Ch. 14 Evolutionary Mechanisms Flashcards
What are 5 processes that cause variation among individuals
random assortment
crossing over
non disjunction
random fertilisation
mutation
in terms of evolution what is the most important process of variation amoung individuals
mutation
What are the 5 mechanisms for changes in allele frequencies
natural selection random genetic drift + founder migration barriers genetic diseases
define natural selection
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
what causes natural selection
variation + selection pressures
define random genetic drift
the occurrence of characteristics in a population as a result of chance rather than natural selection; only occurs in small populations
what is the difference in random genetic drift and natural selection
1- RGD non directional (chance) and NS directional
- RGD small populations
Define founder effect
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
describe the process of founder effect
- 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
Define migration
gene flow (transfer of alleles from one population to another through migration) from one population to another
example of migration
- 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
what are the four steps of barriers to gene pool
- Population kept apart by barriers (inhibit interbreeding)
- No two environments exactly same // environment pressures different
- = Slightly different characteristics being favored - 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 - Isolation results in development of separate gene pool
what are the two types of barriers
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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
What are alleles causing fatal diseases expected to do
expected to be gradually eliminated from population= people die // do not pass on
what occurs to make some fatal alleles remain in population or be high frequency
- RGD (if small + isolated)
- ♣ 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)
define evolution
gradual change of characteristics of a species
what were darwins 3 observations
- Variation
o members vary
o passed on - Birth rate
o produced at a rate far greater than food supply= overcrowding - Natures balance
o Although birth rate of organisms ↑ , each species’ numbers= remain constant
what were darwin three interpretations
- Struggle for Existence
- Excessive birth rate + limited resources - Survival of the Fittest
- Range of variations in species, those with characteristics best suited to their environment were more likely to survive
- - 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)
Define survival of the fittest
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)
What are two examples of natural selection in humans
Body stature
Sickle cell anaemia
explain the survival advantages of each body stature
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
What are symptoms of sickle cell anaemia
o Clogged blood vessels o Pneumonia o Rheumatism o Heart disease o Inflammation on hands and feet o Anemia
what does the mutant allele of sickle cell cause
- = 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
explain selective agent
any factor that causes the death of organisms with certain characteristics but which has no effect on individuals without those characteristics
explain malaria as a selective agent
- 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
define speciation
The process of a new species developing
what are the 4 steps of speciation
- Variation: Range of variations exists within a population, which shares a common gene pool
- Isolation: a barrier has formed, dividing population. No interbreeding occurs b/w the two populations // each population has a separate gene pool
- 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
- 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
