Topic 2: Evoluation And Speciation

Question 1

EVOLUTION

• The significant change in characteristics of a species of an organism
• Characteristics are determined by genes and differences in characteristics are caused by alleles (variation in genes)
• Evolution occurs when there has been a significant shift in the frequency of an allele in a population
• Evolution can be caused by
• Natural Selection
• Genetic Drift

Answer 1

NATURAL SELECTION

• Our current ideas about mechanism of evolution are based on Darwin’s theory
• This is often referred to as survival of the fittest or natural selection
• This means those organisms that survive all competition and produce the most offsprings
• Evolution by natural selection can be explained by variation, competition and reproduction (VCR)

Question 2

VARIATION

• Individual organisms within a population vary considerably in characteristics
• Most variation is due to genetic differences (alleles)
• Variation is important as it allows populations to survive changes in the environment
• Large populations tend to have larger gene pools and therefore show greater genetic variation. This allows them to be more stable
• Species with low genetic diversity are at risk of extinction
• Gene pool: the sum of all the genes in a population

Answer 2

• Mutation: the source of all new genes and therefore new alleles.
• Mutations can be;
• Lethal
• Detrimental
• Neutral
• Beneficial
• Crossing over of homologous chromosomes during meiosis
• Random assortment of chromosomes during meiosis (making of material and paternal chromosomes)
• Random fusion of gametes during fertilisation

Question 3

COMPETITION

• Organisms within a population complete for the same limited resources (abiotic and biotic factors)
• Many more offsprings are produced than are needed to maintain the population size
• There is a struggle for reproduction and survival
• The factors that lead to some organisms living and some dying can be biotic or abiotic
• These factors are called selective pressures
• Some die, those 5hat are best suited to their environment survive

Answer 3

REPRODUCTION

• Organisms possessing certain characteristics will have a greater chance of survival and reproduction
• Evolution occurs when the gene pool changes significantly or when there has been significant shift in the frequency of an allele in a population.

A single organism does not develop an adaptation to a selective pressure, Adaptations develop overtime

Question 4

GENETIC DRIFT

• A mechanism of evolution in which allele frequencies of a population change over generations due to random change, not natural selection
• Occurs in all populations of all sizes, but it’s effects are strongest in all populations
• Beneficial and detrimental alleles have no impact on genetic drift

Answer 4

BOTTLE NECK EFFECT

• Natural disaster occurs and large amounts of a population die
• The killing and survival of animals is random and not caused by natural selection
• The new population will have a significantly different allele frequency and has therefore evolved

Question 5

FOUNDER EFFECT

• A small group of individuals break away from the major population and colonise a new area
• The new population will have a very different allele frequency

Answer 5

SPECIATION

• Organisms are said to be members of the same species if they;
• Have similar morphology
• Have similar DNS
• Have similar amino acid sequence in particular proteins
• Can mate to produce fertile offsprings

Question 6

BIOCHEMISTRY

• more closely related organisms will share similar DNS as they have all evolved together
• This also means that their amino acids sequences will be similar as well

Answer 6

MOrPHOLOGY

• DNA codes for proteins and proteins allow for structure and function
• So it follows that organisms of the same species, which have similar DNA will have similar morphology

Question 7

SPECIATION

• The following are all necessary and in the set order for new species to form from one species;
  1. Two parts of a population become separated by some geographical barrier
  2. Interbreeding between two groups stop
  3. The gene pool will seperate and there is little or no gene flow between them
  4. If the two environments differ, then selective pressures will be different for each group
  5. After many generations of natural selection the two populations can become quite different
  6. The two populations will not be capable of inter-breeding should they mix again
• They show reproductive isolation are new considered seperate species and will be named accordingly.

Answer 7

REPRODUCTIVE ISOLATION

• Caused by reproductive barriers
• Prevents gene flow between species (prevents breeding to produce fertile offsprings)
• Barriers could be pre-zygotic or post-zygotic

Question 8

PRE-ZYGOTIC

• Temporal; Some closely related plant species release pollen at different times of the year
• Mechanical; genitals physically wont fit together
• Behavioural; Some birds perform dances which only attract females from their own species
• Gamete; mating can occur but sperm and egg can’t fuse

Answer 8

POST-ZYGOTIC

• Hybrid Sterility; Unequal chromosome numbers
• Hybrid Inviability; Zygotes can form but are weak and develop poorly. They usually die before being born

Question 9

DIVERGENT EVOLUTION

• Speciation is an example of divergent evolution
• Divergent evolution is the accumulation of small differences between close populations leading to speciation
• Evidence for divergent evolution can be seen in homologous structures

Answer 9

CONVERGENT EVOLUTION
- The development of similar traits on organisms that are not closely related due to similar selective pressures in similar niches (organisms place in the world)