18. Variation and Selection Flashcards
What is variation?
differences between individuals of the same species
What is continuous variation?
a range of phenotypes, between two extremes
What are 2 examples of continuous variation?
body length and body mass
What is discontinuous variation?
a limited number of phenotypes with no
intermediates (a particular characteristic can be divided into distinct categories)
What are 3 examples of discontinuous variation?
ABO blood groups, seed shape in peas and seed colour in peas
What is discontinuous variation caused by?
usually ONLY genes
What is continuous variation caused by?
both genes and environment
Difference in what causes continuous and discontinuous variation
discontinuous variation is usually caused by genes only and continuous variation is
caused by both genes and the environment
Investigate discontinuous variation
- give a control strip to each participant, have them write the number 1 on the strip in pencil
- give the PTC test strips to each participant, have them write the number 2 on the PTC strip in pencil
- each participant to place the control strip on their tongue, record its taste
- each participant to place the PTC strip on their tongue and record its taste
- record number of participants that could taste the PTC or not
What is PTC and how could it be useful?
compound that either tastes very bitter or is virtually tasteless, depending on the genetic makeup of the taster
could be useful in testing discontinuous variation
Investigate continuous variation
- create a table to record the body lengths and arm spans of about 20 people
- measure body lengths of all participants, record in your table.
- measure the arm spans of the same people, record in your table
What is a mutation?
genetic change
What does mutation lead to?
mutation is the way in which new alleles are formed
What are two factor that increase the rate of mutation?
ionising radiation (eg gamma rays, X-rays and high energy UV)
some chemicals
What is gene mutation?
a random change in
the base sequence of DNA
What are sources of genetic variation in populations?
mutation
meiosis
random mating
random fertilisation
What is an adaptive feature?
an inherited feature that helps an organism to survive and reproduce in its environment
What are the adaptive features of hydrophytes?
large, thin leaves
most stomata on the upper surface rather than lower surface
little or no waxy cuticle on their leaves (water loss is not a problem)
long leaf stalks with large air spaces (helps them float)
reduced root system (do not need to be anchored in the ground)
aerial flowers to attract flying pollinators
poorly developed xylem tissue (allows transport of water but provides little support)
What are the adaptive features of xerophytes to reduce water loss?
thick waxy cuticle covering the upper epidermis
few stomata/stomata that are sunken into pits surrounded by hair to reduce water loss by transpiration
curled/rolled/folded leaves, which reduce the SA for transpiration
What are the adaptive features of xerophytes to store water?
thick succulent stem
widely spread roots, close to the surface (plant can absorb as much water as possible even when there is limited rainfall) OR very deep roots to reach underground water sources
Explain the process of natural selection.
- There is genetic variation in a population
- Populations produce many offspring, more than can be supported in the habitat where they live
- Competition between individuals for limited resources (eg food, mates or space)
- Struggle for survival: some individuals are more likely to survive than others
- Individuals better adapted to their environment are more likely to survive and reproduce, passing on their alleles to the next generation
- Offspring of better adapted individuals are more likely to then be better adapted to the environment, survive and reproduce successfully than other individuals in the population
Explain the process of selective breeding.
- humans select individuals with
desirable features - humans cross these individuals to produce the
next generation - humans select the offspring showing the desirable features, only letting these reproduce as well
When and why is selective breeding by artificial selection carried out?
carried out over many generations
to improve crop plants and domesticated animals
What is the process of adaptation?
process resulting
from natural selection by which populations become more suited to their environment over
many generations
Describe the development of strains of antibiotic resistant bacteria when treating with antibiotics.
- During infection, bacteria reproduce quickly in body
- As bacteria reproduce, mutations may occur that allow them to become antibiotic resistant
- Resistant bacteria will have an advantage over the non-resistant bacteria, surviving the antibiotic treatment and reproducing, passing on the allele for antibiotic resistance to the next generation
- Soon, the population will only contain bacteria that are antibiotic resistant
Example of natural selection
development of strains of antibiotic resistant bacteria when using antibiotics
Outline the differences between natural and
artificial selection.
Natural selection: reproductive success is driven by naturally occurring processes
Artificial selection: reproductive success depends on the choices of the breeder
Artificial selection reduces variation within a population
Artificial selection may cause negative effects due to inbreeding
What is inbreeding and why may it be bad?
breeding closely related animals
this produces purebred offspring with particular traits
Risk that parents may carry recessive genes for undesirable traits, which may be passed on to their offspring
