Diversity and Selection

What are gene mutations?

• Involves a change in DNA base sequence

• This can result in the formation of new alleles

What types of mutations can happen?

• Substitution

• Insertion

• Deletion

What is a substitution mutation?

A mutation where one bases are substituted into DNA

For substitution mutations, why is it important that DNA is degenerate?

Since multiple triplets can code for the same amino acid, a substitution mutation will not always result in a mutation

What is the difference between harmful and beneficial mutations?

• Harmful mutations could be a detriment to an organism, decreasing it’s likelihood of survival so the gene dies out quickly

• Some mutations allow for organisms to be more adapted for survival purposes and so are beneficial and could increase in the population

What could be the effect of a substitution mutation?

• No effect- a Silent mutation

• Could cause a change in amino acid- hydrogen, ionic bonds and disulfide bridges formed in different places due to change in primary structure

  • Resulting protein is not functional or a different protein is made

• Could be beneficial or harmful

• A base in a triplet could code for a stop codon, making the polypeptide chain much shorter

Why are introns important for mutations?

Mutations in non-coding regions have no effect on protein synthesis

What is a deletion mutation?

A mutation where a base is completely removed from a DNA strand

What is an insertion mutation?

A mutation where a base is added into a gene

What is the effect of an insertion/deletion mutations?

• They cause a frame shift after the point where the mutation occurs

• Every amino acid downstream of the mutation will be effected

• These mutations, especially earlier in the gene, are more likely to be harmful

What causes mutations?

• They occur spontaneously all the time

• Mutagenic agents increase the rate of mutations such as ionising radiation, chemicals and some viruses

How many chromosomes do normal body cells have?

Cells have the diploid number of chromosomes (2n) meaning each cell contains 2 of each chromosomes- 1 paternal, 1 maternal

How many chromosomes do gametes have?

The have a haploid number of chromosomes (n)

Why gametes being haploid important?

• Because at fertilisation, the diploid number of chromosomes is restored

• The new combination of alleles increases genetic diversity and the ability of a species to survive a changing environment

What are homologous chromosomes?

Chromosomes carrying the same genes, on the same loci but may have different alleles

What happens in interphase of meiosis?

• Chromosomes replicate to form 2 sister chromatids joined at a centromere

• Chromosomes remain long and thin

What happens in prophase 1?

• Chromosomes condense and become visible

• Homologous pairs of chromosomes form a bivalent and non-sister chromatids exchange genes (crossing over)

• The spindle begins to form from the centrioles and the nuclear envelop breaks down

What happens in metaphase 1?

• Bivalents/homologous pairs of chromosomes pair up at the equator of the cell

• The position of homologous pairs is random which allows for independent segregation

What happens in anaphase 1?

Homologous chromosomes are pulled apart to opposite poles of the cell as spindle fibres contract

What happens at telophase 1 and cytokinesis?

• The chromosomes consisting of two chromatids joined at a centromere group together at opposite poles of the cell

• The spindle fibres disappear and the nuclear envelope reforms

• The cytoplasm divides producing two homologous haploid cells

What happens in prophase 2?

Spindle fibres form from centrioles in each cell

What happens in metaphase 2?

The chromosomes comprising of a pair of chromatids line up on the equator of the cell

What happens in anaphase 2?

• Centromeres divide

• Chromatids are pulled apart by spindle fibres to opposite poles of the cell

What happens in telophase 2/cytokinesis?

• Spindle fibres break down

• Nuclear envelope reforms around separated chromosomes

• Cytoplasm of both cells divides to produce 4 haploid gametes that are genetically different

What happens during crossing over?

• Occurs in prophase 1

• Homologous pairs of chromosomes associate to form a bivalent

• A chiasma forms where non-sister chromatids exchange alleles to from new allele combinations

What happens during independent segregation?

• Occurs in metaphase 1

• Random alignment of paternal and maternal chromosomes along the equator of the cell

• Results in new combinations of maternal and paternal chromosomes in the gametes formed

What is random fertilisation?

• Any egg can be fertilised any sperm so there is a huge number of combinations of different alleles

• This produces a zygote with different combinations of chromosomes and therefore different combinations of alleles

• This further increases genetic diversity

• Restores the diploid number of chromosomes

How can we find the different number of combinations of chromosomes in an organism?

No. of combinations to the power of the no. of pairs of chromosomes

What are plant lifecycles like?

