Topic 18 (Variation and Selection) Flashcards
What are variations?
*Variations are differences in traits between individuals of the same species.
*Variation can be discontinuous or continuous.
Describe discontinuous variation.
*Controlled by one or few genes
*Have clearly defined differences with few or no
intermediate forms
*Not affected by environmental conditions
Describe continuous variation.
*Brought about by the combined or additive effect
of many genes
*Shows a range of traits with intermediate forms
*Affected by environmental conditions
What are sources of genetic variation?
1.Mutation:
*Genes are usually passed on from one generation to another unchanged.
*Heredity depends on the accuracy of gene copying or replication.
*Mutation is a sudden and random change in the structure of a gene or in the chromosome number.
*Gene mutation is a sudden and random change in the base sequence in the DNA.
*Mutation results in new alleles , and the offspring produced will be genetically different.
*Exposure to mutagenic agents or mutagens such as X rays, ultraviolet light and formaldehyde in cigarette smoke increase the risk of mutation.
What are sources of genetic variation?
2.Meiosis and random fertilisation:
*Random combinations of parental chromosomes that occur during meiosis produce genetically different offspring.
*Random fertilisation then produces even more variations in the offspring.
3.Random mating:
*Random mating between different varieties of the same species will produce greater genetic
variations within the species.
4.Variation and selection:
*Genetic variations may give an organism a selective advantage or disadvantage to survive
in a particular environment.
What are adaptive features?
Organisms develop and inherit features that help them survive and reproduce in a particular environment. These
inherited features are called adaptive features.
What are some examples of adaptive features?
Xerophytes:
*Xerophytes are plants that have adaptive features which
help them survive in arid or desert like conditions.
*Such adaptive features include:
-needle like leaves
-a thick waxy cuticle
-sunken stomata
-hairs
What are some examples of adaptive features?
Hydrophytes:
*Hydrophytes are plants that have adaptive features
which allow them to live in the water or float on the
surface of the water.
*Such adaptive features include:
-absence of cuticle and stomata
-large air chambers in the leaf
-stomata in the upper epidermis
What is natural selection?
*Variations in organisms can produce varieties that are more competitive, more resistant to diseases and better
adapted to changes in the environment to survive and reproduce.
*Other varieties that are susceptible to diseases or environmental changes may die. This process is called
natural selection.
*Over many generations, natural selection can produce several different species from a common ancestor, each
adapted to a particular diet or environment. This process is called adaptive radiation.
How do new species evolve?
*The process involving a series of genetic variations from the original species to the development of a new species is called evolution.
*The process by which organisms develop and inherit adaptive features through natural selection is called
adaptation . Through this process, populations become more suited to their environment over many generations.
How does natural selection lead to the development
of antibiotic resistant bacteria?
Improper or indiscriminate use of antibiotics can lead to drug resistance in bacteria.
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Overexposure or underexposure to antibiotics can cause some strains or varieties of bacteria to develop genetic mutations that help them to survive.
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These mutations will then be passed on to the next generation.
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This leads to the evolution of a new strain of antibiotic
resistant bacteria via natural selection.
What is artificial selection?
*For thousands of years, humans have been trying to produce improved breeds of plants and animals by
selective breeding
*The process of producing plants and animals with desirable traits is called selection
Describe selective breeding of plants.
Selective breeding of plants:
*Soya bean breeders want seeds that have high oil
content.
*Different varieties of plants are crossed to produce a
new and better variety in a process called
hybridisation
*The hybrid produced has the desirable combination
of genes from the two parental varieties.
Describe selective breeding of animals.
Selective breeding of animals:
*Cows that produce more milk are selected and used
as female parents for the next generation.
*Unlike plants, animals cannot be self fertilised
*Cows with desirable traits are mated with a bull with
desirable traits to produce offspring with the
desirable gene combination.
What are the differences between artificial selection and natural selection?
Artificial selection:
Selection is done by humans
Humans select the features for their benefit
Not for survival or evolution
Genetic variation decreases
Usually a faster process
Natural selection:
Selection by environmental conditions
Features selected are for the organisms’ benefit
For survival or evolution
Genetic variation increases
Usually a slower process
