Variation and Evolution

Question 1

What is variation?

Answer 1

The difference between members of the same species.

Question 2

What are the two factors that cause variation?

Answer 2

1. Sexual reproduction
2. Mutations

Question 3

Why does sexual reproduction cause variation?

Answer 3

It involves meiosis and fertilisation.

Question 4

What is the process of meiosis?

Answer 4

Meiosis involves halving the number of chromosomes. Each gamete receives one chromosome from each homologous pair. It is random as to which chromosome ends up in a gamete.

Question 5

How many possible chromosome combinations are possible in a gamete?

Answer 5

There are 2^23 possible combinations.

Question 6

What is meant by the term ‘crossing over’?

Answer 6

• Crossing over occurs in chromosomes before they are distributed to the gametes.
• Crossing over involves short regions of homologous chromosomes breaking off and swapping places during meiosis.
• Therefore, there are almost an infinite number of chromosomes during gamete formation.

Question 7

What is a mutation?

Answer 7

A change in the structure and or number of DNA in a cell.

Question 8

Why do mutations cause variation?

Answer 8

Mutations cause variation because of changes in the genetic material of a cell.

Question 9

How can mutations occur?

Answer 9

Mutations can occur spontaneously or be induced by agents called mutagens.

Question 10

What is a mutagen?

Answer 10

Agents that cause an increase in the rate of mutations.

Question 11

What are some examples of mutagens?

Answer 11

Cigarette smoke, ultraviolet radiation, x-rays, gamma radiation, cosmic rays and radon gas.

Question 12

How can mutagens be corrected?

Answer 12

Mutations can be corrected by the cell’s DNA repair enzymes.

Question 13

How is cancer caused?

Answer 13

Cancer is caused by abnormalities in the genetic material of a cell.

Question 14

What are gene mutations?

Answer 14

Changes in the structure of a single gene.

Question 15

What are gene mutations also called?

Answer 15

Point mutations.

Question 16

How are gene mutations caused?

Answer 16

They occur when there is a change in at least one base in DNA, sometimes changing the amino acid sequence in the resulting protein.

Question 17

(5 points)

What is an example of a condition caused by a gene mutation and explain it?

Answer 17

• Sickle-cell anaemia.
• Results from a change in the haemoglobin gene.
• This change leads to the formation of a deformed haemoglobin protein which collapses in on itself.
• The whole cell takes on a sickle or crescent shape and cannot carry as much oxygen.
• Patients who suffer from sickle cell anaemia need regular blood transfusions.

Question 18

What are chromosome mutations?

Answer 18

Changes in the structure of chromosomes or the number of chromosomes. E.g. a chromosome could break in two, become shorter or longer, or even increase in number.

Question 19

(5 points)

What is an example of a condition caused by a chromosome mutation an how is it caused?

Answer 19

• Down’s syndrome.
• Caused by the presence of an extra chromosome 21 in all cells of the individual with DS.
• An error occurs during gamete formation, when a gamete with the two chromosomes 21’s instead of just one.
• When the gamete with two chromosome 21’s joins with a normal gamete at fertilisation, the resulting diploid zygote has three chromosome 21’s.
• This condition is also called trisomy 21.

Question 20

What is evolution?

Answer 20

Genetic changes in a species over a long period of time in response to environmental stress which produces a new species.

Question 21

What is a species?

Answer 21

A group of similar organisms that are capable of interbreeding to produce fertile offspring.

Question 22

What is speciation?

Answer 22

The formation of a new species following many changes in the structure of an organism until the new species cannot interbreed with the original to produce fertile offspring.

Question 23

What are two examples of separate species?

Answer 23

• The cross between a male lion and a female tiger produces a liger. However, ligers are infertile, and therefore a lion and a tiger belong to separate species.
• Similarly a donkey and a horse can interbreed to produce a mule. However mules are infertile. Therefore donkeys and horses are also separate species.

Question 24

What is meant by the term natural selection?

Answer 24

The process by which particular traits become more common in a population due to the trait being advantageous to a species.

Question 25

What does natural selection rely on?

Answer 25

Natural selection relies on heredity, which is the passing on of features from one generation to the next.

Question 26

Who first described natural selection?

Answer 26

Charles Darwin in his publication,*On the Origin of Species.*

Question 27

Who else also came up with the theory of natural selection?

Answer 27

Alfred Russel Wallace.

Question 28

What are two examples of natural selection?

Answer 28

* Sickle-cell anaemia. * MRSA.

Question 29

What observations were made in Darwin's theory of natural selection?

Answer 29

1. Species produce many more offspring than is necessary (overbreeding). 2. There is a limited supply of resources to allow survival of the species. 3. Numbers of species remain relatively constant over long periods of time. 4. All species show variation among the members and these variations are inherited.

Question 30

What conclusions were made in Darwin's theory of natural selection?

Answer 30

1. There is a struggle for existence (competition) between species and between members of the same species for food, space, shelter and mates. 2. Organisms most suited to their environment due to favourable characteristics, will survive and reproduce at a faster rate than those not well suited. 3. The characteristics that make an organism most suited to its environment wil accumulate among the population.

Question 31

Name two pieces of evidence for evolution and Darwin's theory of natural selection.

Answer 31

1. Palaentology 2. Comparative anatomy

Question 32

What is palaeontology and how does it provide evidence for the theory of evolution?

Answer 32

* Palaeontology is the study of fossils. * Palaentology supports the theory of evolution as fossil records show a detailed history of the timeline of evolution and how organisms (including humans) adapted over millions of years. * Palaentologists can dig deeper and deeper into rocks to show how fossils laid down over billions of years change. It has been shown that, over tens of millions of years, the fossilised remains of living organisms have been getting more complex in structure. This shows that life became more and more complex over time.

Question 33

What is a fossil?

Answer 33

The preserved remains of an organism, part of an organism or an imprint left by that organism.

Question 34

What is comparative anatomy and how does it provide evidence for the theory of evolution?

Answer 34

* Comparative anatomy is the study of similarities and differences in the anatomy of living organisms. * The pentadactyl limb is common to many different organisms, such as humans, moles, seals, bats, horses and birds. * Even though the pentadactyl limbs from the differetn organisms can look very different and can have very different functions, they are struturally similar. This means that these organisms must have had a common ancestor many millions of years ago.