• Plants can reproduce sexually or asexually

• A sexually reproducing plant will make a plant that reproduces asexually, then vice versa

• Each reproductive event creates a new generation that alternate types of reproduction and this is called alternation of generations

What are sporophytes and gametophytes?

• Sporophytes produced spores

• Gametophytes produce gametes

What can happen during chromosomes mutation and what does it lead to?

• There can be extra copies of a chromosomes or one copy missing

• It leads to inherited conditions because errors are present in gametes (hereditary cells)

What happens during the chromosome mutation, non-disjunction and what is an example of this?

• It is the failure of chromosomes to separate properly during anaphase

• An example of this is an extra copy of a 21 chromosome in humans leading to down syndrome

What does it mean for a species to have a high genetic diversity and how can this occur?

• There are many different alleles in a population

• This can happen by mutation or different alleles being introduced into a population when individuals from another population migrate into them- gene flow

What is a genetic bottleneck?

• An event that causes a big reduction in the population and large number of organisms die before reproducing

• It can also be an event where a small part of an original population becomes isolated for reasons such a geographical isolation or religion

• This reduces the no. of different alleles

• The survivors reproduce and a large population is creates from few individuals, and therefore the population has less alleles

What is the founder effect?

• Happens when a few individuals from a population start a new colony and there are only a small number of different alleles in the initial gene pool

• The frequency in each allele between the original population and the new colony may be very different

  • For example an allele that was rare may become very common, increasing chances of genetic disease

• This can be a result of migration which causes geographical separation or can be because of something like religion

What happens during natural selection?

• Mutations lead to different alleles in the population which increases genetic diversity

• Individuals with beneficial alleles are more likely to survive against selection pressures such as an environment or predation and therefore reproduce

• When the survivors reproduce, the next generation inherits the beneficial allele

• The next generation are more likely to survive and reproduce so the frequency of the allele increases from generation to generation

• Over time, the beneficial allele becomes increasingly common within the population

What is a selection pressure?

A factor that causes some organisms without beneficial characteristics to die off, and so individuals with beneficial characteristics are selected

What are the kinds of adaptations that can take place due to natural selection?

• Behavioural- organism actions that increase chance of survival and reproduction

• Physiological- processes inside an organisms body increasing it’s chances of survival

• Anatomical- Structural features of an organism’s body increasing it’s chances of survival

What is directional selection?

• Selection which favour one extreme of the population

• For example, bacteria carrying alleles for antibiotic resistance will be favoured and then will survive, passing on the alleles to the next generation until that allele becomes abundant

What is stabilising selection?

• Selection where the average characteristic is favoured

• For example, the birth weight of babies shows that babies born of average size have a much lower mortality ratee then very light or very heavy babies

What is disruptive selection?

Selection where two extremes are favoured over the average

What are some aseptic techniques?

• Regularly disinfect work surfaces

• Use sterile equipment and discard appropriately after use- sterilisation can be done with flame and ethanol or an autoclave

• Work near a Bunsen burner- hot air rises so microbes carried away from agar plate

• Minimise the time spent with the lid open off of the agar

• Flame neck of glass container of broth before and after use as this causes air to move out of the container, preventing unwanted organisms from falling in

What is phylogeny?

Study of evolutionary history of groups of organisms

How does selective breeding affect genetic diversity?

• Decreases

• Animals or plant bred for one or few specific desirable characteristics

What do phylogenetic trees show?

• It shows the relationship between the members of different species

• The point at which branches occur shows that two or more organisms share a common ancestor

• The first branch shows the common ancestor for all of the different species

• Closely related species will have diverge from one another from a recent common ancestor

What is taxonomy?

• Science of classification

• It involves naming some organisms and organising them into groups, making it easier to identify and study them

How are different groups of organisms classified?

• The are 8 groups called taxa, each one is called a taxon

• The order is domain, kingdom, phylum, class, order, family, genus, species

• As we descend, the organisms sharing in the groups are more closely related

• There are more groups at each level, but fewer organisms in each group

How are organisms grouped into a phylogenetic classification system?

• Species grouped on evolutionary relationships

• In a hierarchy with no overlap

What is a species?

A group of similar organisms able to produce and give fertile offspring

What is the binomial naming system?

• All organisms are given one internationally accepted Latin name containing two parts

• The first part is the genus with a capital letter

• The second part in the name of the species in lower case

• Name are always in italics are underlined

• This avoids confusion with using common names

What is courtship behaviour?

