Flashcards in Inheritance, variation and evolution Deck (119):
What does DNA stand for?
What is DNA?
A chemical that all the genetic material in a cell is made from: contains coded information to put an organism together and make it work
What is a gene?
A small section of DNA found on a chromosome that codes for a articular sequence of amino acids which are put together to make a specific protein
How many amino acids are used in DNA
20 but they make up thousands of different proteins
What is a genome?
The name for the entire set of genetic material in an organism
Why is understanding the human genome important for science and medication?
It can help associate a particular gene to a disease it causes, allowing a more effective treatment to be found and it can show where people originated from, helping scientists understand why populations split off
What are nucleotides?
Repeating strands making up the polymer in DNA, made up of one sugar molecule, one phosphate molecule and one 'base'
Describe the structure of a nucleotide
The sugar and phosphate molecules form a 'backbone' to the DNA strands and they alternate. One of four different bases (A, T, C or G) joins to each sugar.
How are the bases arranged on a DNA molecule?
Each base links to a base on the opposite strand on the helix; A always pairs up with T and C always pairs up with G (called complementary base pairing)
What depends on the order of bases in a gene and why?
The order of the amino acids which join together to make various proteins as each amino acid is coded for by a sequence of three bases in the gene
What do the parts of DNA that don't code for proteins do?
They switch genes on and off, so they control whether or not a gene is expressed
Where are proteins made?
In the cell cytoplasm on tiny structure called ribosomes
How are proteins made?
The ribosomes use the code from DNA, which is transported from the nucleus to the ribosomes by using a molecule called mRNA (which is made by copying the code from DNA). The mRNA carries the code the ribosomes in the correct order
Give three examples of proteins in the body
Enzymes as biological catalysts, hormones to carry messages and structural proteins to be physically strong
What is a mutation?
A random change in an organism's DNA which can sometimes by inherited and occur both continuously and spontaneously
How can the chance of mutation be increased?
By exposure to certain substances or some types of radiation
How do mutations change DNA?
It changes the sequence of bases in a gene, producing a genetic variant, which could lead to a change in the maino acids and therfore the proetin it codes for
How can a mutation affect a protein?
Most mutations have very little or no effect on the protein, however, it can sometimes change the shape which can prevent it from performing it's function
Give two examples of proteins which can be effected by mutations
Enzymes as is the shape of the active site is changes, the substrate can no longer bind to it and structural proteins can loose their strength if their shape is changed
What is an insertion?
Where a new base is inserted into the DNA base sequence where it shouldn't be
How can insertions affect the DNA?
It changes the way the groups of three bases are read, which can change the amino acids which they code for. This can potentially have a knock on effect with bases further on in the sequence
What are deletions?
When a random base is deleted from the DNA base sequence
How can deletions affect DNA?
They can affect the way base sequences are read, giveing a knock-on effect
What are substitutions?
Mutations where a random base in the DNA base sequence is changes to a different base
What is sexual reproduction?
Where genetic information from two different organisms is combined to produce offspring which are genetically different to either parent. It involves the fusion of male and female gametes, giving the offspring a mixture of both parent's genes
What are the features of sexual reproduction?
Mother and father produce gametes by meiosis, (in humans) each gamete contains 23 chromosomes, egg and sperm fuse together to form a cell with full number of chromosomes and produces variation in offspring,
What is asexual reproduction?
Reproduction with only one parent and the offspring are genetically identical to the parent
What are the features of asexual reproduction?
Happens by mitosis (cell making a new cell by dividing in two), new cell has exactly same genetic information and is done by bacteria, some plants and some animals
Where does meiosis happen in humans?
In the reproductive organs
Give the process of meiosis
Cell duplicates genetic information, chromosomes arrange into pairs, in first division chromosome pairs line up in centre of cell, pairs are pulled apart, each new cell gets one copy of each chromosome, both parent's chromosomes go into each cell, in second division chromosomes line up in centre of cell and the arms of chromosomes are pulled apart
What are the exact products of meiosis?
Four gametes, each with a single set of chromosomes in it. Each of the gametes is genetically different from the others because the chromosomes all get shuffles up during meiosis and each gamete only gets half of them
How does the cell produced by gamete fusion replicate itself?
The resulting new cell from meiosis divides by mitosis to make a new copy of itself many times to produce lots of many cells in an embryo. These cells then start to differentiate into the different types of specialized cells that make up a whole organism
What are the advantages of sexual reproduction over asexual reproduction?
