IB Biology Topic D3.2.4 Phenotype Revision Notes…

Phenotype Is the Set of Observable Traits an Organism Shows

Definition

Phenotype

The phenotype of an organism refers to its observable traits or characteristics, which result from the interaction between its genetic makeup (genotype) and the environment.

Traits can be structural (eye colour), functional (blood clotting speed), or behavioural (the language a person speaks).
Some traits are purely genetic, but many result from the interaction between genes and the environment.

Tip

Traits set solely by genotype are useful in forensic science because they stay fixed for life.

Traits Fall Into Three Groups by What Determines Them

A trait can be set by genotype alone, by the environment alone, or by both together.

Genotype Only	Environment and Genotype	Environment Only
Eye color—brown or blue/grey	Height in humans	Scars from surgery or wounds
ABO blood group	Skin color (affected by sun exposure)	River blindness (caused by environmental parasites)
Haemophilia—blood slow to clot	Diabetes (affected by lifestyle and genetics)	Language or accent

Theory of Knowledge

How does the idea of phenotype challenge a strict nature-versus-nurture divide?
Are there traits where one factor clearly dominates, or is it usually a mix?

Most Traits Come From Genes and Environment Together

Most traits arise from the interaction of genotype and environment.
1. Height: genes set the possible range, but childhood nutrition decides the final height.
2. Skin colour: genes set the baseline, but sun exposure adjusts the visible tone, an example of phenotypic plasticity covered in D3.2.6.
3. Diabetes: shaped by both a genetic predisposition and lifestyle.

Active recall

How does phenotype differ from genotype?
Give one trait set by genotype only and one set by environment only.
Why is human height classed as a trait shaped by both genotype and environment?

Phenotype Is the Set of Observable Traits an Organism Shows

Definition

Phenotype

The phenotype of an organism refers to its observable traits or characteristics, which result from the interaction between its genetic makeup (genotype) and the environment.

Traits can be structural (eye colour), functional (blood clotting speed), or behavioural (the language a person speaks).
Some traits are purely genetic, but many result from the interaction between genes and the environment.

Tip

Traits set solely by genotype are useful in forensic science because they stay fixed for life.

Traits Fall Into Three Groups by What Determines Them

A trait can be set by genotype alone, by the environment alone, or by both together.

Genotype Only	Environment and Genotype	Environment Only
Eye color—brown or blue/grey	Height in humans	Scars from surgery or wounds
ABO blood group	Skin color (affected by sun exposure)	River blindness (caused by environmental parasites)
Haemophilia—blood slow to clot	Diabetes (affected by lifestyle and genetics)	Language or accent

Theory of Knowledge

How does the idea of phenotype challenge a strict nature-versus-nurture divide?
Are there traits where one factor clearly dominates, or is it usually a mix?

Most Traits Come From Genes and Environment Together

Most traits arise from the interaction of genotype and environment.
1. Height: genes set the possible range, but childhood nutrition decides the final height.
2. Skin colour: genes set the baseline, but sun exposure adjusts the visible tone, an example of phenotypic plasticity covered in D3.2.6.
3. Diabetes: shaped by both a genetic predisposition and lifestyle.

Active recall

How does phenotype differ from genotype?
Give one trait set by genotype only and one set by environment only.
Why is human height classed as a trait shaped by both genotype and environment?

IB Biology Topic D3.2.4: Phenotype Notes

IB Biology Topic D3.2.4: Phenotype Notes

Phenotype Is the Set of Observable Traits an Organism Shows

Traits Fall Into Three Groups by What Determines Them

Most Traits Come From Genes and Environment Together

Phenotype Is the Set of Observable Traits an Organism Shows

Traits Fall Into Three Groups by What Determines Them

Most Traits Come From Genes and Environment Together

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

IB Biology Topic D3.2.4: Phenotype Notes

A - Unity and Diversity

B - Form and Function

C - Interaction and Interdependence

D - Continuity and Change

IB Biology Topic D3.2.4: Phenotype Notes

Phenotype Is the Set of Observable Traits an Organism Shows

Traits Fall Into Three Groups by What Determines Them

Most Traits Come From Genes and Environment Together

Phenotype Is the Set of Observable Traits an Organism Shows

Traits Fall Into Three Groups by What Determines Them

Most Traits Come From Genes and Environment Together