Ch. 14 Evolutionary Mechanisms

Question 1

What are 5 processes that cause variation among individuals

Answer 1

random assortment

crossing over

non disjunction

random fertilisation

mutation

Question 2

in terms of evolution what is the most important process of variation amoung individuals

Answer 2

mutation

Question 3

What are the 5 mechanisms for changes in allele frequencies

Answer 3

natural selection 
random genetic drift + founder
migration 
barriers
genetic diseases

Question 4

define natural selection

Answer 4

the process by which a species becomes better adapted to its environment; those individuals w/ favorable characteristics have a survival advantage and so pass those characteristics on to subsequent generations

Question 5

what causes natural selection

Answer 5

variation + selection pressures

Question 6

define random genetic drift

Answer 6

the occurrence of characteristics in a population as a result of chance rather than natural selection; only occurs in small populations

Question 7

what is the difference in random genetic drift and natural selection

Answer 7

1- RGD non directional (chance) and NS directional

2. RGD small populations

Question 8

Define founder effect

Answer 8

A type of genetic drift that occurs when a new population is formed by a small n# of individuals; small sample size cause marked deviations in allele frequencies from the original population

Question 9

describe the process of founder effect

Answer 9

• Small group moves away from homeland to new area + establishes a community, which later expands
• Migrant group= so small # of original population // not genetically representative of them
  o // new community shows features not typical of original homeland population
  o Shows loss genetic diversity as descended from small number of original settlers

Question 10

Define migration

Answer 10

gene flow (transfer of alleles from one population to another through migration) from one population to another

Question 11

example of migration

Answer 11

• When immigrants to a certain country brings alleles that are not already in population, frequencies of that gene will be altered
• E.g. brings disease // decrease in population (occurred in Australia)
  o Remaining pop= genetic resistance

Question 12

what are the four steps of barriers to gene pool

Answer 12

1. Population kept apart by barriers (inhibit interbreeding)
2. No two environments exactly same // environment pressures different
   - = Slightly different characteristics being favored
3. Allele frequencies change over time of each gene pool changes, depends on characteristics favorable for survival
   - Over time= less alike as develop characteristics better suited to respected environments
4. Isolation results in development of separate gene pool

Question 13

what are the two types of barriers

Answer 13

>

Geographical barriers: a feature of the landscape that prevents populations from interbreeding; includes oceans, mountain ranges, large lake systems, deserts, expansive ice sheets
Sociocultural barriers: barriers to interbreeding that are due to social + cultural factors; economic status, educational background, social position, religious affiliation

Question 14

What are alleles causing fatal diseases expected to do

Answer 14

expected to be gradually eliminated from population= people die // do not pass on

Question 15

what occurs to make some fatal alleles remain in population or be high frequency

Answer 15

1. RGD (if small + isolated)
2. ♣ If heterozygous for fatal= increased resistance to another disease // advantage in situations where 2nd disease is prevalent e.g.
   • person with 2 normal alleles= dies,
   • person with 2 fatal alleles= dies,
   • person heterozygous= lives
   • // reproduces + pass allele to generations (survival advantage)

Question 16

define evolution

Answer 16

gradual change of characteristics of a species

Question 17

what were darwins 3 observations

Answer 17

1. Variation
   o members vary
   o passed on
2. Birth rate
   o produced at a rate far greater than food supply= overcrowding
3. Natures balance
   o Although birth rate of organisms ↑ , each species’ numbers= remain constant

Question 18

what were darwin three interpretations

Answer 18

1. Struggle for Existence
   - Excessive birth rate + limited resources
2. Survival of the Fittest
   - Range of variations in species, those with characteristics best suited to their environment were more likely to survive
   -
3. Variation
   > The differences that exist between individuals or populations of a species
   - Members of a species differ from one another in their physical characteristics, body functioning and behavior
   - Many of these features inherited (due to effects of meiosis and fertilization, alleles)

Question 19

Define survival of the fittest

Answer 19

A principal whereby organisms with favorable characteristics survive, while those with unfavorable characteristics die before they had the opportunity to reproduce (and pass on unfavorable characteristics)

Question 20

What are two examples of natural selection in humans

Answer 20

Body stature

Sickle cell anaemia

Question 21

explain the survival advantages of each body stature

Answer 21

Long body + short limbs

• smaller surface area to body volume ratio
• // lose less heat in cold environment
• Cold environments

Short body + long limbs

• Larger surface area to body volume ratio
• // lose more heat in hot environment
• Hot climates

Question 22

What are symptoms of sickle cell anaemia

Answer 22

o	 Clogged blood vessels
o	Pneumonia 
o	Rheumatism 
o	Heart disease
o	Inflammation on hands and feet
o	Anemia

Question 23

what does the mutant allele of sickle cell cause

Answer 23

• = responsible for sickle cell shape
  o Causes substitution of one amino acid (valine) for another (glutamic acid) during formation of hemoglobin
  o Affect functioning of RBC
  ♣ Called Hemoglobin S
  ♣ Cells contain it collapse into sickle shapes at low oxygen

Question 24

explain selective agent

Answer 24

any factor that causes the death of organisms with certain characteristics but which has no effect on individuals without those characteristics

Question 25

explain malaria as a selective agent

Answer 25

• Observed= SCA only occurs in areas of malaria
  o Those heterozygous with SCA= more resistant to malaria // survival advantage in areas where malaria is present
• SCA= natural selection in human population
  o Favorable mutation established new allele in population
  o Having one of these alleles= survival advantage in certain areas (malaria present)
  ♣ Homozygous SCA= dies of SCA
  ♣ Homozygous normal= dies of malaria (more susceptible)
  o // Presence of malaria acted as selective agent for SCA

Question 26

define speciation

Answer 26

The process of a new species developing

Question 27

what are the 4 steps of speciation

Answer 27

1. Variation: Range of variations exists within a population, which shares a common gene pool
2. Isolation: a barrier has formed, dividing population. No interbreeding occurs b/w the two populations // each population has a separate gene pool
3. Selection: Different selection pressures act on each of the two populations over a number of generations. Brings about change in gene frequencies of each gene pool= two subspecies begin to form
4. Speciation: over time changes to gene frequencies great enough to prevent production of fertile offspring by interbreeding between two populations from occurring again. Two species now exist