Variation

Cystic fibrosis is a genetic disorder.

Cystic fibrosis affects the movement of substances into and out of cells.

Which part of a cell controls the movement of substances into and out of the cell?

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Cystic fibrosis is caused by a recessive allele, b.

What name is given to the allele B ?

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Which term describes the genotype Bb ?

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Two people plan to have a child.

Both people have the genotype Bb.

Complete Figure 1 to show the possible genotypes of the child.

What is the chance that a child of these parents will have cystic fibrosis?

Use Figure 1.

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An embryo can be tested to find out its genotype.

What is the name of the testing process?

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Inherited disorders can be caused by changes in DNA.

What is the name of a change in DNA?

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Inheritance is one cause of variation in a population.

Environmental factors also cause variation in a population.

Suggest one environmental cause of variation in a human population.

Do not refer to inheritance or to changes in DNA in your answer.

Figure 3 shows one species of bird on a bird feeder.

The birds use their beaks to reach nuts inside the bird feeder.

Figure 4 shows the mean beak length of this species of bird in the UK. This species of bird often visits bird feeders.

Determine the rate of change in beak length from 1984 to 2000. Use Figure 4.

Explain the process of evolution that could cause the trend in Figure 4.

Birds of this species:

• live for about 3 years

• produce up to 24 eggs every year.

Explain why evolution is easier to study in this species of bird than in humans.

Birds of this species are found in different parts of the world. Describe evidence that would show two individual birds are the same species.

This question is about DNA and genes.

Which diagram represents a DNA molecule? Tick (✓) one box.

Describe the structure of a DNA molecule.

A gene is a small section of DNA on a chromosome. Complete the sentences.

A gene codes for a particular sequence of. This sequence makes a specific.

What is meant by the term genome?

The complete human genome is now known. Which important scientific advance was made using knowledge of the human genome? Tick (✓) one box.

A student found six different snails of one species in his garden. Figure 7 shows the snails.

All the snails are different. What scientific term describes differences in characteristics between individuals of a species?

A change in DNA has caused snail P to be very different from the other five snails. Suggest why there might be an increasing number of snails similar to snail P in each future generation.

This question is about DNA and genes.

Which diagram represents a DNA molecule? Tick (✓) one box.

Describe the structure of a DNA molecule.

A gene is a small section of DNA on a chromosome. Complete the sentences.

A gene codes for a particular sequence of. This sequence makes a specific.

What is meant by the term genome?

The complete human genome is now known. Which important scientific advance was made using knowledge of the human genome? Tick (✓) one box.

A student found six different snails of one species in his garden. Figure 1 shows the snails.

All the snails are different. What scientific term describes differences in characteristics between individuals of a species?

A change in DNA has caused snail P to be very different from the other five snails. Suggest why there might be an increasing number of snails similar to snail P in each future generation.

A cat breeder noticed that four kittens from one Siamese cat mother had a new blue colour at the tip of their tails.

What has caused the new colour to appear?

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The cat breeder wants to use selective breeding so that all new kittens have blue tail tips.

Describe the process of selective breeding the cat breeder could use.

Suggest one reason why the cat breeder wants to have all new kittens with the blue tail tips.

Siamese cats can suffer from heart defects.

Why might there be more Siamese cats with heart defects amongst the kittens with blue tail tips?

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With each pregnancy, the cat breeder expected that:

• 50% of the kittens would be male

• 50% of the kittens would be female.

The sex chromosomes in cats are inherited in the same way as in humans.

The sex chromosomes are X and Y.

Give the combination of sex chromosomes present in a male cat and in a female cat.

The cat breeder expected 50% male kittens and 50% female kittens.

Complete the Punnett square in Figure 3 to show why.

Figure 3

In the first pregnancy there was one male kitten and three female kittens.

Give the reason why there were not two kittens of each sex.

Animals have adaptations to survive in their environment. These adaptations may be structural, behavioural or functional.

Draw one line from each animal adaptation to the type of adaptation it is.

Animal adaptation Type of adaptation

Plants also have adaptations. There are more than 28 000 known species of orchid plants.

Many orchid plants:

• grow attached to other types of plants

• have brightly coloured flowers

• produce large quantities of pollen

• produce thousands of tiny, light seeds.

Describe how these adaptations help orchid plants to survive and compete.

A rare orchid has been found in the mountains in China. The orchid has pale yellow flowers. DNA analysis of the genome shows that it is an ancestral species. All other present day orchids evolved from this ancestral species millions of years ago.

One present day species has bright purple flowers. Describe how an orchid with bright purple flowers may have evolved from the ancestral species which has pale yellow flowers.

The DNA code determines the sequence of amino acids which are joined together to form a specific protein. Table 3 shows part of the amino acid sequence for the colour pigment protein in five orchid species. The rest of the amino acid sequence is the same for all the species.

ala = alanine gly = glycine isoleu = isoleucine leu = leucine tyr = tyrosine Suggest which orchid species is most closely related to the ancestral species. Give a reason for your answer.

Variation in individual organisms can be caused by:

• genes

• the environment

• a combination of both genes and the environment.

Figure 7 shows variations in a woman.

What is the cause of each variation in Table 5 ?

Tick only one box in each row.

The allele for blue eyes is recessive (b).

The allele for brown eyes is dominant (B).

A woman has blue eyes.

What are the woman’s alleles?

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The woman marries a man with the alleles Bb for eye colour.

What colour eyes does the man have?

Complete the Punnett square diagram in Figure 8 for this man and woman.

Figure 8

What is the probability that a child of this man and woman will have brown eyes?

What is the scientific term used for the child’s eye colour?

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What effect will a mutation have?

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