabolism of cells, infected tissues no longer support chlorophyll synthesis

Animal body mass

• Determined by a mix of genes and environment
• Environment --> overfeeding or underfeeding, lack of exercise, presence of disease
• Genetic --> pattern of fat deposition can be altered

Creating genetic variation

• Created by versions of genes inherited from parents
• Individual mixture of alleles influences the characteristics shown
• Combination generated by meiosis and random fusion of gametes
• Genotype = combination of alleles inherited for characteristic
• Phenotype = observable characteristics of organism
• Actual characteristics displayed also controlled by environment
• Dominant alleles are always expressed
• Recessive alleles only expressed if there's two of them
• Homozygous = two identical alleles for the characteristic
• Hetereozygous = two different alleles for the characteristic (only the dominant one is expressed)

Continuous and discontinuous variation

• Continuous = characteristic that can take any value within a range, caused by genetics and environment, controlled by a number of genes --> leaf surface area and animal mass
• Discontinuous = characteristic that can only appear in distinct categories, caused by genetics, controlled by one or two genes --> blood group, round and wrinkled pea shape