Term 3 - D4.1 Natural selection

D4.1.11 Lamarck’s Theory of Evolution (3)

• Name: Lamarckism OR Inheritance of acquired characteristics

• Lamarck believed that living things could change physically during their life time by using or not using certain body parts, and these changes are passed down to their offspring

• This is not true - physical characteristics are not genetic changes; cannot be passed down

• Lamarckism is wrong !

D4.1.1 Darwin’s Theory of Evolution (2)

• Name: Evolution by natural selection

• Organisms are born genetically different. Those with helpful traits tend to have more offspring, and can better pass down their beneficial traits, so population changes and evolves over generations

D4.1.11 Evolution (1)

Evolution: the cumulative change in the heritable characteristics of a population over time (the end result)

D4.1.11 Natural Selection (1)

Natural selection: is the process where organisms with helpful traits are more likely to survive and reproduce (the process)

D4.1.11 Biodiversity (1)

Biodiversity: evolution by natural selection is a major contributor to biodiversity on the Earth

D4.1.11 The process of evolution by natural selection (5)

1. More offspring are produced than can be supported by the environment

2. Offspring have genetic variations/mutations (good, bad, neutral)

3. Some variations are more favourable than others

4. Tose with favourable traits survive and reproduce

5. Population changes over time, leading to evolution

D4.1.11 Natural Selection is a Paradigm Shift (1)

Darwin’s and Wallace’s theory of natural selection is an example of a paradigm shift from Lamarck’s theory of acquired inheritance

D4.1.2 Muation (2)

• Happens in all living things

• Create new alleles/versions of a gene --> makes a gene pool; random event; good/bad/neutral on survival

D4.1.2 Meiosis (2)

• Happens in sexually-reproducing organisms

• Crossing over (prophase 1) and random assortment (metaphase 1)

D4.1.2 Sexual Reproduction (2)

• Happens in sexually-reproducing organisms

• Any unique sperm can combine with any unique egg

D4.1.2 Asexually-Reproducing Organisms (3)

Asexually-reproducing organisms:

• E.g. bacteria, yeast

• Genetic variations only occur through random mutation

• Rate of reproduction is rapid to make up for the lack of genetic variation

D4.1.2 Sexually-Reproducing Organisms (2)

Sexually-reproducing organisms:

• Have a much greater degree of genetic variation

• This is why they don't give birth to too many offspring

D4.1.2 Variation and Natural Selection (2)

Variation and Natural Selection:

• Natural selection can only occur if there is a genetic variation within a population of species

• Variation is the differences in traits within a population

D4.1.2 Genetic Variation (1 + 2 + 2, 1)

Genetic Variation:

• Genetic variation exists in any population of species because:

  • Mutations generate new alleles in a population

  • Meiosis produces gametes with variation because of

    • Crossing over of alleles

    • Independent assortment of homologous chromosomes during metaphase I

  • Sexual reproduction involves the fusion of gametes. Each parent contributes half of their genetic material to generate new combinations of alleles

D4.1.3 Limiting Factors (3)

Limiting factors:

• Definition: resources that restricts the growth of a population within an ecosystem

• Biotic limiting factors: preys, predators, competition (with different species and individuals of the same species), diseases

• Abiotic limiting factors: water, places for shelter, nutrients in soil, atmosphere, climate

D4.1.3 Carrying Capacity (1)

Carrying capacity: the maximum number of individuals that an environment could support without permanently demining/depleting its resources

D4.1.3 Competition (2)

Intra-specific competition: competition between different species

Inter-specific competition: competition between individuals of the same species

D4.1.3 Overproduction of Offspring and Competition (1)

The overproduction of offspring, and competition, promote natural selection, where the better-adapted individuals are more likely to survive and reproduce

D4.1.4 Density-Dependent Factors (2 + 3)

• Definition: Limiting factors that are related to how many organisms are living within the population (usually biotic)

• Examples:

