Unit 6 - Inheritance, Variation And Evolution Flashcards
What is DNA
-stands for deoxyribonucleic acid
-contains coded information
-found in nucleus in structures called chromosomes
Structure of DNA
-polymer made up of repeating units called nucleotides
-each nucleotide consists of one sugar molecule, one phosphate molecule and one base
-sugar and phosphate molecules alternate
-one of 4 different bases join to each sugar (A, T, C, G)
-each base links to a base on the opposite strand
-A always pairs with T and C and G
-the order of the bases that decide the order of amino acids in a protein
-a double helix structure
What is a gene
-A gene is a small section of DNA on a chromosome
-each gene codes for a particular sequence of amino acids to make a specific protein
What is a genome
-Genome of an organism is the entire genetic material of that organism
-the whole human genome has now been studied and has great importance for medicine in the future
Human genome project important and what it is discovering
-allows scientists to identify genes in the genome that are linked to different types of diseases
-knowing which genes are linked to inherited diseases so we can develop effective treatments for them
-use them in tracing human migration patterns from the past
What is protein synthesis
-made in cytoplasm in ribosomes
-to make proteins, ribosomes use the code in the DNA (in the nucleus) and transfer it to the ribosomes
-this is done using a molecule called mRNA which acts as a messenger between the DNA and ribosomes
-amino acids would be brought to ribosome in correct order by carrier molecules
-the amino acids would then be joined together to make correct protein
How does the structure of DNA affect the protein made
-when a chain of amino acids has been assembled it folds into a unique shape which allows the protein to perform a specific task
Different examples of proteins and their functions
-enzyme (biological catalysts to speed up chemical reactions in the body)
-hormones (carry messages around the body)
-structural proteins (physically strong, collagen is an example that strengthens connective tissue)
What are mutations
-Changes to genetic code
-sometimes inherited or occur spontaneously
-most do not alter the protein and most have very little effect
-A few mutations code for an altered protein with a different shape. An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
-mutations change the sequence of the DNA bases in a gene which produces a genetic variant
-if there’s a mutation in non coding DNA it can change how genes are expressed
Different types of mutations that can occur
-insertions
-deletions
-substitutions
What is an insertion mutation
-Where a new base is inserted into a DNA base sequence where it shouldn’t be
-insertions change you way the groups of three bases are read which can change the amino acid they are coded for
What is a deletion mutation
-When a random base is deleted from the DNA base sequence
-they change the way the base sequence is read and have knock on effects further down the sequence
What is a substitution mutation
-When a random base in the DNA base sequence is changed into a different base
What is the relationship between DNA and proteins
DNA contains genes, each gene codes for a particular sequence of amino acids which are put together to make a protein
What is sexual reproduction
-Involves the fusion of male and female gametes
-Because there are two parents the offspring contains a mixture of their parents genes which leads to variation
-involved meiosis
What are the gametes fused in males and females in animals and plants
Animals = sperm and egg cell
Plants = pollen and egg cells
What is asexual reproduction
-Involves only one parent
-no fusion of gametes
-genetically identical offspring so no variation
-mitosis is involved (one cell divides into two identical cells)
-bacteria some plants and animals reproduce asexually
Process of meiosis
-before it starts to divide it duplicates genetic information
-cell divides twice
-you get four gametes each with a single set of chromosomes
-each gamete is genetically different from each other
Where does meiosis occur
In reproductive organs where gametes are being made
Process of mitosis
-DNA is copied
-cell must increase amount of mitochondria and ribosomes
-chromosomes are pulled apart
-nucleus divides
-cell membrane and cytoplasm divide
-two new daughter nuclei produced
-genetically identical cells
Advantages of sexual reproduction
-produces variation in offspring
-if environments changes variation gives a survival advantage by natural selection
-natural selection can be speeded up by humans in selective breeding to increase food production
Advantages of asexual reproduction
-only one parent needed
-more time and energy efficient as do not need to find a mate
-faster than sexual reproduction
-many identical offspring can be produced when conditions are favourable
Examples of organisms reproducing sexually and asexually
-malaria parasites reproduce asexually in the human host but sexually in the mosquito
-fungi reproduce asexually by spores but reproduce sexually to give variation
-many plants reproduce seeds sexually but also asexually by runner such as strawberry plants
What is a gamete
Reproductive sex cell
What are chromosomes
-thin strands of DNA
-carry genetic information from cell to cell
-they are subdivided into genes
-23 pairs of chromosomes in each human body cell
What is an allele
-different versions of the same gene
-For example, the gene for eye colour has an allele for blue eye colour and an allele for brown eye colour
What are dominant or recessive alleles
-A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype
-A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype
What is homozygous and heterozygous
-homozygous = alleles are both identical for the same characteristic, for example AA or aa
-heterozygous= alleles are both different for the same characteristic, for example Aa
What is the genotype
-the collection of alleles that determine characteristics and can be expressed as a
phenotype
What is the phenotype
-The visible characteristics of an organism which occur as a result of multiple genes
What are the female and male chromosomes
Female = XX (this combination allows female characteristics to develop)
Make= XY (Y chromosomes cause male characteristics)
Examples of characteristics which are controlled by a single gene
-fur colour in mice
-red green colour blindness in humans
What is cystic fibrosis and what is it caused by
-disorder of cell membranes ( lots of sticky mucus in air passages)
