The sum total of all observable features of an organism is?

1. Analyze the question The question asks for the term that describes all the observable (visible) features of an organism, such as height, skin colour, eye colour, blood group expression and so on.

2. Explain the concept

• Phenotype: the observable physical, physiological and behavioural characteristics of an organism. It results from the genotype interacting with the environment.
• Genotype: the genetic makeup of an organism, meaning the alleles it carries. It is not directly observable.
• Homozygous: having two identical alleles for a gene (e.g. TT or tt).
• Heterozygous: having two different alleles for a gene (e.g. Tt).

3. Solution, step by step

• The key phrase is "observable features", which means features you can see or measure.
• Genotype is the genetic code, which you cannot see, so C is out.
• Homozygous and heterozygous describe allele combinations, not features, so B and D are out.
• Only phenotype means the sum of the observable characteristics.

4. Answer The correct option is A. phenotype.

5. Tip Link the words: Phenotype = Physical appearance. Genotype = Genes. Phenotype = Genotype + Environment. A tall plant (phenotype) may carry the genotype Tt (heterozygous).