Chapter 17- Selection and Evolution

Question 1

State 4 ways genetic variation is caused

Answer 1

• Independent assortment
• Crossing over
• Random fusion of gametes & random mating
• mutation

Question 2

The phenotype of an organism is a result of interaction between______ and _____________

Answer 2

Genetics!!!
environment!!!

Question 3

Describe Discontinuous variation

Answer 3

• Differences between individuals of a species in which each one belongs to one of a small number of distinct categories with no intermediates
• The environment has no effect on the variation
• different alleles at a single gene locus have large effects on the phenotype
• an example is blood groups; A, B, AB, or O

Question 4

Describe continuous variation

Answer 4

• Differences between individuals of a species in which each one can lie at any point in the range between the highest and lowest values. Is regulated by multiple genes and environment
• different alleles at a single locus have small effects on the phenotype
• different genes have the same, often additive, effect on the phenotype
• A large number of genes may have a combined effect on a particular phenotypic trait; these genes are known as polygenes

Question 5

describe biotic factors

Answer 5

these are environmental factors that are caused by living organisms e.g
- predation
- competition
- diseases

Question 6

describe abiotic factors

Answer 6

environmental factors that are caused by non-living components e.g
- soil
- pH
- light intensity

Question 7

define fitness

Answer 7

• the ability of an organism to survive and reproduce

Question 8

define natural selection

Answer 8

• The process by which individuals with a particular set of alleles are more likely to survive and reproduce than those with other alleles, eventually the advantageous alleles become more frequent in the popuation.

Question 9

define selection pressure

Answer 9

• an environmental factor that affects the chance of survival of an organism whereby an organism with a particular phenotype is more likely to survive than those with a different phenotype

Question 10

describe stabilizing selection and its curve

Answer 10

• this is natural selection that tends to keep allele frequencies relatively constant over many generations
• the selection is against both extremes and fitness is towards the average. Normal bell curve with higher average number

Question 11

describe directional selection and its graph

Answer 11

• natural selection that causes a gradual change in allele frequency over many generations
• the extreme trait is favoured over the others making the graph shift causing the organisms to be more fit.

Question 12

describe disruptive selection and its graph

Answer 12

• This occurs when conditions favor both extremes of a population
• individuals at the extremes of the curve have higher fitness than the average individuals making the curve M-shaped.

Question 13

what can cause directional selection

Answer 13

• selection pressures
• new alleles arise by mutation

Question 14

describe antibiotic resistance as an example of directional selection

Answer 14

• when someone takes antibiotic penicillin to treat an infection, bacteria that are sensitive will die.
• however by chance there may be one or two among the population that have an allele that is resistant to the penicillin, this allele can arise by mutation.
• these bacteria will reproduce rapidly in ideal conditions

Question 15

define genetic drift

Answer 15

• the gradual change in allele frequencies in a small population where some alleles are favoured or lost by chance and not natural selection

Question 16

define gene pool

Answer 16

The complete set of genetic information in a population.

Question 17

This process occurs in a recently isolated small population and results from only part of the gene pool being present in this small population is called ________ ______

Answer 17

FOUNDER EFFECT

Question 18

What is an evolutionary bottleneck

Answer 18

• a period when the numbers of a species fall to a very low level, resulting in the loss of a large number of alleles and therefore a reduction in the species’ gene pool.

Question 19

What does the Hardy-weinberg principle show

Answer 19

• calculation of allele frequencies
• predict how these might change in future generations

Question 20

which alleles do p, p^2 and q, q^2 represent in the equations

Answer 20

p: dominant allele
p^2: Dominant homozygous allele
q: Recessive allele
q^2: recessive homozygous allele

Question 21

The Hardy Weinburg principle cannot apply where:

Answer 21

• The population is too small
• Significant selective pressure against one of the genotypes
• migration of individuals that are carrying one/two alleles out of the population
• non-random mating

Question 22

define artificial selection / selective breeding

Answer 22

The selection by humans of organisms with desirable traits to survive and reproduce

Question 23

outline the steps of selective breeding

Answer 23

1- The population that is chosen has to show variation e.g some individuals being resistant to disease.
2- the breeder selects an individual that has the feature that can last over future generations
3- another parent will be selected showing the same variety or perhaps a different variety that can show another beneficial characteristic. The 2 chosen parents are then bred together
4. once the offspring have grown she will select the ones that show the best combination of these 2 characteristics

Question 24

Define evolution

Answer 24

• A process leading to the formation of new species from pre-existing species over time

Question 25

Define species

Answer 25

• A group of organisms with the same morphological, physiological, biochemical and behavioural features, which can interbreed to produce fertile offspring and are reproductively isolated from other pieces.

Question 26

What are morphological features

Answer 26

These are structural features

Question 27

What are physiological features

Answer 27

• These are features relating to metabolic and other processes in a living organism

Question 28

what are the problems of trying to interbreed two organisms to produce a fertile offspring

Answer 28

• Both of the same sex
• There is no time or enough facilities to interbreed them
• they cannot breed in captivity
• Organisms that produce asexually and not sexually
• Immature and are not able to breed.

Question 29

What are the features that determine whether organisms belong to the same species

Answer 29

• Can breed but offspring is infertile
• Genetic isolation
• DNA sequences
• Morphological features

Question 30

What are the reasons for an inability to interbreed successfully

Answer 30

• individuals do not recognize each other as potential mates
• Animals being physically unable to mate
• incompatibility of pollen and stigma in plants
• failure of cell division in the zygote
• Offspring that soon die
• Viable but sterile offspring

Question 31

Define speciation

Answer 31

The production of new species that can no longer interbreed with one another

Question 32

What causes speciation

Answer 32

• Geographical barrier separates the species into 2 groups
• Where the reproductive isolation happens while the species is still living in the same place.

Question 33

Describe Allopatric speciation

Answer 33

• This is the development of new species following geographical isolation
• Examples of geographical barriers are:
• islands
• a water body
• Over time, the morphological, physiological, and behavioural features will become different between the 2 groups. A new species will evolve

Question 34

Describe sympatric speciation

Answer 34

• This is the development of new species without any geographical separation.
• for this to happen, the 2 groups will have to split, with one group experiencing different selection pressures compared to the other group.
• These selection pressures will force that group to adapt with new morphological and physiological features

Question 35

Define ecological separation

Answer 35

• The separation of 2 populations because they live in different environments in the same area and so cannot breed together.

Question 36

Define behavioural separation

Answer 36

• The separation of 2 populations because they have different behaviours which prevent them from breeding together.