Ch18 Variation And Mutations

Question 1

DEFINE variation

Answer 1

The difference between individuals of the same species

Question 2

What causes variation?

Answer 2

1. Sexual Reproduction: Independent assortment of chromosomes during meiosis ensures great genetic variation. There is random fertilisation so any gamete from each parent can fuse, so no 2 siblings are identical.
2. Mutation: mutations are random and often not expressed in phenotypes.

Question 3

DEFINE mutation

Answer 3

A change in the amount of structure of the DNA. Can be random and occur anywhere on the chromosome.

Question 4

What causes mutation?

Answer 4

1. Mutagens
2. Faulty DNA replication

Question 5

DEFINE mutagen

Answer 5

Outside agents that cause mutations. Eg, ionising radiation, chemicals like cigarette smoke

Question 6

State the 2 types of mutation.

Answer 6

1. Gene/point mutation
2. Chromosome mutation

Question 7

DEFINE gene mutation.

Answer 7

Changes in a single gene, Eg sickle cell anaemia.
Happens due to change in a single base pair.

Question 8

DEFINE chromosome mutation

Answer 8

Large changes in the number or structure of chromosomes. Eg, Downs Syndrome.

Question 9

What chromosome mutation causes Downs Syndrome?

Answer 9

An extra chromosome (Trisomy 21)

Question 10

DEFINE evolution

Answer 10

The way in which organisms change genetically over a long period of time or due to environmental changes.

Question 11

Who discovered evolution?

Answer 11

Darwin and Wallace

Question 12

What is Darwin’s theory?

Answer 12

The Theory of Natural Selection

Question 13

Describe Darwin’s theory.

Answer 13

1. Variation occurs due to competition. Survival depends on adaptations such as producing more offspring and passing on desirable traits to make them more suited to their environment.
2. Despite high birth rates, population of species stays generally constant. This is due to high death rates in baby offspring as a result of high competition for limited resources.
3. Only the genetically best adapted individuals will survive. Their stronger genes will be passed to the next generation.
4. Mutations can lead to new phenotypes which in turn make better adaptations. Traits that give advantage are passed to offspring, so only the strongest survive. This is ‘survival of the fittest’.

Question 14

Why do species populations remain generally constant?

Answer 14

There are high death rates in baby offspring due to high competition for limited resources. Only the strongest and best adapted will survive.

Question 15

What is meant by survival of the fittest?

Answer 15

Only organisms that are genetically best adapted and pass advantageous traits to offspring will survive.
Only the strongest and best adapted organisms will survive.

Question 16

Give an example of evidence for evolution.

Answer 16

1. Study of fossils.
   Fossils can be carbon dated and allow us to construct a time scale of a particular species. Fossils discovered to date show variations and changes to modern organisms.
2. Comparative Anatomy.
   The study of structural similarities between species of the same broad grouping.

The front limbs of many vertebrates (humans, birds, dolphins, etc) have different looking limbs that are adapted for different functions. However, each limb is based off the same basic pattern of bones forming the five-toed forelimb. This indicates that all vertebrates evolved from a common ancestor.