Variation and natural selection Flashcards
Variation
differences between individuals of the same species
Phenotypic variation and genetic variation
- The two types of variation is Phenotypic variation and genetic variation.
- Genetic variation: Each organism in a species has a different set of DNA, due to genetic variation. Genetic variation is increased during meiosis, which produces gametes. Each gamete produced has different set of alleles, thus when two gametes fuse, new set of genes are produced
- Phenotypic variation: Ex:Hair and height. Phenotypic variation is caused by both genetic and environmental factors.
Continuos variation
continuous variation results in a range of phenotypes between two extremes, e.g. height in humans
Discontinuous variation
discontinuous variation results in a limited number of phenotypes with no intermediates, e.g. tongue rolling, mainly caused by genes alone.
Mutation
genetic change, which result in changes in sequence in DNA bases. The changes occur due to exposure to some chemicals and ionizing radiation. If mutation occurs at particular allle, this allele may be altered changing how it functions, in which new alleles are formed
Gene mutation
A change in the base sequence of DNA
Sickle-cell anaemia
Condition where RBC become sickle shaped. Sickle cells carry less oxygen and can block blood vessels. Caused by a mutation in beta-haemoglobin gene, which alters the allele which produces haemoglobin (protein), It is recessive. Thus, only present in the phenotypesif two copies of this allle is present (homozygous). However, people who are homozygous and heterozygous, have one-sickle cells allele and one un-mutated allele, are immune to malaria. As malaria cannot finfect sickle shaped cells. Sickle cell anaemia is found in places where malaria is common. Thus natural selection of this gene occur in these areas, as those with the green do not catch diseases and are more likely to survive, allows allele to be preserved.
Adaptive feature
The inherited functional features of an organism that increase its fitness
Fitness
Probability of an organism surviving and reproducing in the environment in which it is found
Adaptive features of xerophytes to their environments
Xerophytes are plants adapted to live in very dry climates (cacti), have adaptive features that help increase survival by reducing water loss.
- Fewer stomata: Water vapour diffuses out plant via stomata, thus less water is lost if there are fewer stomata, they also sunken in pits in leaf, allows bubbles of moist air to be trapped around them. It lowers the water potential gradient, less water is removed from the leaf.
- Small, rolled leaves or spines: Reduces surface area of leaves and traps moisture to lower the water potential gradient, reducing water loss.
- Deep roots: Allows plants to absorb water from soil, roots also adapted to absorb large amounts of water when it rains for storing, monsoon season.
- Thick waxy cuticle: Provides waterproof barrier around leaf to prevent waterless.
Adaptive features of hydrophytes to their environments
Adapted in very wet conditions, Water lily, lotus. They do not minimize water loss.
- Leaf shape: Usually large and flat to have large surface area which promotes waterless.
- Stomata: Positioned on the top of the leaf, where sun hits. Large number of stomata present, open to allow water vapour to diffuse out the leaf.
- Thin/No waxy cuticle: water loss does not need to be restricted by this layer in hydrophytes.
- Small root system: large amounts of water reliably available, root systems can be shallow and water can diffuse directly into the system.
Natural Selection
Where organism with favorable allele and advantageous characteristics have a higher probability of serving and reproducing. Due to competition, within a population for resources and mates. As there is variation, in alleles of species, each organism has different traits, some positive some negative. Those with more positive traits can adopt to the environment more effectively. Thus more likely to survive and produce many offsprings. which inherit those ales. Over time, Negative characteristics are lost from the species of an organism, which those characteristics which are not able to reproduce to pass on their allele. Known as evolution. Evolution allows a population to become more adapted to the environment overtime as a result of natural selection.
Adaptation
The process, resulting from natural selection, by which populations become more suited to their environment over many generations.
Development of strains of antibiotic resistant bacteria as an example of evolution by natural selection
Some Bacterial strains become resistant to antibiotics as a result of natural selection.
- Mutation occurs in bacterial cell, which makes it resistant to antibiotic.
- When antibiotic is administered, the cell is not killed, whereas cells which have not become resistant are killed.
- The resistant cell therefore survive and reproduce, passing on the restart allele to produce more resistant bacteria.
Selective breeding:
Where humans select animals of plants with desirable features and breed them together to produce and offspring with these desirable features. Process is repeated over many generations. As breeding is controlled by humans, is is artificial selection.