  • Competition for resources - food, water, access to light, shelter

  • Predation

  • Disease/parasites

D4.1.4 Density-Independent Factors (4)

• Density independent factors limit population growth but are not dependent on population density

• Density independent factors are usually abiotic

• Density intendent factors, such as high or low temperature, may affect the survival of individuals in an ecosystem

• The individuals which are best adapted to the abiotic factors in an ecosystem ae more likely to survive and reproduce

D.1.4 Selection Pressures (1)

Selection pressures cause a particular phenotype to be more favorable in certain environmental conditions

D4.1.5 Survival of the Fittest (3)

• Organisms with phenotypes that makes them better adapted to their environment

• Greater fitness --> higher chance of survival and more likely to reproduce --> greater contribution to the gene pool of the next generation

D4.1.5 Natural Selection (4)

Natural Selection:

• Natural selection occurs because of intraspecific competition for resources

• Individuals that are better adapted tend to survive and produce more offspring, while the less well-adapted tend to die or produce fewer offspring

• Individuals with beneficial genotypes (and phenotypes) are more likely to survive and reproduce than other members of a population

• Natural selection increases the frequency of genes and alleles (genotypes) that make individuals better adapted to the environment and decreases the frequency of other genes and alleles, leading to changes within the species

D4.1.6 Heritable Traits (4)

Heritable Traits:

• Heritable traits encoded in the nucleotide base sequence of genes in organisms are required for natural selection

• Organisms with favourable genes which increase their chances of surviving to reproduce in an environment, are more likely to pass their genes to the next generation

• Over time the frequency of favorable genes increases in a population, which is evolution by natural selection

• Characteristics acquired during an individual's life due to environmental factors are not encoded in their genes, and are not passed to future generations

D4.1.7 Sexual Selection (2 + 2)

Sexual Selection:

• Definition: the process of identifying and choosing potential mates that are best adapted and likely to produce offspring that are also well-adapted

• Exaggerated traits: specific criteria that a male has to attract a female (e.g. colourful feathers in birds)

  • Advantage: desirable for sexual selection - more likely to attract a female

  • Disadvantage: undesirable for natural selection - decreases chance of survival as they are more easily spotted by predators

D4.1.7 Sexual Selection - Birds of Paradise (4)

Sexual Selection - Birds of Paradise:

• The plumage of raggiana birds of paradise is an example of sexual selection

• The plumage makes them more likely to be seen and killed by predators

• However, it makes them more attractive to females, and the males with more extravagant plumage are more likely to pass their genes to the next generation

• The bright, colourful plumage of the males can be a sign of overall fitness in male birds of paradise

D4.1.8 Evolution of Guppies (3)

Evolution of Guppies:

• Colouration of guppies is an inherited trait

• Predators are more likely to kill colourful guppies

• Female guppies are more likely to mate with colourful male guppies - this is an example of sexual selection

D4.1.8 Endler’s Experiment with Guppies

Endler's Experiment with Guppies:

• Endler set up fish tanks with guppies and predators present

• The bottom of the tanks was covered in either coarse gravel or fine gravel

• The guppies in the tanks evolved a pattern of spots which provided the best camouflage in their tank

• The predator was the selective pressure, and the best camouflaged guppies were more likely to survive and reproduce, passing on the genes for camouflage to their offspring

 

• Endler set up fish tanks with guppies without predator's present

• The bottom of the tanks was covered in either coarse gravel or fine gravel

• The guppies evolved a pattern of spots which made them most visible to females

• The visible male guppies were more likely to reproduce and pass on their genes on to the next generation

• This is an example of sexual selection

 

• Endler repeated a version of his experiments with guppies in the wild

• Endler placed dull-coloured guppies in steams with dangerous predators and in streams without dangerous predators

• The guppies in streams with dangerous predators remained dull coloured

• Guppies in streams without dangerous predators evolved to be colourful due to sexual selection