There is variation in offspring, increasing chance of survival in a change in an environment (natural selection)
What is selective breeding?
Where individuals with desirable characteristics are bred to produce offspring that have the desirable characteristics too
What advantages can selective breeding give?
It speeds up natural selection, produces animals with desirable characteristics and can increase food production
What are the advantages of asexual reproduction over sexual reproduction?
There only needs to be one parent, uses less energy as organisms don't need to find a mate, faster and many identical offspring can be produced in favourable conditions
When does malaria reproduce both sexually and asexually?
The parasite produces sexually when in the mosquito and asexually when in the host
When does fungus (some species) reproduce both sexually and asexually?
Asexually produced spores are produced normally and make a genetically identical plant, but if the fungus is experiencing an unfavourable change to the environment, the spores will be produced sexually to introduce variation the the population
How do strawberry plants reproduce sexually?
They produce stems that grow on the surface of the soil away form the plant (a runner). At various points along the runner, a new strawberry plant forms that is identical to the first plant
How many chromosome pairs are there in each human cell and what do they do?
23, 22 of these are matched pairs which control characteristics but the 23rd pair decide sex
How do chromosomes determine gender?
Males have an XY chromosome pair; the Y chromosome causes male characteristics. Females have an XX chromosome pair; the XX combination allows female characteristics to develop
How are sperm cells given X and Y chromosomes?
When making sperm, the X and Y chromosomes are drawn apart in the first division in meiosis. There's a 50% chance it gets an X-chromosome and a 50% chance it gets an Y-chromosome
What is an allele?
A different version of the same gene; you have two versions of every gene in your body, one on each chromosome in a pair
What is a homozygous trait?
If an organism has two alleles for a particular gene that are the same, then it's homozygous for that trait
What is a hetrozygous trait?
If an organism has two alleles for a particular gene that are the different, then it's hetrozygous
What are dominant and recessive alleles?
If the two alleles are different, only one can determine what characteristic is present. The allele for the characteristic that is shown is the dominant one and the one that is not is the recessive
What is your genotype?
The combination of alleles you have
What is your phenotype?
Your alleles working at a molecular level to determine what characteristics
What is cystic fibrosis?
A genetic disorder of cell membranes which results in the body producing a lot of sticky mucus in the air passages and the pancreas
What is a carrier?
With a recessive gene, people that have only one copy of it will not inherit the characteristic but can pass it on
How does a child get cystic fibrosis?
The allele which causes cystic fibrosis is carried by 1 in 25, so for the child to have the disorder, both parents must either have both parents as carriers or have the disorders as themselves
What is polydactyly?
A genetic disorder where a baby is born with extra fingers or toes
How does a child get polydactyly?
The disorder is caused by a dominant allele and so can be inherited if just one parent carries the defective allele (who will also have the condition)
How can embryos be screened for genetic disorders?
Either from IVF or an embryo in the womb, DNA can be taken and it's genes be analysed, allowing genetic disorders to be detected
What are the arguments against embryonic screening?
After screening, a pregnancy could be terminated or in IVF an embryo could be thrown away, it implies people with genetic conditions are 'undesirable', people may want to screen embryos so that they can pick 'desirable' physical characteristics and it is very expensive
What are the arguments for screening?
It will help stop suffering, treating disorders costs the government a lot of money and there are laws to stop it going too far (parents cannot even select the sex of their baby)
Who was Gregor Mendel?
An Austrian monk who trained in mathematics and natural history. He is known for his work on genetics
What did Gregor Mendel discover?
He noted how characteristics in plants were passed on from one generation to the next: he had shown that the height characteristics in pea plants was determined by separately inherited "hereditary units" passed on from each parent. The ratios of tall and dwarf plants showed that the unit for tall plants was dominant over the unit for dwarf plants
What were Mendel's three important conclusions?
Characteristics in plants are determined by 'hereditary units', hereditary units are passed on to offspring unchanged from both parents (one from each parent) and that hereditary units can be dominant or recessive
Why did people not properly understand Mendel's findings originally?
They had no idea about genes, DNA and chromosomes
How has Mended's work contributed to the understanding of genes which we have today?
Scientists in the late 1800s were able to observe how chromosomes behaved during cell division, scientists in the early 20th century realised how similarities in the way that chromosomes and Mendel's 'units' acted and in 1953, the structure of DNA was determined
What is variation?