-caused by a recessive allele which means people with only one copy won’t have the disorder but they are carriers
What is polydactyl and what is it caused by
-having extra fingers and toes
-caused by dominant allele so can be inherited if just one parent carries the allele
What is embryo screening and what does it do
-during IVF before embryos are implanted in the womb you can remove a cell from each embryo and analyse its genes
-genetic disorders can then be detected
Advantages and disadvantages of embryo screening
A= stop people suffering , treating disorders costs the government and taxpayers money, there are laws to stop it going too far (people can’t choose sex of baby unless for health reasons)
D= implies that genetic problems are undesirable which could cause prejudice, may come a point where everyone wants to screen embryos so they can pick the most desirable one (blue eyes, blond hair), expensive
Three conclusions reached by Mendel
-characteristics in plants are determined by hereditary units
-hereditary units are passed on to offspring unchanged from both parents (one unit from each parent)
-hereditary units can be dominant or recessive
Why didn’t people accept Mendels work
-no one had any background knowledge to properly understand his findings
-after his death people realised the significance of it
-his work was a starting point that other scientists contributed to understanding the genes we have today
What is variation and the two types
-Differences in the characteristics of individuals in a population
-genetic variation and environmental variation
What causes variations
-genes they have inherited (genetic)
-conditions in which they have developed (environmental)
-combination of genes and the environment
Do mutations have an effect on the phenotype
-most have no effect on protein the gene codes for so most have no effect on phenotype
-some have small influence and only alter characteristics slightly
-very rarely mutations can result in a new phenotype, if the new phenotype is suited to an environmental change it can lead to rapid change in the species
What is evolution
Change in the inherited characteristics of a population over time through a process of natural selection which may result in a formation of new species
What is the theory of evolution
All of todays species of living things have evolved from simple life forms that first developed more than three billion years ago
What is natural selection (Charles Darwin’s ideas)
-referred to as survival of the fittest
-process where organism that are better adapted to an environment will survive and reproduce
-they will pass on genes to make their offspring successful
-beneficial characteristics become more common in population and the species evolve
How did Charles Darwin come up with his theories
As a result of a observations on an around the world expedition backed by years of experimentation and discussion and linked to developing knowledge of geology and fossils he suggested the theory of evolution by natural selection
Why was the theory of evolution only gradually accepted
-the theory challenged the idea that god made all the animals and plants that live on earth
-there was insufficient evidence at the time the theory was published to convince many scientists
-the mechanism of inheritance and variation was not known until 50 years after the theory was published
What was the book called that Charles Darwin published his ideas in
On the origin of species (1859)
What is environmental variation
-differences between members of same species that have been caused by environment or conditions something lives in
-examples = suntan, scars, accent
What is speciation
-phenotype can change so much because of natural selection that completely new species forms
-happens when population of the same species change enough to become reproductively isolated this means they can’t interbreed to produce fertile offspring
What is extinction and what causes it
-when no individuals of a species remain
-environment changes too quickly (destruction of habitat)
-new predator kills them (humans hunting them)
-new disease kills them
-can’t compete with another species for food
-catastrophic event (volcanic eruption)
Example = dodos (humans hunted them )
What was the work of Jean Baptiste Lamarck
-argued that changes that an organism acquires during it lifetime will be passed onto its offspring
-for example if a rabbit used its legs to run a lot to scape predators that it’s legs would get longer, the offspring of that rabbit will be born with longer legs
-his hypothesis was eventually rejected
What was the work of Alfred Wallace
-he published joint writing with Darwin which prompted Darwin to publish ‘on the origin of species’
-worked worldwide gathering evidence for evolutionary theory
-best known for his work on warning colouration in animals and his theory of speciation
One cause of genetic variation in a population other than mutations
Sexual reproduction
What is selective breeding
-process by which humans breed plants and animals for particular genetic characteristics
-humans have been doing this for hundreds of years
-they are selectively bred to develop features that are useful or attractive
Examples of selective breeding
-animals that produce more meat or milk
-crops with disease resistance
-dogs with gentle nature
-large or unusual flowers
Process of selective breeding
-choosing parents with desired characteristics from a mixed population
-breed them together
-select the best offspring and breed them together
-continue this over several generations until all the offspring show the desired characteristic
Disadvantages of selective breeding
-can cause Inbreeding (reduction in number of different allele) where some breeds are particularly prone to disease or inherited defects
-if new disease appears there is little variation, so if one of them is killed by it the others are likely to as well
What is genetic engineering and an example
-Process which involved modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
-plants crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits
How have bacteria been genetically engineered
-to produce useful substances such as human insulin to treat diabetes
Process of genetic engineering
-useful gene is isolated (cut) from one organisms genome using enzymes and is inserted into a vector
-this vector is usually a virus or bacterial plasmid depending on type of organism that the gene is being transferred to
-when vector is introduced to target organism the useful gene is inserted into its cells
Advantages and disadvantages of genetically modified crops
