genetic diversity Flashcards
what is a gene pool?
the sum total of all genes in an interbreeding population at a given time
what do random mutations do to the gene pool?
add new alleles to the gene pool and increase genetic diversity
What does natural selection and selective breeding do to the gene pool?
remove unwanted alleles and reduce genetic diversity
what causes interbreeding and where can it occur?
Results from the mating of closely related organisms.
could be due to a small population or as a result of selective breeding.
can occur in animals or plants
What can plants do in terms of natural interbreeding?
- natural interbreeds
- plants that normally self pollinate
- they can survive in small isolated populations
- also found in plant species which rapidly colonise new areas
what is outbreeding and example of an outbreeder?
results from mating of unrelated organisms, norm in nature
example: maize
What does outbreeding do?
ensures large genetic diversity, enables the population to adapt to environmental change.
what is inbreeding depression?
- results when deleterious recessive alleles accumulate
- organisms become homozygous for these alleles
- fitness is reduced / decline in vigour, size and fertility
what is genetic erosion?
factors that have contributed to the extinction of varieties and species of organisms. REDUCES GENETIC DIVERSITY
What causes genetic erosion?
- selective breeding
- modern agriculture
- growth of industry, towns and human population growth
why is it essential to maintain genetic diversity?
- So that if there is a new strain of disease or climate change a breeder can find a suitable parent organism with the appropriate (trait) allele for breeding
- Gene banks store genes as genomes of cells, tissues or whole organisms (not DNA store)
examples of gene banks
- seed banks
- sperm banks
- frozen embryos
- rare breeds of animals
what are the main threats to biodiversity of plants?
land conversion for:
- agriculture
- biofuels
- development
- palm oil
What are the aims of the millenium seed bank?
- Collect and store seeds of world’s seeds
- Collect 10% of the seeds of the world’s flora, particularly rare species and threatened species (endemic, endangered and economically important)
- Banks the seeds at Kew gardens and other countries AND use them
what are the main steps taken to preserve seeds?
- dry seeds (15 degrees, increases storage life/kills pests)
- seperate seeds and clean them
- Digital x-ray to capture image of internal structure to check they are healthy
- redry and store in sealed containers at -20 degrees
what is done to check that the seeds that are stored are surviving?
removed 100 seeds and try to germinate them
how many plants provide 80% of plants derived food? what crops are these?
12 plant species (8 cereal and 4 tubers)
what equipment is used to establish conditions for the germination of seeds?
Use incubators with different day and night temperatures to mimic the seeds being at the surface of the soil – will only start to germinate near the top of the soil under optimum conditions
What are recalcitrant seeds?
10% of seeds are recalcitrant - they can’t withstand the drying process
What techniques are used to store these varieties of plants?
- Take the growing point of a plant and put it in an alginate beed and store in liquid nitrogen at -196oC = cryopreservation
- To regrow them, defrost at 40oC and put into growth medium
What is the global importance of the Millenium seed bank project?
- prevent extinction of species
- largest collection of plant diversity
- use plants for climate change / new agriculture
- use seeds to reintroduce plants into natural habitats
what is the centre of diversity and where is it most often found?
Area that has the greatest genetic variation for a crop plant & its wild relatives. Usually found where a plant originated from
What is the benefit of keeping populations of rare breed animals?
Maintain a larger genetic diversity of alleles for future changes in consumer preferences, better adapted to climate change or emergence of new diseases
What are field gene banks and why are they needed to store genomes?
Fields, orchards, plantations, botanical gardens
Grow plants that have recalcitrant seeds
What is the main disadvantage of field gene banks?
take up a large space
List 4 advantages of gene banks storing sperm/embryos rather than whole animals.
- Occupy little space
- Minimal maintenance just a low temp.
- Long term storage
- Stored after death of animal
Outline the procedure for collecting and storing sperm in a sperm bank
- Collect sperm in artificial vagina and test for motility
- Dilute with an extender medium (albumen and citrate)
- Put into small containers/straws and freeze in liquid nitrogen at -196oC
Why are eggs more difficult to freeze than sperm?
- Larger
- Spherical (small sa:vol ratio) so take longer to cool down
- Freeze and thaw at different rates due to non-uniform cytoplasm
- Chromosomes are more fragile as meiosis not completed
Why is it essential that meristem cells are present in plant tissues used for plant tissue culture?
These cells retain the ability to divide and can differentiate into any cell type (are totipotent)
what are the stages of tissue culture?
- Take a small piece of stock plant with desirable characteristics. This is called an explant and should contain meristem cells
- add to disinfectant - sodium hypochlorite
- Place explant on sterile nutrient growth medium containing growth hormones to stimulate mitosis
- Cells in explant divide by mitosis to form a mass of undifferentiated cells called a callus
- After a few weeks the callus is divided and placed onto sterile nutrient media containing plant hormones (cytokinin) to stimulate shoot growth
- The clones are now called plantlets
- Plantlets are carefully planted into sterile soil and grown in a greenhouse
- Plants can then be planted outside
