Variation and Natural Selection

Question 1

Variation

Answer 1

Variation: The differences in the phenotype of a species.

There are two types of variation: Continuous and Discontinuous.

Question 2

Continuous Variation

Answer 2

-Range of values.
-Caused by genetics and environmental factors.
-For example, height and weight.
-Displayed on a Histogram (no spaces between bars).

Question 3

Discontinuous Variation

Answer 3

-Set values.
-Caused by genetics only.
-For example, blood group and tongue rolling.
-Displayed on a Bar Chart (spaces between bars).

Question 4

Causes of Genetic Variation

Answer 4

-Meiosis (genetic crossover and independent assortment)
-Mutation
-Sexual reproduction (random nature)

Question 5

Environmental Variation

Answer 5

The actual height a human grows to depends on their quality of nutrition.

Question 6

Natural Selection

Answer 6

-There is variation in the phenotypes of a population;
-there is struggle for existence and therefore competition for resources, which leads to the better adapted organism surviving (state adaption and give reason);
-those with the xxxxx gene reproduce, passing on the gene to their offspring;
-over many generations, the population of the offspring with the xxxxx gene will increase.

Question 7

Definitions

Answer 7

Species: An organism that is capable of interbreeding and producing fertile offspring.

Evolution: A continuous process in which there is a gradual change in a species over time in response to changes in the environment.

Endangered: When the population of a species is so low it is at risk of becoming extinct.

Extinction: When there are no living examples of a species left.

What are the causes of Extinction?
-Climate change/ natural disasters
-Hunting by humans and animals
-Spread of disease

How can we reduce Extinction?
-Visit nature reserves.
-Promote legislation that prevents hunting endangered species.

Question 8

Fossils

Answer 8

Fossils are remains of living organisms that have been preserved (in rocks) for millions of years.

How do Fossils provide evidence for evolution?

They show what a plant/ animal looked like millions of years ago and they show how a plant or animal has changed over time.

Question 9

Selective Breeding/ Artificial Selection

Answer 9

Selective Breeding involves Human Intervention.

-Farmers/ humans select an advantageous trait;
-they breed two organisms with this trait (cross pollination in plants);
-over many generations, all offspring will display the desired trait.

Examples of advantageous traits

Wheat: Large grain size and short stalk.
Cows: High milk yield, high beef yield.
Vegetables/ Fruit p: Large yield, disease resistant, frost resistant.

Evaluation of Selective Breeding

Advantage: Maintains the desirable characteristics.
Disadvantage: No variation could result in all the population being susceptible to a particular disease.