Ch 18 - (Variation & Selection) Flashcards
Define Variation.
differences between individuals of the same species
What is phenotypic variation?
difference in features between individuals of the same species
How are the differences in phenotypic variation caused?
differences in genes, which is genetic variation
What are the 2 types of phenotypic variations?
1.Continuous Variation
- Discontinuous Variation
What is continuous variation?
- very many small degrees of difference for a particular characteristic between individuals
- they are arranged in order and can usually be measured on a scale
Ex- height, mass, finger
What is discontinuous variation?
distinct differences for a characteristic
How is phenotypic variation caused?
- It can be genetic - controlled entirely by genes
- environmental - caused entirely by the environment in which the organism lives
What are examples of genetic variation in humans?
- blood group
- eye colour
- gender
- ability to roll tongue
- whether ear lobes are free or fixed
What are characteristics of all species affected by?
environmental factors such as climate, diet, accidents, culture and lifestyle
What is discontinuous variation caused by?
genetic variation alone
What are mutations?
genetic changes
What do mutations lead to?
- o effect on the phenotype
- development of new alleles and so new phenotypes and if they do, most have a small effect
- harmful changes (Ex- sickle cell anaemia)
What do alleles give an individual?
survival advantage over other members of the species
How do mutations happen?
spontaneously and continuously
How can the frequency of mutations be increased?
- Ionising radiation (e.g. gamma rays and X - rays) - which can damage bonds and cause changes in base sequences
- non-ionising radiation (e.g. ultra-violet) - can also damage bonds and cause changes in base sequences
- Certain types of chemicals - for example chemicals such as tar in tobacco
What can increased rates of mutations lead to?
cancerous
What re the ways in which genetic variation happens?
- Mutations:
- random genetic changes to the base sequence of DNA
- New alleles form through these random changes to
DNA
- Meiosis
- New allele combinations form through segregation - Random mating
- Which partnerships form for sexual reproduction - Random fertilization
Which sperm and egg combinations occur during sexual reproduction
What are adaptive features?
inherited functional features of an organism that increase its fitness
what is fitness?
probability of an organism surviving and reproducing in the environment in which it is found
What is hydrophytes?
Plants adapted to live in extremely wet conditions
What are common adaptations in hydrophytes?
- Large air spaces in their leaves
- Small roots
- Stomata
What does Large air spaces in their leaves do as an adaptation for hydrophytes?
for flotation, to keep the leaves close to the surface of the water where there is more light for photosynthesis
What does Small roots do as an adaptation for hydrophytes?
extract nutrients from the surrounding water through their tissues
What does stomata do as an adaptation for hydrophytes?
open all the time and mainly found on the upper epidermis of the leaf where they can exchange gases much more easily with the air
What is xerophytes?
Plant adapted to live in extremely dry conditions
What are common adaptations in xerophytes?
- Thick waxy cuticle
- Sunken stomata
- Leaf rolled
- Small leaves:
5.Extensive shallow roots
6.Thickened leaves or stems
What does thick waxy cuticle do as an adaptation for xerophytes?
- the cuticle cuts down water loss in two ways:
- it acts as a barrier to evaporation and also the shiny
- surface reflects heat and so lowers the temperature
What does Sunken stomata do as an adaptation for xerophytes?
- stomata may be sunk in pits in the epidermis
- moist air trapped here lengthens the diffusion pathway
- reduces the evaporation rate
What does Leaf rolled
do as an adaptation for xerophytes?
- stomata inside and an inner surface covered in hairs
- traps moist air and prevents air movement across stomata
- reduces transpiration
What does Small leaves do as an adaptation for xerophytes?
- small, needle-shaped leaves
- reduce the surface area and therefore the evaporating surface
What does Extensive shallow roots do as an adaptation for xerophytes?
allow for the quick absorption of large quantities of water when it rains
What does thicken leaves or stems do as an adaptation for xerophytes?
contain cells that store water
What results in natural selection?
individuals that have the best adaptive features are the ones most likely to survive and reproduce
What do individual species show?
range of variation caused by differences in genes
What happens when species reproduce?
- produce more offspring than the environment is able to support
- competition for food and other resources which results in a ‘struggle for survival’
Which individuals have a high chance of survival and to reproduce?
characteristics most suited to the environment
What does more chances of survival and reproduce lead to?
- alleles resulting in these characteristics are passed to their offspring at a higher rate
- next generation, will hv greater number of individuals with the better adapted variations in characteristics
Who is survival of the fittest?
theory of natural selection was put forward by Charles Darwin
What happens if environment does not changes in adaptation?
selection does not change
what happens if environment changes in adaptation?
- a chance mutation produces a new allele,
- selection might now favor individuals with different characteristics or with the new allele
What Favours individuals when environment does not change?
same characteristics as their parents
What happens to individual that survive and reproduce?
- different set of alleles that they pass on to their offspring
- change in the characteristics of the species - it will produce evolution
Define evolution.
change in adaptive features of a population over time as a result of natural selection
What does natural selection result in?
process of adaptation
What happens as a result of evolution?
populations of organisms become better suited to their environment
What does selective breeding mean?
elect individuals with desirable characteristics and breed them together
Why does the selective breeding process not stop?
not all of the offspring will show the characteristics you want so offspring that do show the desired characteristics are selected and bred together
Does selective breeding process hv to be repeated?
repeated for many successive generations
What happens in natural selection?
- occurs naturally
- results in development of populations with features that are better adapted to their environment and survival
- usually take a longer time to occur
What happens in artificial selection?
- only occurs when humans intervene
- results in development of populations with features that are useful to humans and not necessarily to survival of individual
- take less time as only individuals with the desired features are allowed to reproduce
