4B - Diversity, Classification and Variation Flashcards
What happens before meiosis starts?
- DNA unravels and replicates so there are two copies of each chromosomes (chromatids)
What happens after DNA unravels?
- DNA condenses to form double-armed chromosomes, each made from two sister chromatids
- sister chromatids are joined in the middle by a centromere
What happens during Meiosis I?
- chromosomes arrange themselves into homologous pairs
- homologous pairs are separated, halving the chromosome number
What happens during Meiosis II?
- pairs of sister chromatids that make up each chromosome are separated
- four haploid cells that are genetically different from each other are produced
In Meiosis I, the chromatids cross over, what does this mean?
- homologous pairs of chromosomes come together and pair up
- chromatids twist around each other and bits of chromatids swap over
- chromatids still contain same genes but have different combination of alleles
What two events during meiosis lead to genetic variation?
- crossing over
- independent segregation of chromosomes
How does independent segregation of chromosomes lead to genetic variation?
- when the pairs are separated, its completely random which chromosome from each pair ends up in which daughter cell
- shuffling of chromosomes leads to daughter cells having different combinations
What are the outcomes of mitosis?
- cells have same number of chromosomes as parent cell
- daughter cells are genetically identical to each other and parent cell
- produce 2 daughter cells
What are the outcomes of meiosis?
- cells have half the number of chromosomes as parent cell
- daughter cells are genetically different to each other and parent cell
- produce 4 daughter cells
What is meant by non-disjunction?
- failure of chromosomes to separate properly
- one type of chromosome mutation
What condition is caused by a person having an extra copy of chromosome 21?
- Down’s syndrome
What type of errors can occur in gene mutations?
- substitution - one base is substituted with another
- deletion - one base is deleted
What would happen if a mutation occurs in a gene?
- sequence of amino acids it codes for could be altered
Why won’t substitution always change the amino acid sequence?
- the degenerate nature of the genetic code means some amino acids code for more than one DNA triplet
Mutagenic agents increase the rate of mutations, give an example of a mutagenic agent?
- ultraviolet radiation
- ionising radiation
- viruses
What is meant by genetic diversity?
- number of different alleles of genes in a species or population
What increases genetic diversity within a population?
- mutations in DNA, form different alleles
- different alleles being introduced when organisms migrate and reproduce (gene flow)
What is meant by a genetic bottleneck?
- an event that causes a big reduction in a population
- reduces number of alleles in gene pool and reduces genetic diversity
- survivors reproduce
Describe the process of natural selection.
- those with the allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes
- a greater proportion inherits the beneficial gene
- next generation can then survive, reproduce and pass on their genes
- leads to evolution as the advantageous alleles become more common
What types of adaptations help organisms to survive in their environment?
- behavioural e.g. possums ‘play dead’ to escape predators
- physiological e.g bears lower their rate of metabolism to conserve energy in winter
- anatomical e.g whales have a thick layer of blubber which helps them keep warm in the cold sea
Antibiotic resistance shows directional selection. What is directional selection?
- individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
- could be in response to an environmental change.
How does directional selection work?
- some individuals have alleles that give them antibiotic resistance
- population is exposed to antibiotic, killing bacteria w/o resisting allele
- resistant bacteria survive and reproduce w/o competition, passing on allele to offspring
- most organisms in population will carry resistant allele.
Human birth weight shows stabilising selection. What is stabilising selection?
- individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
How does stabilising selection work?
- very small babies are less likely to survive; hard to maintain body temperature
- giving birth to large babies can be difficult; less likely to survive
- conditions are most favourable for medium sized babies
What aseptic techniques are used to prevent contamination of microbial cultures?
- regularly disinfect work surfaces
- work near Bunsen flame
- sterilise wire inoculation loop before and after each use passing through hot Bunsen flame for 5 secs
- briefly flame neck of glass container of broth just after its opened and just before its closed
- sterilise all glassware before and after use, also wash hands thoroughly before and after handling cultures
What is meant by phylogeny?
- study of evolutionary history of groups of organisms
What is meant by taxonomy?
- science of classification
- involves naming organisms and organising them into groups
What are the 8 groups in an evolutionary relationship heirarchy?
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
What is the binomial system?
- all organisms are given one internationally accepted scientific name in Latin that has two parts
What is each part of the Latin names of organisms?
- first part is genus, has capital letter
- second part is species, lower case letters
- e.g humans are Homo sapiens
What is courtship behaviour and how does it work?
- carried out by organisms to attract a mate of right species
- can be fairly simple or quite complex
- species specific
Why is it important that courtship behaviour is species specific?
- allows members of same species to recognise each other, preventing interbreeding and making reproduction more successful
How have gene technologies changed the way genetic diversity is assessed?
- allows us to measure genetic diversity directly
- give more accurate estimates of genetic diversity within a population
- allow genetic diversity of different species to be compared more easily
What is meant by biodiversity?
- variety of living organisms in an area
What is a habitat?
- place when an organism lives
What is a community?
- all the populations of different species in a habitat
What is local biodiversity?
- variety of different species living in small habitat that’s local to you
What is global biodiversity?
- variety of species on Earth
What is species richness?
- measure of number of different species in a community
What is meant by index of diversity?
- relationship between no. of species in a community and no. of of individuals in each species
How do you calculate index of diversity?
- d = N(N-1) / sum of n(n-1)
- N is total no.of organisms of all species
- n is total no.of organisms of one species
What are common agricultural practices which reduce biodiversity?
- woodland clearance
- hedgerow removal
- pesticides
- herbicides
- monoculture
How does woodland clearance and hedgerow removal reduce biodiversity?
- reduces number of trees and sometimes number of different tree species
- destroys habitats, means that species will die or migrate to another area
How do pesticides reduce biodiversity?
- directly killing pests
- species who eat pests will lose food source
How do herbicides reduce biodiversity?
- reduces plant biodiversity and could reduce no. of organisms that feeds on weeds
How does monoculture reduce biodiversity?
- single type of plant reduces biodiversity directly
- will support fewer organisms as a habitat or food source
What are examples of conservation schemes that protect biodiversity?
- giving legal protection to endangered species
- creating protected areas, restricts agricultural development
- Environmental Stewardship Scheme encourages farmers to conserve biodiversity