Organisms of the same species having differences
What are the two types of variation?
Genetic variation and environmental variation
What causes genetic variation?
As most animals gene some genes from the mother and some form the father, the offspring produced is genetically identical
What characteristic are controlled only by genes?
In animals, this includes eye colour, blood group and inherited disorders
How are characteristics influenced by the environment?
This is called environmental variation, e.g. a plant grown in the sun would be luscious and green
What are most characteristics determined by?
A mixture of both genetic and environmental factors e.g. the maximum height of a plant is determined by it's genes, but whether it reaches that height is determined by it's environment
How do mutations introduce variation?
Although it's very rare, mutations can result in a a new phenotype being seen in a species.
What is the theory of evolution?
All of today's species have evolved from simple life forms that first started to develop over three billion years ago
What resources did Darwin use to come up with the theory of natural selection?
The observations he made on a huge round-the-world trip, along with experiments, discussions and new knowledge of fossils and geology
How did Darwin come up with 'survival of the fittest' theory?
He knew that species had wide phenotype variation and also that there was competition, which allowed him to conclude that the most suitable characteristics for an environment would be more successful competitors and more likely to survive
What is the natural selection theory?
Successful organisms are more likely to reproduce and pass on the successful characteristics and over time, the beneficial changes become more common in the population and the species changes
How have new discoveries helped Darwin's theory?
He could not give a good explanation how or why new characteristics were made and passed on. Now, we know that phenotype variation is controlled by genes and happens because of random mutations
What is speciation?
After a long time, the phenotypes of organisms can change so much because of natural selection that a completely new species is formed
Why can species become extinct?
The environment changes too quickly, a new predator kills them , a new disease kills them, they cannot compete with another species for food or a catastrophic event happens which kills them all
Why did people at the time not agree with Darwin?
It went against religious beliefs about how life on earth develops, Darwin couldn't explain why the characteristics appeared or how they were passed on and there wasn't enough evidence to convince other scientists
What was Lamarck's theory?
Changes that an organism acquires during it's lifetime will be passed on to it's offspring: he thought that is a characteristic was used a lot by an organism, then it would become more developed during it's lifetime and the offspring will inherit the acquired characteristic
Why was Lamarck's hypothesis eventually rejected?
Experiments did not support it and the discovery of genetics supported Darwin's idea instead. It was also supported by the discovery of different fossils
Why do scientists have different hypotheses to explain similar observations?
They have different beliefs, or they have been influenced by different people, or they think differently
What is selective breeding?
When humans artificially select the plants or animals that are going to breed so that the genes for a particular characteristic remain in the population
What types of organisms would be selectively bred and why?
Animals with more meat or milk, crops with disease resistance, dogs with a good temperament and decorative plants with big or unusual flowers
What is the basic process used in selective breeding?
Select the stock with the desirable characteristics, breed them together, select the best offspring, breed them together then continue this process over several generation so that the trait gets stronger and more have it
What is the main drawback with selective breeding?
It reduces the gene pool: the number of different alleles in a population. This is because the ones being bred are often closely related, known as inbreeding
Why is inbreeding not good?
There is a higher chance of the offspring inheriting harmful genetic diseases and if a new disease appears, because there is not much variation in the population, there is a lower chance that there are any resistant alleles present in the poplulation
What is the basic idea of genetic engineering?
To transfer a gene responsible for a desirable characteristics from one organism's genome into another organism, so that it has the desired characteristic
How is genetic engineering performed?
A useful gene is isolated from one organism's genome using enzymes and inserted into a vector (usually a virus or bacteria plasmid), the vector is then introduced to the target organism, inserting the useful gene into it's allele
Give four examples of genetic engineering
Bacteria have been modified to produce human insulin, GM crops can be better quality to resistant to pests, sheep have been modified to produce substances in milk that can be used to treat diseases and scientists are researching genetic modification treatments for inherited diseases
Why is genetic engineering a controversial topic?
There are worries about the long term effects as changing an organisms genes could potentially create unplanned problems
What are the disadvantages of GM crops?
It could reduce farmland biodiversity, not everyone is convinced they are safe and transplanted genes could get into the natural environment e.g. a herbicide resistance gene may be picked up by weeds
What are the advantages of GM crops?
They can increase the yield, the can be engineered to contain the nutrient that is missing and they are already being grown in some places, with no problems detected
What is tissue culture?
