Chapter 14 - Evolutionary Mechanisms

Question 1

What are the causes of variation?

Answer 1

• random assortment
• crossing over
• non-disjunction
• random fertilisation
• mutations

Question 2

What is random assortment?

Answer 2

Random assortment of chromosome during meiosis results in gametes that have a large number of possible combinations of the chromosomes that originally came from the male and female parent.

Question 3

What is crossing over?

Answer 3

Crossing over of chromatids during meiosis may result in pieces of chromatic being broken off and attaching to a different chromatid. This results in a changed sequence, or recombination, of the alleles along the resulting chromosome

Question 4

What is non-disjunction?

Answer 4

Where one or more members of a chromosome lair fail to separate during meiosis. This results in gametes that have more or less than the correct number of chromosomes. If such gametes are involved in fertilisation, the resulting embryo will have the incorrect number of chromosomes.

Question 5

What is random fertilisation?

Answer 5

Because each person will produce a huge number of different sperm or eggs with respect to the alleles each contain, and because any speed can fertilise any egg, there is an almost infinite number of possible combinations of the alleles in the offspring.

Question 6

What are mutations?

Answer 6

Permanent changes in the DNA of a chromosome and may result in totally new characteristics in an individual. If the mutation occurs in a gamete, it can be passed on from generation to generation.

Question 7

What is natural selection?

Answer 7

A process by which a species becomes better adapted to its environment; those individuals with favourable characteristics have a survival advantage and so pass those characteristics on to subsequent generations.

Question 8

What are geographical barriers to gene flow?

Answer 8

A feature of the landscape that prevents populations from interbreeding.

Question 9

What are some examples of geographical barriers?

Answer 9

• oceans
• mountain ranges
• large lake systems
• deserts
• expansive ice sheets

Question 10

What are sociocultural barriers to gene flow?

Answer 10

Barriers to interbreeding that are due to social and cultural factors.

Question 11

What are some examples of sociocultural barriers?

Answer 11

• religion
• economic status
• educational background
• social status

Question 12

What were Darwin’s 3 observations?

Answer 12

• variation
• birth rate
• nature’s balance

Question 13

Darwin’ observations: Variation

Answer 13

• all members of a species vary
• these variations were passed on from one generation to the next, characteristics being displayed by parents passed on to their children

Question 14

Darwin’ observations: Birth rate

Answer 14

• all living organisms reproduce at a rate far greater than that at which their food supply and other resources increase
• this would normally result in overcrowding

Question 15

Darwin’ observations: Nature’s balance

Answer 15

• although the birth rate of organisms was high, each species’ numbers tended to remain at a relatively constant level.

Question 16

What is speciation?

Answer 16

The process of new species being developed

Question 17

What are the steps of speciation?

Answer 17

• variation
• isolations
• selection
• speciation

Question 18

Speciation: isolation

Answer 18

• a population exists on an island

- a range of variations exists within the population, which shares a common gene pool

Question 19

Speciation: isolation

Answer 19

• the species is divided into two populations
• a barrier has formed, dividing the population into two
• no interbreeding occurs between the two populations
• each population has a separate gene pool

Question 20

Speciation: selection

Answer 20

• two subspecies begin to form
• different selection pressures act on each of the two populations over a number of generations
• this brings about a change in the gene frequencies of each gene pool
• such changes lead to the evolution of seperate subspecies

Question 21

Speciation: speciation

Answer 21

• two species now exist
• over a long period of time the changes in the gene frequencies may be great enough to prevent the production of fertile offspring by interbreeding between the two populations from ever occurring again
• when this happens, two species exist

Question 22

What is an example of natural selection in humans?

Answer 22

Body stature

Question 23

How does evolution by natural selection occur?

Answer 23

1. Variations in a species
2. More offspring than can survive to maturity
3. Excessive birth rate + limited resources = struggle for existence
4. Favourable characteristics, more likely to survive and reproduce = survival of the fittest
5. Favourable characteristics passed on
6. Over time proportion of alleles that produce favourable characteristics increases

Question 24

What is gene flow?

Answer 24

The transfer of alleles from one population to another through migration