• Carried out to attract a mate of the right species

• This can vary from releasing chemicals to a series of displays

• This behaviour is species specific- only the individuals of the same species will recognise each other, making reproduction more successful and different species won’t produce fertile offspring

• Because of this, courtship can be used to classify organisms

How can genome sequencing be used to classify organisms?

• New technologies allow us to determine the base sequence of organism’s DNA

• The DNA of two organisms can be compared to see similarity

• The higher % similarity the DNA sequence orders share, the more closely related the species

• Organisms of the same species may have slightly different base sequences as they have different alleles

How can amino acid sequence be used to compare organisms?

• The sequence of amino acids is coded for by the sequence of bases in DNA

• Related organisms will have similar amino acid sequences as they have similar DNA base sequences

How can we use immunological comparison to classify organisms?

• Similar proteins will bind to the same antibodies

• Human serum injected into an animal like a rabbit

• The human antigens stimulate an immune response in the rabbit, so it produces anti-human antibodies

• If the antibodies are added to isolated samples of other species, any protein like the human version will bind to the antibody- this causes a precipitate to form

• The one that forms the least precipitate is the least related and vice versa

What happens during DNA hybridisation?

• DNA from two a different species is separated by heating it, breaking weak H bonds between bases

• The strands are mixed then cooled

• When base sequences are complimentary, H bonds reform between the separated strands forming hybrid DNA- 1 strand form each species

• DNA is the heated a second time to separate the hybrid strand again, and the temperature of complete separation is recorded

• The higher the temperature, the more similar the two species as more energy was needed to break more hydrogen bonds

How has gene technology affected the way genetic diversity is assessed?

• Before, genetic diversity would be measured by observable characteristics like eye colour

• Now we can measure this directly as different alleles will have slightly different DNA bases sequences leasing to slightly different amino acid sequences

• This is far more accurate than just observing different characteristics on the surface

What is biodiversity?

The variety of living organisms in an area/ecosystem/community

What is a community?

All the populations of different species in a habitat

What is species richness?

No. of different species in a community

What is the index of diversity and why is it used?

• Species richness only relies on the number of species, not on the sizes of the populations of all of those species

• Index of diversity takes both of these into account

What is variation and what is it caused by?

• The differences between individuals

• This can be caused by genetic or environmental factors

• Most variation is caused by a combination of both of these

Why do we use samples and how do we do it?

• Samples are used because they are far less time consuming to use than the whole population

• These samples have to be random so you could make a gird on the area you want to sample

• Then use a random number generator to pick a coordinate on the grid to sample

• We then have to use a statistical text to ensure that our findings are not just due to chance

What is standard deviation and what is it used for?

• The spread of data around the mean

• A large standard deviation shows a large variation, while a small SD shows a small variation

• You can use the SD to draw error bars on bar charts for example that extend above and below the maximum value

  • If the error bars overlap, it shows the difference between results is not significant

What is the equation for the index of diversity?

• N=Total no. of organisms of all species

• n=Total no. of organisms of one species

What do farmers do to increase farming space/yield that harms biodiversity?

• Woodland clearance- destroys many trees and the species residing in them, destroys habitats

• Hedgerow removal- turns lots of smaller fields into fewer large fields

• Pesticides- kills pests that feed on crops- loss of food sources

• Herbicides- kills unwanted plants (weeds), reduces the no, of organisms that feed on the weeds

• Monoculture- only growing one type of plant, supports fewer organisms

How can biodiversity be conserved?

• Legal protection to endangered species

• Protected areas

• Environmental stewardship schemes- encourage farmers to conserve biodiversity, like through growing more hedgerows

What are the biological advantages of hedgerows

• Hedgerows have a lot of biodiversity

• Birds can use them to nest

• Important wild flowers in hedges that could be used for medicines for example

• Animals use them for hunting and shelter

When collecting a sample, how should we know when to stop?

• We could calculate a running mean

• When this mean stays constant, we have enough values

What is the pentadactyl limb?

A limb with five digits (fingers or toes)

What are analogous characteristics?

• Characteristics that have the same function but have originated in different ways

• For example, wings on bats and birds

What are homologous characteristics?

• A characteristic shared by organisms in different groups originating from a common ancestor

• For example, the pentadactyl limb

What is horizontal gene transfer?

• When bacteria share their genes with other bacteria

• One bacteria share a plasmid through it’s pili