Inheritance Patterns
1. Traits and Variation
Learning outcomes
-
I can define inherited and acquired traits.
- I can explain how variation occurs within populations.
- I can distinguish between genetic and environmental influences on traits.
- I can identify examples of inherited traits.
- I can explain why variation is important in populations.
What Is a Trait?
A trait is a characteristic or feature of an organism.
Traits can include characteristics such as:
- eye colour
- blood type
- height
- hair characteristics
- flower colour
- leaf shape
- body size
- behaviour
- ability to perform particular activities
Some traits are strongly influenced by:
genes.
Others are strongly influenced by:
the environment.
Many traits are influenced by:
both genes and the environment.
What Are Inherited Traits?
An inherited trait is a characteristic influenced by genetic information passed from parents to:
offspring.
Genes are sections of:
DNA.
During reproduction, genetic information is passed from one generation to the:
next.
This is called:
inheritance.
Examples of strongly inherited human characteristics include:
- blood group
- natural eye colour
- some aspects of hair colour
- some aspects of hair texture
- biological sex characteristics
- many inherited genetic conditions
Genes and Traits
A gene is a section of DNA containing information that can influence a biological:
characteristic.
Different versions of the same gene are called:
alleles.
An individual inherits alleles from biological:
parents.
The particular combination of alleles an organism possesses is part of its:
genotype.
The observable characteristics of an organism are called its:
phenotype.
Genotype and Phenotype
It is useful to distinguish between:
genotype
and:
phenotype.
Genotype refers to an organism's genetic makeup.
Phenotype refers to its observable characteristics.
A phenotype can be influenced by:
genotype, environment, or both.
A useful relationship is:
Genotype + Environment → Phenotype
This is a simplified model, but it helps explain why genetically similar individuals can sometimes look or behave:
differently.
What Are Acquired Traits?
An acquired trait is a characteristic that develops during an organism's lifetime because of:
environment, experience, behaviour, or use.
Acquired traits are not usually produced by changes to the DNA sequence that can be passed through gametes.
Examples include:
- a scar from an injury
- increased muscle size from exercise
- a suntan
- learning to play an instrument
- learning a language
- improved athletic skill through training
These characteristics develop because of what happens during the individual's:
lifetime.
Inherited vs Acquired Traits
| Inherited Traits | Acquired Traits |
|---|---|
| Influenced by genes inherited from parents | Develop during an individual's lifetime |
| Genetic information can be passed through reproduction | Usually not passed genetically to offspring |
| Present because of inherited DNA | Often caused by environment, experience or behaviour |
| Example: blood type | Example: scar |
| Example: natural eye colour | Example: learned language |
The key question is:
Was the characteristic inherited genetically, or did it develop because of the individual's experiences or environment?
An Important Misconception
Suppose a person develops very large muscles through:
exercise.
Their children will not automatically inherit those enlarged muscles.
The person's muscle development is an:
acquired characteristic.
The children may inherit genes that influence characteristics such as body structure or potential muscle development, but they do not inherit the parent's:
exercise-produced muscles.
Genetic Influences
Some variation occurs because individuals have different:
genetic information.
Genetic differences can arise through:
- inheritance of different alleles
- meiosis
- crossing over
- independent assortment
- random fertilization
- mutation
These processes contribute to:
genetic variation.
Environmental Influences
The environment can also affect an organism's:
phenotype.
Environmental influences include:
- nutrition
- temperature
- sunlight
- water availability
- physical activity
- disease
- education
- living conditions
These influences can cause differences between individuals even when their genetic information is:
similar.
Example: Nutrition and Growth
Genes influence a person's potential:
height.
However, growth can also be affected by:
nutrition and health.
Two individuals with similar genetic potential may reach different adult heights if they experience very different conditions during:
development.
Therefore, height is influenced by:
both genes and environment.
Example: Plant Growth
Consider two genetically similar plants.
Plant A receives:
- plenty of light
- sufficient water
- adequate minerals
Plant B receives:
- little light
- limited water
- poor mineral supply
The plants may develop very different:
phenotypes.
Plant A may become taller and healthier than Plant B even though their genetic information is very:
similar.
Example: Skin Pigmentation and Sunlight
A person's genes influence their natural:
skin pigmentation.
Exposure to sunlight can also increase production of:
melanin,
causing tanning.
Therefore, observed skin pigmentation can be influenced by:
both genetic and environmental factors.
A suntan itself is an:
acquired characteristic.
Traits Influenced by Both Genes and Environment
Many traits cannot be classified as purely genetic or purely:
environmental.
Examples can include:
- height
- body mass
- athletic performance
- some aspects of behaviour
- risk of many diseases
- plant growth
- milk production in cattle
- crop yield
These traits result from interactions between:
genes and environmental conditions.
