variation and selection Flashcards
variation
the differences between individuals of the same species
continuous variation
results in a range of phenotypes between two extremes
- body length, body mass
discontinuous variation
results in a limited number of phenotypes with no intermediates
- ABO blood groups, seed shape + colour in peas
difference between continuous and discontinuous variation
discontinuous depends on genes only but continuous is caused by both genes and environment
mutation
genetic change
how are new alleles formed
mutation
stuff that increase rate of mutation
- ionising radiation
- some chemicals (mutagens)
gene mutation
change in the base sequence of dna
adaptive feature
an inherited feature that helps an organism to survive and reproduce in its environment
adaptive features of xerophytes
- sunken stomata reduces water vapour loss
- thick leaves and stem to absorb more water
- long roots to reach water in soil
- small leaves to reduce surface area for evapration
adaptive features of hydrophytes
- small roots as they can absorb from tissues as well
- large stomata
- flat broad leaves to float
natural selection
- there is genetic variation among a population
- as many offspring are produced
- there’s a struggle for survival due to competition for resources
- there’s a greater chance of reproduction by individuals that are better adapted
- they pass on their alleles to the next generation
selective breeding
- humans select individuals with desirable features
- they are crossed to produce the next generation
- offspring with desirable features are selected
why selective breeding
to improve crop plants + domesticated animals
adaptation
the process, resulting from natural selection, by which populations become more suited to their environment over many generations