A= can increase yield making more food, people in developing nations often lack nutrients so can be engineered to contain nutrients, GM crops are being grown in some places without any problems
D= affect number of wildflowers and therefore insects around crops (reducing farmland biodiversity), concerns about safety and the effects of eating them on human health- they may develop allergies
What is cloning tissue culture and why is it important
-using small groups of cells are out in growth medium with hormones to grow into identical new plants
-can be made very quickly in very little space and can be grown all year
-this is important for preserving rare plant species or commercially in nurseries
What is cuttings (cloning)
-older but simpler method used by gardeners
-gardeners take cuttings from good parent plants and then plant them to produce identical copies of the parent plant
-these plants can be produced quickly and cheaply
What is embryo transplants (cloning)
-splitting apart cells from a developing animal embryo before they become specialised
-then transplants the identical embryos into host mother
-this means that you can produce the “ideal” offspring
What is the process of adult cell cloning
-the nucleus is removed from an unfertilised egg cells
-the nucleus from an adult body cell such as a skin cell is inserted into the egg cell
-an electric shock stimulates the egg cell to divide to form an embryo
-these embryo cells contain the same genetic information as the adult skin cell
-when the embryo has developed into a ball of cells, it is inserted
Issues surrounding cloning
-reduced gene pool this means fewer different alleles in a population, so if a new disease appears they could all be wiped out
-animals may not be as healthy as normal ones
-some people worry that human may be cloned in the future, if allowed any success may follow unsuccessful attempts
Advantages of cloning
-could lead to greater understanding of the development of the embryo and of ageing and age related disorders
-could be used to preserve endangered species
What are fossils
-remains of organisms from millions of years of years ago which are found in rocks
-we can learn from sous-sols how much or how little different organisms have changed as life developed on Earth
What are the 3 ways fossils may be formed
-from parts of the organisms that have not decayed because one or more of the conditions needed for decay are absent
-when parts of the organism are replaced by minerals as they decay
-as preserved traces of organisms such as footprints, burrows and rootlet traces
Why is the fossil record incomplete
-many early forms of life were soft bodied which means that they have left few traces behind
-what traces there were have been destroyed by geological activity (movement of tectonic plates)
-this is why scientists cannot be certain about how life began on Earth
What was later discovered due to Mendels work
-it was observed that chromosomes and Mendels ‘units’ behaved in similar ways
-this led to the idea that the ‘units’ now called genes were located in chromosomes
What 2 things can lead to speciation
-isolation
-natural selection
Why can isolation lead to speciation
-population of species are separated
-this can happen due to physical barrier (flood or earthquake)
-conditions will be different on either side of barrier (different climates)
-because environment is different, different characteristics will become more common in each population due to natural selection
-individuals from different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring
How does natural selection lead to speciation
-because each population shows genetic variation they will have a wide range of alleles
-in each population individuals with characteristics that make them better adapted to their environment has a better chance of survival and reproducing successfully
-so the alleles that control beneficial characteristics will be passed onto next generation
What is resistant bacteria and how does it spread
-bacteria can evolve rapid because they replicate at as fast rate
-mutations of bacterial pathogens produce new strains
-some strains might be resistant to antibiotics and so are not killed
-they survive and reproduce
-so population of resistant strain rises
-resistant strain will then spread because people are not immune to it and there is no effective treatment
What is an example of resistant bacteria
MRSA - often affects people in hospitals and can be fatal if enters bloodstream
What can you do to reduce the rate of development of antibiotic strains
-doctors should not prescribe antibiotics inappropriately, such as treating non serious or viral infections
-patients should complete their course of antibiotics so all bacteria is killed and none survive to mutate and form resistant strains
-agricultural use of antibiotics should be restricted
Problems with the development of new antibiotics
-it is a costly process
-slow so we are unlikely to keep up with the demand for new resistant strains
What is classification of living organisms and who developed it
-living organisms have been classified into groups depending on their structure and characteristics in a system
-this system was developed by Carl Linnaeus
What are groups the organisms they are classified in (in order)
-kingdom
-phylum
-class
-order
-family
-genus
-species
How and why has the classification methods developed over time
-as evidence of internal use more developed due to improvements in microscopes and understanding of biochemical processes progressed new models were proposed
Who developed the new classification system and what is it
-Carl Woese
-it is a three domain system
-in this system organisms are divided into : Archaea, bacteria and eukaryota
What is Archaea, bacteria and Eaukaryota (all part of Woese three domain system)
-Archaea = primitive bacteria usually living in extreme environments such as hot springs
-bacteria = true bacteria like E. coli
-Eukaryota = B-road range of organisms including protists, fungi, plants and animals
How are organisms named according to the binomial system and why is it used
-every organism is given a two part Latin name
-the first part refers to the genus that the organism belongs to
-the second part refers to the species
-can be used worldwide as scientists in different countries who speak different language all refer to the same name avoiding confusion
What are evolutionary trees
-show how different species are related to each other
-the more recent the common ancestor, the more closely related the two species and the more characteristics they share
-they use current classification data for living organisms and fossil data for extinct organisms