Continuous Variation
Some characteristics can take many values across a:
range.
This is called:
continuous variation.
Examples include:
- height
- body mass
- hand span
- foot length
- plant height
If we measured the heights of hundreds of people, we would find many values rather than only a few:
categories.
Why Does Continuous Variation Occur?
Continuous variation is often influenced by:
many genes.
It can also be strongly influenced by:
environmental factors.
For example, human height is influenced by genetic factors, but also by conditions such as:
nutrition and health during development.
This produces a wide range of:
phenotypes.
Discontinuous Variation
Some characteristics fall into clear:
categories.
This is called:
discontinuous variation.
A classic example is:
ABO blood group.
People belong to one of the categories:
A, B, AB, or O.
There are no intermediate ABO blood groups between:
A and B.
Continuous vs Discontinuous Variation
| Continuous Variation | Discontinuous Variation |
|---|---|
| Many possible values | Distinct categories |
| Usually measured | Usually counted or classified |
| Often influenced by many genes | Often controlled by fewer genes |
| Environment may have a strong influence | Often more strongly genetic |
| Example: height | Example: ABO blood group |
What Is Variation?
Variation means differences between individuals.
Look at members of almost any species and you will notice that they are not completely:
identical.
Humans vary in characteristics such as:
- height
- blood group
- facial features
- hair characteristics
- body proportions
Plants can vary in:
- height
- flower colour
- leaf size
- growth rate
- disease resistance
Variation occurs throughout:
populations.
What Is a Population?
A population is a group of organisms of the same species living in the same area at the same:
time.
Individuals within a population usually show:
variation.
Some variation is genetic.
Some is environmental.
Much variation results from:
both.
Why Aren't Individuals Genetically Identical?
In sexually reproducing organisms, offspring receive genetic information from:
two parents.
Meiosis creates different combinations of chromosomes and:
alleles.
During meiosis:
crossing over creates new combinations of alleles.
Independent assortment distributes chromosomes into gametes in different combinations.
Then:
random fertilization combines different gametes.
These processes create enormous genetic:
variation.
Mutation and Variation
Another source of genetic variation is:
mutation.
A mutation is a change in:
DNA.
Mutations can produce new:
alleles.
Most genetic reshuffling during sexual reproduction rearranges existing alleles, while mutation can introduce:
new genetic variants.
Are Mutations Always Harmful?
No.
A mutation may be:
- harmful
- neutral
- beneficial
Its effect can also depend on the:
environment.
A genetic variant that provides little advantage under one set of conditions might become useful if conditions:
change.
Variation Within a Species
Members of the same species share many:
characteristics.
However, they are not necessarily identical.
For example, members of a plant species may differ in:
- height
- flower size
- resistance to disease
- tolerance to drought
- growth rate
These differences represent variation within the:
species.
Why Is Variation Important?
Variation is important because environmental conditions can:
change.
Populations may experience:
- new diseases
- changing temperatures
- drought
- floods
- new predators
- new competitors
- changing food supplies
If every individual were genetically identical, they might all respond similarly to a new:
challenge.
Variation and Survival
Suppose a population of plants experiences a severe:
drought.
Some plants may possess inherited characteristics that allow them to:
- conserve water more effectively
- develop deeper roots
- tolerate dehydration
- reduce water loss
These plants may be more likely to survive and:
reproduce.
Variation means that individuals do not all respond to environmental challenges in exactly the same:
way.
Variation and Disease
Imagine a population exposed to a new:
pathogen.
If there is genetic variation, some individuals may be more resistant to the pathogen than:
others.
Those individuals may have a greater chance of surviving and:
reproducing.
Their alleles can then be passed to the next:
generation.
Variation and Natural Selection
Natural selection occurs when inherited differences affect survival and reproductive success in a particular:
environment.
A simplified sequence is:
Variation exists in a population
↓
Environmental pressures affect individuals differently
↓
Some individuals survive and reproduce more successfully
↓
Their inherited alleles are passed to offspring
↓
Allele frequencies in the population can change over generations
Variation therefore provides the raw material for:
natural selection.
Variation Does Not Occur Because Organisms Need It
A common misconception is that organisms develop useful inherited traits because they:
need them.
For example, a population does not encounter drought and then deliberately produce genes for:
drought resistance.
Instead:
variation already exists or arises through mutation.
Environmental conditions then influence which variants are more likely to be passed to future:
generations.
Acquired Traits and Natural Selection
Natural selection depends on characteristics that can be:
inherited.
Suppose an animal becomes stronger through exercise.
That increased muscle size is largely an:
acquired characteristic.
The muscles themselves are not genetically passed to:
offspring.
Therefore, natural selection operates on inherited genetic variation rather than simply on changes acquired during an individual's:
lifetime.
