AQA A level Bio 4.4 Genetic Diversity and Adaptation

Explain what is meant by genetic diversity (1)

Difference in allele (1)

The spotted owl is a bird. Numbers of spotted owls have decreased over the past 50 years. Explain how this decrease may affect genetic diversity (1)

Reduced gene pool/fewer varied alleles (1)

A geneticist investigated genetic diversity in four different breeds of dog. She compared DNA base sequences of the same genes from a large number of dogs from each breed.

The geneticist calculated the mean genetic diversity for each breed of dog. The value of this mean was between 0 and 1.

• A mean value of 1 show maximum genetic diversity

• A mean value of 0 shows no genetic diversity

Her results are shown in the table.

Miniature terriers were first bred from bull terriers in the 19th century,

Suggest one explanation for the observed difference in genetic diversity between miniature terriers and bull terriers (2)

miniature terrier breeding has included more out-breeding (1)

increased number of different alleles (1)

Some birds feed on animals found in mud in estuaries. The drawing shows the heads of three species of these birds and their prey

Use the information in the drawing to explain how interspecific competition between the birds is reduced (2)

different birds feed on different prey and have differently shaped beaks (1)

less competition for food so more birds can eat and survive (1)

Some birds feed on animals found in mud in estuaries. The drawing shows the heads of three species of these birds and their prey

Explain how competition might have played a part in the evolution of the long curved beak of the curlew (4)

Genetic diversity leads to some birds having an allele mutation, leading to a longer and more curved beak (1)

Birds with a long curved beak were better adapted to feed on ragworms (1)

Birds without the same shaped beak couldn’t eat and died off (1)

Advantageous allele spreads over time to offspring as more birds survive and reproduce (1)

The Amazonian forest today contains a very high diversity of bird species.

• Over the last 2 000 000 years, long periods of dry climate caused this forest to separate into a number of smaller forests.

• Different plant communities developed in each of these smaller forests.

• Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.

(a) Use the information provided to explain how a very high diversity of bird species has developed in the Amazonian forest (5)

No interbreeding/gene pools are separate (1)

Mutation has occurred (1)

different selection pressures (1)

Adapted organisms survive and breed (1)

Change in allele frequency (1)

The Amazonian forest today contains a very high diversity of bird species.

• Over the last 2 000 000 years, long periods of dry climate caused this forest to separate into a number of smaller forests.

• Different plant communities developed in each of these smaller forests.

• Each time the climate became wetter again, the smaller forests grew in size and merged to reform the Amazonian forest.

Speciation is far less frequent in the reformed Amazonian forest. Suggest one reason for this (1)

Similarly/ same environmental factors (1)

Great tits are small birds. The graph shows the relationship between the number of breeding pairs in the population and the mean number of eggs per nest in different years in a wood

Explain the relationship shown by the graph (2)

Intraspecific variation between the birds for amount of food available as more energy is used trying to find food (1)

Therefore less energy for reproduction (1)

Female great tits usually lay between 3 and 14 eggs in a nest. In the same year, the birds do not all lay the same number of eggs. Explain how one factor, other than the number of breeding pairs, could influence the number of eggs laid by a great (1)

Age of birds (1)

Great tits are small birds.

Natural selection influences the number of eggs laid. Explain why great tits that lay fewer than 3 eggs per nest or more than 14 eggs per nest are at a selective disadvantage.(3)

with a higher number of eggs, each egg will receive less food (1)

therefore they are more likely to die (1)

but with less eggs, there is more likely to be predators (1)

therefore unlikely to pass on genes (1)

In an investigation, the tolerance to copper ions of the grass Agrostis tenuis was determined.

Samples were taken of plants growing in waste from a copper mine and from nearby areas just outside the mine. The mean copper tolerance of plants from the mine waste was found to be four times higher than that of plants in the surrounding area.

Explain how natural selection could produce a copper-tolerant population in the minewaste. (4)

Variation is present in the original population due to possible mutations (1)

Copper-tolerant individuals are more likely to survive (1)

these reproduce and pass on beneficial genes to their offspring/next generation (1)

Allele frequency of copper tolerance increases (1)

In an investigation, the tolerance to copper ions of the grass Agrostis tenuis was determined.

Samples were taken of plants growing in waste from a copper mine and from nearby areas just outside the mine. The mean copper tolerance of plants from the mine waste was found to be four times higher than that of plants in the surrounding area.

Copper-tolerant Agrostis tenuis plants flower at a different time from those which are not copper-tolerant. Explain how this might eventually lead to the production of a new species of Agrostis. (4)

Reproductively isolated (1)

different selection pressures for 2 populations (1)

different traits are selected (1)

populations become genetically different and unable to produce fertile offspring (1)

Most human cells contain two copies of each gene. However, there might be up to 15 copies of the gene for amylase (AMY1). Scientists investigated the number of copies of the AMY1 gene in individual people in two populations. One population had a high-starch diet and the other population had a low-starch diet.

Figure 3 shows their results.

Describe what their results show (3)

low starch, fewer copies (1)

Ranges overlap from 2-13 copies. (1)

The range is greater with high starch (1)

Most human cells contain two copies of each gene. However, there might be up to 15 copies of the gene for amylase (AMY1). Scientists investigated the number of copies of the AMY1 gene in individual people in two populations. One population had a high-starch diet and the other population had a low-starch diet.

Multiple copies of the AMY1 gene is an adaptation to a high-starch diet. Use your knowledge of protein synthesis and enzyme action to explain the advantage of this adaptation. (3)

more transcription (1)

more translation (1)

so reaction is faster (1)

The photograph below shows a waxy leaf frog (Phyllomedusa sauvagii). This species of frog is found in hot, dry areas of South America. It has glands that produce waxy lipids to spread over its skin. This reduces water loss. The waxy leaf frog is active only at night, when it hunts for insects in the trees.

Suggest how natural selection could have given rise to the adaptations shown by the waxy leaf frog (5)

idea of selection pressure (1)

rf to competition predation (1)

mutation in frog leads to a advantageous allele (1)

Frogs with the advantageous allele survive better and breed alleles (1)

passing on future generations (1)

In the mountains of North America, when winter changes into spring, the coat
colour of snowshoe hares changes from white to brown. Climatic changes
have caused the snow to melt earlier. This has reduced the survival rate of
snowshoe hares in these habitats. The change in coat colour occurs when
new fur replaces old fur. This is called moulting. Recent research has shown
that snowshoe hares within a population moult at different times. Moulting at
different times could be a major factor in ensuring the survival of snowshoe
hare populations.
Snowshoe hares within a population moult at different times

Explain how this could ensure the survival of snowshoe hare populations in these mountain habitats (4)

Hares who moult earlier are more likely to survive (1)

Hares which moult earlier (more likely to) reproduce (1)

Pass on (advantageous) allele(1)

Frequency of allele increases (in future populations) (1)