GCSE · Biology · AQA · Spec 8461

Variation

Your blood group came from your parents, your accent from where you grew up, and your height from both. Many differences between living things are like your height.

Causes of variation

Where does each difference come from?

Individuals differ in all of these. For each one, tick what causes the differences: the genes an individual inherited, the environment it developed in, or both. If you think both, tick both.

A Genetic causes: the genes inherited from parents
B Environmental causes: the conditions an individual develops in

Human blood group (A, B, AB or O)
A scar left by an injury
How tall a person grows
Purple or white flowers on a pea plant
Body mass of an adult
The accent a person speaks with
How tall a sunflower grows
Natural eye colour
How much milk a dairy cow produces

Same genes, different conditions

Cuttings taken from one plant grow into new plants with exactly the same genes as the parent.

A gardener takes two cuttings from the same plant, so the two new plants have identical genes. One grows in a sunny bed with plenty of water. The other grows in deep shade in dry soil. After a few months, what will the two plants be like?

Write it, then mark it

Describe it in your own words

Describe how an organism's genome and its environment together influence its phenotype. [3 marks]

Your answer

0 words · your answer stays on this page and is not sent anywhere.

The mark scheme

The genome (the genes inherited) sets which characteristics can develop, or the limits of how they can develop. (1 mark)
The environment (the conditions during development, such as diet, light or water) affects how those characteristics actually develop. (1 mark)
The phenotype comes from the two acting together, so organisms with the same genes can have different phenotypes in different conditions. (1 mark)
A correct example of a characteristic affected by both, such as human height (genes plus diet) or plant height (genes plus light). (1 mark)

Model answer

The genome is the genetic material an organism inherits, and it sets what characteristics the organism can develop, for example how tall a person could grow. The environment an organism develops in, such as its diet, affects how those characteristics actually develop. The phenotype is the result of both together, so a person with the genes to be tall may not reach that height if they are poorly fed while growing.

Genome: what can develop. Environment: what does develop. Phenotype: the result of both.

Mutations and variants

What does a mutation do?

Individuals in a species carry slightly different versions of their genes, called variants. A mutation is a change in a gene. Variants and mutations are linked.

Which is closest to what you think right now?

Every mutation changes how an organism looks or works.Mutations are nearly always harmful to the organism.All variants come from mutations. Most have no effect on the phenotype, some influence it and very few determine it.Variants come from mixing two parents' genes, not from mutations.

How sure are you?

I'm sureI think soI'm guessing

Every mutation changes how an organism looks or works.

This is a common misconception

Most mutations have no effect on the phenotype at all. The organism looks and works exactly as it would have done without the change. Only some mutations influence the phenotype, and very few determine it.

Mutations are nearly always harmful to the organism.

This is a common misconception

Most mutations have no effect on the phenotype, so most of them make no difference to the organism. A mutation that does change the phenotype is the exception, not the rule.

All variants come from mutations. Most have no effect on the phenotype, some influence it and very few determine it.

This matches the evidence

Yes. Every variant first arose as a mutation. Most have no effect on the phenotype. Some influence it, adding a small push alongside other genes and the environment, the way many things together affect height. Very few determine a characteristic on their own, the way the genes for blood group do.

Variants come from mixing two parents' genes, not from mutations.

This is a common misconception

Inheriting genes from two parents passes on variants that already exist. It does not create new ones. Every one of those variants first arose as a mutation, at some point in the past.

All variants arise from mutations. Most have no effect on the phenotype, some influence it, and very few determine it.

From one mutation to a changed species

Reason it through

How can a mutation lead to a relatively rapid change in a whole species?

Link 1 of 4

First link · your turn

Mutations are not rare one-off events. How often do they happen, and what does that give a population?

Locked — reveal the link above first

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Sort everyday characteristics by what causes them, and watch the tidy two-box picture fall apart.

What you need to know

Variation is the differences in the characteristics of individuals in a population.
Variation may be due to differences in the genes inherited (genetic causes), the conditions in which individuals developed (environmental causes), or a combination of genes and the environment.
The genome and its interaction with the environment influence how an organism's phenotype develops.
There is usually extensive genetic variation within a population of a species.
All variants arise from mutations. Most have no effect on the phenotype, some influence the phenotype and very few determine it.
Mutations occur continuously. Very rarely a mutation leads to a new phenotype, and if the new phenotype suits an environmental change it can lead to a relatively rapid change in the species.

The big picture

Variation is the differences in characteristics between individuals in a population. It comes from the genes inherited, the conditions an individual develops in, or both together: the genome sets what can develop and the environment influences what does. A population usually carries extensive genetic variation. All variants arise from mutations, which occur continuously; most have no effect on the phenotype, some influence it and very few determine it. Very rarely a mutation leads to a new phenotype, and if it suits an environmental change the species can change relatively rapidly.

Key points

1Many characteristics are not genetic OR environmental: they sit in the overlap, caused by genes and the environment acting together.

2Organisms with identical genes can still develop different phenotypes if they grow in different conditions.

3The environment changes how an organism develops, not the genes it carries.

4Mutations are not rare and are not usually harmful: they happen all the time, and most change nothing in the phenotype.

5A new phenotype changes a species relatively quickly only if it suits a change in the environment.

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Worked example

Problem

Identical twins develop from one fertilised egg, so they inherit the same genes. As adults, one twin is 6 cm taller than the other, and only that twin has a scar on one arm. Both twins have blood group O. Explain what caused (a) the difference in height between the twins, (b) the scar, and (c) the twins having the same blood group.

⚠ Watch out

Forcing every characteristic into either 'genes' or 'environment'. Many characteristics, such as height and body mass, are caused by both acting together. A second slip is writing that most mutations are harmful: most mutations have no effect on the phenotype at all.

🧠

Memory hook

Genes deal the cards; the environment plays the hand. And for mutations: most do nothing, some nudge, very few decide.

✓

Check yourself

From memory: name the three causes of variation with an example of each, say what the genome and the environment each do, and finish 'most mutations…, some…, very few…'.

Flashcards

(12)

What is variation?

The differences in the characteristics of individuals in a population.

What are the three possible causes of variation?

Differences in the genes inherited (genetic), in the conditions an individual developed in (environmental), or a combination of genes and the environment.

Give two characteristics caused by genes and the environment together.

Any two of: human height, body mass, how tall a plant grows, a cow's milk yield.

What is a genome?

All of the genetic material of an organism.

What is a phenotype?

The characteristics an organism actually develops.

How do the genome and the environment each affect the phenotype?

The genome sets what can develop; the environment influences what actually develops.

Two plants have identical genes but grow in different conditions. Can their phenotypes differ?

Yes. The conditions change how each plant develops, even though the genes are the same.

How much genetic variation is there usually within a population of a species?

Usually extensive genetic variation.

Where do all variants come from?

Mutations.

How do mutations affect the phenotype?

Most have no effect, some influence it, and very few determine it.

How often do mutations occur, and how often do they lead to a new phenotype?

Mutations occur continuously, but only very rarely does one lead to a new phenotype.

When can a new phenotype lead to a relatively rapid change in a species?

When the new phenotype is suited to a change in the environment.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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Where does each difference come from?

Describe it in your own words

What does a mutation do?

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