Natural Selection

Question 1

‘What causes variation

Answer 1

1. Random assortment of chromosomes during meiosis
2. Crossing over
3. Non disjunction
4. Random fertilization
5. Mutations

Question 2

Random assortment

Answer 2

During the formation of the gametes, homologous chromosomes split independent of one another.

Question 3

Crossing over

Answer 3

Crossing over of chromatids during meiosis, may result in pieces of chromatid breaking off and reattaching to a different chromatid resulting a new combination of alleles. This is called recombination.

Question 4

Non disjunction

Answer 4

The failure of chromosomes to separate completely during meiotic divisions is called non disjunction.

Question 5

Random fertilization

Answer 5

When the gametes (sperm and ovum) meet it is also a random match.

Question 6

Mutations

Answer 6

Permanent change to DNA and may result in new chromatids of an individual. It is considered to most important source of variation.

Question 7

Evolution

Answer 7

A scientific theory that all living things are descended from previously living simple organisms.

Question 8

Observing process of evolution in large populations

Answer 8

1. The individuals make only a small contribution to gene pool
2. Evolution occurs slowly
3. Most changes are adaptive
4. Natural selection is the main driving force

Question 9

Observing process of evolution in small populations

Answer 9

1. Individuals make a relatively large contribution to the gene pool
2. Evolution can occur rapidly
3. Many changes are non adaptive
4. Many changes are due to chance events

Question 10

Changes in the gene pool

Answer 10

1. Natural selection
2. Random genetic drift
3. Isolation and the founder effect
4. Migration
5. Barriers to gene flow
6. Genetic diseases

Question 11

Natural selection idea

Answer 11

“Better adapted individuals in a population are more likely to survive and are therefore biologically fitter than the less well adapted.”

Question 12

Why does natural selection occur

Answer 12

1. More offspring are produced than can survive
2. Significant variation in characteristics (variation in allele frequencies)
3. Struggle to exist
4. The ones most likely to survive and reproduce, in the struggle for existence are those best suited for the environment.
5. Favorable feature would become more frequent in each successive generation

Question 13

Struggle to exist

Answer 13

Selective pressures or competition for limited resources. (Food, water, shelter, reproductive partners.)

Question 14

Natural selection in humans

Answer 14

• Inuits have long bodies/short limbs. Smaller surface area: volume ratio = reduced heat loss
• Africans have short bodies/long limbs. Higher surface area: volume ratio = increased heat loss

Question 15

Genetic drift

Answer 15

Refers to the random non directional change in the allele frequencies of small populations over generations. Often caused by chance events.

Question 16

Genetic drift human examples

Answer 16

The Australian - isolated islands off gulf of Carpentaria. Separation from the mainland - abnormally high population of B allele compared to A allele.

Indigenous Australians on the mainland are the opposite.

Question 17

Random Genetic Drift

Answer 17

• Randomness
• Isolated population
• Small population
• Trait to offer NO survival advantage

Question 18

Isolation

Answer 18

Usually occurs when a small group moves away from it’s homeland to a new area and becomes established.

Question 19

Founder effect

Answer 19

The gene pool of an isolated or founding population will be a random subject of the gene pool of the parent population.

Question 20

Founder effect in summary

Answer 20

1. Small group leaves homeland
2. New community does not genetically represent homeland population
3. Migrates to a new region
4. Individuals have high frequency of allele
5. Restricted gene pool
6. Community expands = increased allele frequency

Question 21

Bottleneck

Answer 21

Anything that creates a severe reduction in population size or prevents individuals from breeding, reducing mating possibilities and can cause a genetic bottleneck.

• Wars, natural disasters or migration
• The allele frequency after the disaster by chance is different from before.

Question 22

Migration

Answer 22

The movement of populations, groups or individuals. New organisms may enter a population by migration from another population

Question 23

Gene flow

Answer 23

If members of a migrated populations mate within the population, they can bring new alleles to local gene pool.

Question 24

Barriers to gene flow

Answer 24

Any factor that acts to reduce or block the flow of genes between two populations - Isolating mechanisms

Question 25

Geographic isolation or barriers

Answer 25

- Mountain range - Glaciers/ice sheets - Ocean or large water body - Island - Any physical barrier

Question 26

Sociocultural barriers

Answer 26

- Religious groups - Endogamy - Language barriers - Economic status - Educational background - Social position

Question 27

Genetic diseases

Answer 27

Result in changes to allele frequencies as some alleles cause serious disease, that persist in populations

Question 28

Speciation process

Answer 28

1. Variation 2. Isolation 3. Selection 4. Speciation

Question 29

Variation

Answer 29

Variation between individuals of a species

Question 30

Isolation

Answer 30

Populations isolated without gene flow

Question 31

Selection

Answer 31

Each population has different selective agents (environmental factor acting on the population)

Question 32

Speciation

Answer 32

Allele frequency changes are so significant that two groups can no longer interbreed. They are now considered 2 different species.