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
- Homozygous genetic cross results in all offspring being heterozygous
- Heterozygous genetic cross results in mix of homozygous and heterzygous offspring
- Codominance = when both alleles are dominant so both are expressed --> blood types A and B (heterozygous is AB) and snapdragon white and red flowers (heterozygous is pink)
- Multiple genes = when characteristic has more than two alleles (blood type has A, B and O)
- Sex chromosomes --> females have XX but males have XY
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Sex linkage = Y chromosome considerably shorter and don't have all the same genes as X so sometimes whatever allele is on the X is expressed if dominant or recessive <-- characteristic is classed as sex linked
- Colour blindness
- Haemophilia (slow blood clotting due to absence of blood clotting factor) if male gets the recessive gene on the X they won't have the corresponding dominant one so will get haemophilia. Heterozygous females = carriers
