KS3 · Biology

Sexual reproduction and inheritance

You’re not a copy of your mum or dad, but you’re not a stranger either. So what actually gets handed down? Not the freckles. Something much smaller.

The inheritance chain

Four links, in order. Tap each one to see what it adds.

Process · Closed loop

A frog’s life cycle

A life cycle is the stages a living organism goes through in its life. Tap a stage and follow the loop round.

Stage 01

Frogspawn

A frog produces frogspawn. These are new living things, called offspring, and the start of this life cycle.

One parent or two?

Two parentsvsOne parent (bacteria)

Tap a row to see what it tells you. Start with where the genetic material comes from.

Focus

Where the genetic material comes from

Two parents

Half from each parent

One parent (bacteria)

From the one parent, which copies its DNA

The insight

This is the big difference. With two parents the offspring inherits half of its genetic material from each. A bacterium has only one parent, so the parent copies its DNA and the offspring gets that.

What happens in reproduction

Two parents

Chromosomes are passed from the parents to the offspring

One parent (bacteria)

The parent copies its DNA, the cell grows, then it divides to form offspring

Features inherited from

Two parents

Both parents, so the offspring look similar to both

One parent (bacteria)

Genetic material passed from the one parent

Is genetic material passed on?

Two parents

Yes

One parent (bacteria)

Yes

Which idea is closest to yours?

Same parents, not identical

Same parents, two daughters: similar, but not identical.

Two sisters have the same two parents. They look similar, but they are not identical. Which idea is closest to what you think?

Each sister takes after one parent: one is like Mum and the other is like Dad.They get the same genetic material from the same parents, so they should be identical.Each sister inherits a different combination of genetic material from the same two parents.A child is a perfect copy of the two parents mixed together, so a child is identical to its parents.

How sure are you?

I'm sureI think soI'm guessing

Each sister takes after one parent: one is like Mum and the other is like Dad.

This is a common misconception

It is an easy idea to believe, because people do say ‘you’ve got your dad’s nose’. But with two parents, each offspring inherits half of its genetic material from each parent, so it gets features from both. It is not a case of choosing one parent.

They get the same genetic material from the same parents, so they should be identical.

This is a common misconception

Same parents does not mean same combination. Each offspring of the same parents inherits a different combination of genetic material. That is why siblings look similar but are not identical: there is variation between them.

Each sister inherits a different combination of genetic material from the same two parents.

This matches the evidence

Yes. Half comes from each parent, so the sisters look alike (family resemblance). But each one gets a different combination, so there is variation between them.

A child is a perfect copy of the two parents mixed together, so a child is identical to its parents.

This is a common misconception

Children resemble their parents, but they are not identical to them. Inheriting half from each parent gives a combination of its own, and that is why there is variation.

Same two parents, but each offspring inherits a different combination of genetic material. So siblings are similar but not identical.

Now you explain it

Reproduction and inheritance, in your own words

Explain how reproduction is linked to inheritance. [4 marks]

Your answer

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

The mark scheme

Reproduction passes genetic material (DNA) from parent(s) to offspring. (1 mark)
The order of the DNA’s units gives instructions for the inherited features. (1 mark)
The DNA sits in chromosomes, which are what get handed on. (1 mark)
This is how the offspring end up with their parents’ features. (1 mark)

Model answer

Reproduction hands genetic material to the next generation. The DNA holds instructions for features, in the order of its units. It comes bundled in chromosomes, so the chromosomes go to the offspring, and that is how the offspring end up with their parents’ features.

Say what is passed on (genetic material, DNA), how it is packaged (chromosomes), and what the offspring end up with (the features of their parents).

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What really gets handed on from parents to offspring, and why it makes offspring look like their parents.

