18. Variation Flashcards
Variation
Differences between individuals of the same species.
Genotypic variation
Differences in genotype between individuals
–> occurs because of different combination of alleles
Phenotypic variation
Differences between the phenotypes of organisms
–> occurs due to different genotypes + different environmental factors
Two types of phenotypic variation
Continuous variation
–> Range of phenotypes between two extremes. (eg. height)
Discontinuous variation
–> A particular characteristic can be divided into distinct categories. (eg. blood groups)
Mutation
Genetic change.
Happens when the sequence of bases is altered.
If a mutation occurs in a gamete –> they can be inherited
(How new alleles are formed)
How do mutations occur?
Naturally through DNA replication errors
–> rate of mutation can increase due to…
- Ionising radiation
- Certain chemicals
Causes of variation
- Mutations
- Meiosis
- Random mating
- Random fertilisation
Adaptive features
An inherited feature that increases the fitness of an organism, and helps it to survive and reproduce in its environment.
Birds - Adaptive features (hawk vs hummingbird)
Beak shaped for diet
Hawk - Hooked + sharp for flesh
Hummingbird - Thin + long for nectar
Hares - Adaptive features (arctic vs american desert)
Both…
- Widely spaced eyes (to see predators because of the wide field of vision)
- Long + mobile ears (hearing is adapted to low sounds + many angles)
- Long strong hind legs + large feet (rapid movement)
Arctic hare - Smaller ears to reduce heat loss + brown fur during summer but white during winter.
American desert hare - larger ears to increase heat loss + brown fur all year round
Hydrophytes
Plants that only grow in or on water (water-lily)
Xerophytes
Plants that need very little water (cactus)
Hydrophytes - Adaptations
- Large, thin leaves + stomata on the upper surface instead of the lower surface (which would be below water)
- Little/no waxy cuticle since water loss isn’t a problem
- Long leaf stalks (with air spaces to help them float)
- Barely any roots since they’re not anchored to the ground
- Aerial flower → flying pollinators
- Xylem allows for water transport (but has no structural support as the stem doesn’t need to hold the flower upright/instead the flower floats on water).
Xerophytes - Adaptations
- Thick waxy cuticle limiting water loss
- Few stomata/ stomata in sunken pits surrounded by hair → reducing water loss
- Leaves are curled or rolled → Reduces surface area available for transpiration (through stomata)
- Thick stem (for water storage)
- Widespread root system close to soil surface (for better water absorption)
- Long tap roots (to absorb water from underground aquifers)
- Leaves = sharp spines / needles (deter herbivores + limit water loss)
Natural selection - Stages
1) Overproduction of species
2) Genetic variation
3) Selective pressure (only some survive)
4) Survival of the fittest (adaptive feature)
5) Increase in alleles in population
Natural selection of bacteria - Stages
1) Bacteria asexually reproduce thorugh binary fission
2) Some bacteria mutate to become antibiotic-resistant
3) Antibiotics are used
4) Only antibiotic resistant bacteria survive.
5) The resistant bacteria are able to multiply and increase.
