6.3 The Development of Understanding of Genetics & Evolution

Figure 2 shows two species that are members of the Giraffidae family. 

Figure 2

When people first observed the okapi (Okapia johnstoni) in the wild they thought that they were closely related to zebras, but that has since been disproved and they are now known to be a type of giraffe. 

Explain why this change in understanding has occurred. 

The okapi body structure is very similar to how the Giraffa species were before they evolved their long neck. 

In the 1800s, Darwin and Lamarck had different theories about how the short neck of the early species of Giraffa evolved into the long neck of the modern day Giraffa species. 

Use Darwin’s theory of natural selection to explain how the Giraffa's neck evolved.

Lamarck’s theory is different from Darwin’s theory.

Use Lamarck’s theory to explain how the Giraffa's neck evolved.

Suggest why the okapi never evolved a long neck like its Giraffa relatives did. 

In 1866, Gregor Mendel published the results of his investigations into inheritance in garden pea plants.

Figure 3 below shows the results Mendel obtained in one investigation with yellow-seed and green-seed pea plants.

Figure 3

There was a total of 8003 plants in the F₂ generation.

Mendel thought that the production of a large number of offspring plants improved the investigation.

Explain why.

Some of the plants in the diagram are homozygous for seed colour and some are heterozygous.

Complete the table to show whether each of the plants is homozygous or heterozygous. For each plant, tick (✓) one box.

Draw a genetic diagram to show how self-pollination of the F₁ yellow-seed plants produced mainly yellow-seed offspring in the F₂ generation together with some green-seed offspring.

Use the following symbols:

Y = allele for yellow seed colour
y = allele for green seed colour

Using your answer to part (c) and Figure 3, describe whether Mendel's breeding experiments produced the expected ratio of phenotypes in the F₂ offspring. 

Figure 4 shows when four different equine species existed. 

Figure 4

Determine the number of years both Hypohippus and Merychippus existed together.

Using Figure 4, state when the Equus first evolved. 

By viewing the fossil record of these species scientists can get a better understanding of the way that the modern day horse evolved. 

Information about extinct animals is often not clear because the fossil record is incomplete.

Give three reasons why the fossil record is not clear for older species.

Horse evolution is well documented in the fossil record. 

There are many species where gaps in the fossil record make it difficult to understand how they evolved. 

For example, it is difficult to trace the evolution of soft bodied invertebrates using the fossil record. 

Describe how soft bodied invertebrates can be fossilised and explain why we know a lot less about the evolution of soft bodied invertebrates compared to the evolution of horses. 

Fossils are vitally important for providing us with evidence of how different organisms have changed over time.

Figure 1 shows a representation of fossil records indicating how a prehistoric aquatic limbed animal (Ichthyostega) may have evolved from an earlier finned ancestor (Eusthenopteron).

Figure 1

From studying fossils, scientists believe that life on Earth began around 3 billion years ago.

Our understanding of the earliest forms of life however is lacking as the fossil record is incomplete.

Explain why.

When Mount Vesuvius erupted in Italy in 79 AD, many people died in the settlements surrounding the volcano as a result of the release of molten rock and hot ash.

Many victims of the eruption were well preserved and body forms have been excavated by archaeologists.

Explain how and why humans were so well preserved after the eruption of Mount Vesuvius in 79 AD. 

Figure 2 below shows a drawing of a modern giraffe, and its only living relative in the family Giraffidae, the Okapi. 

Figure 2

The Okapi is sometimes referred to as a ‘living fossil’ as it has remained unchanged as a species over a long period of geographical time, and resembles closely the ancestor species that both giraffe and okapi have evolved from.

Both giraffes and okapi are herbivores and consume leaves from shrubs and trees.

Use Darwin’s theory of evolution by natural selection to explain how the giraffe’s long neck evolved.

Outline some of the main events that occurred in the late 19th and early-to-mid 20th Century that gave evidence in support of Mendel’s work.

Figure 3 shows a photograph of the Grand Canyon in Yellowstone National Park, USA.

The canyon formed over many millions of years from the erosion and weathering of rock by the Yellowstone river.

Figure 3

Archaeologists found fossils of five different species of animal, A, B, C, D and E at the locations shown in Figure 3.

All five species are now extinct.

Give two reasons why animals become extinct.

Explain why animals E and C in Figure 3 were not alive at the same time.

Give one piece of evidence that scientists could have gathered from the fossils of animal D to suggest that it evolved from animal B.

The fossils of animals B to E in Figure 3 support Darwin’s theory of evolution by natural selection.

Explain how.