What you need to know

Reproduction is making new living things, called offspring, and every kind of living organism does it.
A life cycle is the stages an organism goes through in its life, and organisms reproduce at some point in it.
Offspring are the same kind as their parents. They resemble them at some point in the life cycle, frogspawn only later.
Features are inherited when genetic material (DNA) is passed from parents to offspring during reproduction.
Genetic material holds instructions for inherited features and for life processes such as growth and digestion.
Have a goYour classmate Jake announces, “My dad handed his features down to me.” He is almost right. What is actually handed on?
Genetic material (DNA), which holds the instructions for those features.
The features themselves are not what travels from parent to child. The genetic material is, and its instructions are what the inherited features come from.
DNA is a very long molecule made of units called A, T, C and G. Their order is the genetic code.
Have a goTwo stretches of DNA: A-T-T-C-G-A and G-A-T-C-A-T. Both use exactly the same units. Do they give the same instructions?
No. The order of the units is the genetic code, so a different order gives different instructions.
Having the same units is not enough. The genetic code is the order of the A, T, C and G units, not just which ones are there.
In animal, plant and fungal cells, DNA is stored in the nucleus, organised into chromosomes: big bundles of DNA.
With two parents, an offspring inherits half its genetic material from each, so it gets features from both.
Have a goDev says, “I got most of my genetic material from Mum, because I look like her.” Is he right?
No. With two parents he inherited half from each, so he has features from both.
With two parents, an offspring inherits half of its genetic material from each of them, however much it seems to look like one.
Each offspring of the same parents gets a different combination, so siblings look similar but are not identical.
Bacteria have one parent: it copies its DNA, the cell grows, then it divides, so genetic material is still passed on.

The big picture

Reproduction is how inheritance happens. Genetic material (DNA) carries the genetic code, it is packaged into chromosomes, and the chromosomes are passed to the offspring, so offspring inherit the features of their parents. With two parents, each gives half. Bacteria have one parent, which copies its DNA and passes it on.

Key points

1Reproduction makes new living things called offspring, and it is one of the common processes of all living organisms.

2Genetic material (DNA) carries the genetic code. It is packaged into chromosomes, which are passed to the offspring in reproduction.

3With two parents, offspring inherit half from each parent, but each gets a different combination, so siblings vary.

4Bacteria reproduce with one parent: the parent copies its DNA, grows, then divides.

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Worked example

Problem

Maya looks at a pond and says, “That frogspawn can’t be the offspring of the frogs, because it looks nothing like a frog.” Is she right?

⚠ Watch out

Thinking the features themselves get handed over. What is passed from parent to offspring is genetic material (DNA), which holds the instructions for the features.

🧠

Memory hook

Code it, bundle it, hand it on: DNA holds the code, chromosomes are the bundles, and reproduction hands them on.

✓

Check yourself

Without looking back: name the four links in the inheritance chain in order, then say one thing that is different when the organism is a bacterium.

Flashcards

(13)

What is reproduction?

The process of making new living things, called offspring. It is one of the common processes of all living organisms.

What is a life cycle?

The stages a living organism goes through in its life. Organisms reproduce at some point in their life cycle.

Put the frog’s life cycle in order.

Frogspawn, tadpoles, froglets, adult frogs, and then frogspawn again.

True or false: offspring look like their parents from the moment they are made.

False. Offspring resemble their parents at some point in the life cycle, and some do not until later.

How are features inherited?

When genetic material (DNA) is passed from parents to their offspring during reproduction.

What is genetic material?

A substance in cells that contains instructions for inherited features and for life processes such as growth and digestion.

What is DNA made of?

A very long chemical molecule made of smaller chemical units called A, T, C and G.

What is the genetic code?

The order of the A, T, C and G units in DNA. It gives the instructions that build inherited features.

Where is DNA stored in animal, plant and fungal cells?

In the nucleus, organised into packages called chromosomes: big bundles of DNA.

What are the four links in the inheritance sequence?

DNA carries the genetic code, the DNA is packaged into chromosomes, the chromosomes are passed to the offspring, and the offspring inherit the features.

How much genetic material does an offspring inherit from each of two parents?

Half from each parent, so it inherits features from both.

Why are siblings similar but not identical?

They have the same parents, but each offspring inherits a different combination of genetic material, so there is variation.

How do bacteria pass on genetic material?

With one parent: the parent copies its DNA, the cell grows, then it divides to form offspring.

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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A frog’s life cycle

Same parents, not identical

Reproduction and inheritance, in your own words

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