Identical Twins and Environment
Identical twins provide a useful example of genetic and environmental:
influences.
Identical twins begin with nearly identical genetic:
information.
However, they can develop differences because of:
- diet
- exercise
- illness
- experiences
- environmental exposures
This demonstrates that phenotype is not determined by genes:
alone.
Genes Set Possibilities, Not Always Fixed Outcomes
For many traits, genes influence a range of possible:
outcomes.
The environment influences how those genetic tendencies are:
expressed.
For example, genes may contribute to the potential for tall growth.
However, severe nutritional deficiencies during development may prevent a person from reaching that:
potential.
Environmental Variation Is Not Necessarily Inherited
Suppose two plants are genetically identical.
One receives plenty of water and grows:
large.
The other receives very little water and remains:
small.
The difference in size is largely caused by:
environmental conditions.
Seeds or offspring from the smaller plant do not automatically inherit its environmentally caused:
small size.
Real-World Example: Crop Plants
Farmers often grow crop varieties with particular inherited:
traits.
Useful traits may include:
- high yield
- disease resistance
- drought tolerance
- large fruits
- rapid growth
However, crop performance also depends on:
environmental conditions.
Even a genetically high-yielding crop may perform poorly without sufficient:
water, minerals, or suitable temperature.
Real-World Example: Animal Breeding
Humans have selected animals for inherited characteristics for:
thousands of years.
Examples include selecting animals for:
- milk production
- body size
- wool characteristics
- behaviour
- speed
This process is called:
selective breeding.
It works because populations contain:
inherited genetic variation.
Real-World Example: Antibiotic Resistance
Bacterial populations can contain genetic:
variation.
Some bacteria may possess mutations that provide resistance to a particular:
antibiotic.
When the antibiotic is used, susceptible bacteria are more likely to die.
Resistant bacteria are more likely to:
survive and reproduce.
The antibiotic does not create resistance because the bacteria:
need it.
Instead, it creates a selective environment in which resistant variants have an:
advantage.
Comparing Genetic and Environmental Variation
| Genetic Variation | Environmental Variation |
|---|---|
| Caused by differences in genetic information | Caused by differences in environmental conditions |
| Can involve different alleles | Does not necessarily involve DNA differences |
| Can be inherited if present in reproductive cells | Usually not genetically inherited |
| Produced by mutation and genetic reshuffling | Produced by factors such as diet or temperature |
| Important in evolution | Can strongly influence phenotype |
Many characteristics involve:
both.
Worked Example: Blood Group
A person's ABO blood group is determined primarily by:
inherited alleles.
Changing diet, exercising, or spending more time in sunlight will not change someone's ABO:
blood group.
Therefore, ABO blood group is an example of strongly:
genetic variation.
Worked Example: Scar
A person develops a scar after:
injury.
The scar was not inherited from their:
parents.
It developed because of an environmental event during the person's:
lifetime.
Therefore, the scar is an:
acquired trait.
Worked Example: Height
Two people differ in:
height.
Can we immediately say the difference is entirely genetic?
No.
Height is influenced by genetic factors as well as environmental conditions such as:
nutrition and health.
Therefore, height demonstrates an interaction between:
genes and environment.
Worked Example: Plant Colour
Two genetically identical plants are grown under different light conditions.
One becomes pale while the other remains:
green.
If the difference results from the growing conditions, it represents:
environmental variation.
The plants can have similar genotypes but different:
phenotypes.
Inherited Does Not Mean Unchangeable
A trait can have a strong genetic component without being completely:
fixed.
For example, genes influence body size, but nutrition and activity can influence the final:
phenotype.
Therefore:
inherited does not necessarily mean unaffected by environment.
Environmental Does Not Mean Unimportant
Environmental influences can produce major differences in:
phenotype.
Nutrition can affect growth.
Sunlight can affect plant development.
Exercise can affect muscle size.
Temperature can affect growth and development in many:
organisms.
Genes and environment frequently:
interact.
Common Mistake: Every Trait Is Either Genetic or Environmental
Many traits are influenced by:
both.
Height is a good example.
Genes influence height, but so do:
nutrition, health, and developmental conditions.
It is often better to think about the relative contributions of genes and environment rather than forcing every trait into one:
category.
Common Mistake: All Inherited Traits Come from One Gene
Some characteristics are influenced primarily by:
one or a few genes.
Others are influenced by:
many genes.
Traits influenced by many genes are called:
polygenic traits.
Human height is an example of a highly:
polygenic characteristic.
Common Mistake: Variation Means Mutation
Mutation is one source of:
variation.
But genetic variation also comes from:
- crossing over
- independent assortment
- random fertilization
Environmental conditions can create phenotypic variation without changing:
DNA sequences.
Common Mistake: Acquired Characteristics Are Passed to Offspring
A characteristic developed during an individual's lifetime is not normally inherited genetically by:
offspring.
For example:
A scar is not inherited.
A suntan is not inherited.
Muscles developed through exercise are not inherited as enlarged muscles.
Inheritance depends on genetic information passed through:
reproduction.
Common Mistake: Variation Is Always Beneficial
Variation is not automatically:
beneficial.
A particular variant may be:
- advantageous
- disadvantageous
- neutral
Its effect depends partly on the:
environment.
Variation is important because it creates differences on which natural selection can:
act.
Check Your Understanding
1. Define a trait.
2. Define an inherited trait.
3. Define an acquired trait.
4. Give three examples of inherited traits.
5. Give three examples of acquired traits.
6. What is a gene?
7. What is an allele?
8. Define genotype.
9. Define phenotype.
10. Explain how genotype and environment can both influence phenotype.
11. Why is a scar considered an acquired characteristic?
12. Why is ABO blood group considered an inherited characteristic?
13. Explain why increased muscle size caused by exercise is not normally inherited.
14. Define variation.
15. What is a population?
16. Give three sources of genetic variation.
17. Explain how meiosis contributes to variation.
18. Explain how mutation contributes to variation.
19. Give three environmental factors that can affect phenotype.
20. Explain why height is influenced by both genes and environment.
21. Distinguish between continuous and discontinuous variation.
22. Give two examples of continuous variation.
23. Give one example of discontinuous variation.
24. Explain why variation is important when environmental conditions change.
25. Explain how genetic variation can affect a population exposed to disease.
26. Explain the relationship between variation and natural selection.
27. Why doesn't natural selection simply cause organisms to develop traits because they need them?
28. Two genetically similar plants are grown with different amounts of water. Explain why they may have different phenotypes.
29. Explain why inherited does not always mean completely determined by genes.
30. Explain why genetic variation is important for the long-term survival and evolution of populations.
Key Terms
- Trait: Characteristic or feature of an organism.
- Inherited trait: Characteristic influenced by genetic information passed from parents to offspring.
- Acquired trait: Characteristic developed during an organism's lifetime because of environment, experience, or behaviour.
- Inheritance: Transmission of genetic information between generations.
- Gene: Section of DNA that influences a biological characteristic or function.
- Allele: Alternative version of a gene.
- Genotype: Genetic makeup of an organism.
- Phenotype: Observable characteristics of an organism.
- Variation: Differences among individuals.
- Genetic variation: Variation caused by differences in genetic information.
- Environmental variation: Variation caused by differences in environmental conditions.
- Population: Group of organisms of the same species living in the same area at the same time.
- Continuous variation: Variation showing a range of possible values.
- Discontinuous variation: Variation consisting of distinct categories.
- Polygenic trait: Characteristic influenced by many genes.
- Mutation: Change in DNA.
- Crossing over: Exchange of DNA between homologous chromosomes during meiosis.
- Independent assortment: Distribution of chromosomes into different combinations during meiosis.
- Natural selection: Process in which inherited differences influence survival and reproductive success.
- Selective breeding: Human selection of organisms with desired inherited traits for reproduction.
Key Takeaways
- A trait is a characteristic of an organism.
- Inherited traits are influenced by genetic information passed from parents to offspring.
- Acquired traits develop during an individual's lifetime.
- Genes are sections of DNA that influence characteristics.
- Different versions of genes are called alleles.
- Genotype describes genetic makeup.
- Phenotype describes observable characteristics.
- Phenotype can be influenced by both genotype and environment.
- ABO blood group is an example of a strongly inherited trait.
- Scars, suntans, and learned skills are examples of acquired characteristics.
- Many traits cannot be described as entirely genetic or entirely environmental.
- Height is influenced by both genes and environmental conditions.
- Variation refers to differences among individuals.
- Variation can be genetic, environmental, or a combination of both.
- Meiosis contributes to genetic variation through crossing over and independent assortment.
- Random fertilization creates additional genetic combinations.
- Mutations can produce new genetic variants.
- Continuous variation produces a range of values.
- Height and body mass are examples of continuous variation.
- Discontinuous variation produces distinct categories.
- ABO blood group is an example of discontinuous variation.
- Genetic variation is important because individuals may respond differently to environmental change.
- Variation can help populations persist when diseases or environmental conditions change.
- Genetic variation provides the raw material for natural selection.
- Natural selection acts on existing inherited variation; organisms do not develop useful inherited traits simply because they need them.
- Acquired characteristics are not normally passed genetically to offspring.
- Variation is not automatically beneficial; a trait's effect depends on the environment.
- Genes and environment frequently interact to produce an organism's phenotype.
- Understanding traits and variation provides an important foundation for studying inheritance, natural selection, and evolution.