Where a few plant cells are put in a growth medium with hormones, and they grow into clones of the parent plant. These plants can be made very quickly, in little space, all year
What is tissue culture used for?
By scientists to preserve rare plants that are hard to reproduce naturally and by plant nurseries to produce lots of stock very quickly
What are cuttings used for?
Gardeners take cuttings from good parent plants then plant them to produce genetically identical copies of the parent plant, which are produced quickly and cheaply
How can animal clones be made using embryo transplants?`
Sperm and egg cells are taken from prize bulls and cows, they are artificially fertilised, the embryo formed is split many time before any cells are specialized then these are implanted into lots of other cows
How is adult cell cloning used to make clones?
The nucleus is removed from an unfertilised egg cell, the nucleus from an adult body cell is removed then inserted into the embryo, it is electrically shocked to make it divide. This is then implanted into the womb of a female
What are the issues surrounding cloning?
You get a reduced gene pool (easier for a disease to wipe them out), the cloned organisms may not be as healthy as regular ones and some worry that humans may be cloned in the future
What are the benefits of cloning?
The study of animal clones could lead to greater understanding of the development of the embryo, ageing and age-related disorders and it could also be sued to preserve endangered species
What are fossils?
The remains of organisms from many thousands of years ago which are found in rocks, providing evidence that organisms lived ages ago
What can fossils tell us?
How much or how little organisms have evolved over time
How do fossils form from gradual replacement by minerals?
Things like bones ect. which don't decay easily are buried, then replaced by minerals as they decay, forming a rock like substance shaped like the original remains. the surrounding sediments also turn to rick, but the fossil stays distinct inside the rock
How do fossils form from casts and impressions?
An organism is buried in soft material like clay, which later hardens around it, so the organism decays, leaving a cast of itself. Things like footprints can also be preserved in this way
How do fossils form from preservation in places where no decay happens?
In amber and tar pits, there's no oxygen or moisture so decay microbes cannot survive. In glaciers, it is too cold for them and peat bogs are too acidic. In these places, when an organism dies, it will be preserved as it's body will not be decayed
What are the main hypotheses of how life began on earth?
Life forms came into existence on a primordial swamp or under the sea on earth and simple organic molecules were brought to earth on comets which then became more and more complex until they were lifeforms
Why can't hypotheses about how life began on earth be supported or disproved?
There's a lack of evidence: many early life-forms were soft-bodied which often decays completely and fossils that dis form millions of years ago may have been destroyed b geological activity
When does speciation occur?
When populations of the same species become so different that they can no longer successfully interbreed to produce fertile offspring
Describe the process of speciation
Two populations of the same species become isolated by a physical barrier, conditions on either side are different, random mutations cause variation, those with characteristics more suited to the environment are more likely to survive, alleles that control beneficial characteristic more likely to be passed on to offspring, individuals from different populations will eventually have changed so much that they can no longer successfully interbreed
Who was Alfred Wallace?
A scientist at the same time as Darwin working on the idea of speciation
How did Wallace's ideas contribute to the understanding of speciation today?
He worked on the idea of natural selection with Darwin (prompting him to publish 'On the Origin of Species') and he provided lots of evidence to support the theory of evolution by natural selection
How can bacteria become antibiotic-resistant?
Bacteria sometimes develop random mutations, including being less affected by an antibiotic. This can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance become more common in the population
Why are antibiotic-resistant bacteria a problem for people?
People aren't immune to the new strain and there is no effective treatment, meaning that the infection can easily spread between other people
Give an example of a common 'superbug'
MRSA, it is very hard to get rid of. often affects people in hospitals and can be fatal if it enters their bloodstream
Why is it important to take a full course of antibiotics?
It makes sure that ALL the bacteria are destroyed, meaning that there are none left to mutate and develop into antibiotic-resistant strains
Why is there concern about the overuse of antibiotics in agriculture?
Antibiotics can be given to animals to prevent them from becoming ill and make them grow faster, leading to the development of antibiotic-resistant bacteria which can the spread to humans
What is classification?
Organising living organisms into groups
What is the Linnaean system?
Living things are first divided into kingdoms, which are then subdivided into smaller and smaller groups: phylum, class, order, family, genus and species
Why do classification systems change over time?
Knowledge of the biochemical processes taking place inside organisms has developed and microscopes have improved
What is Carl Woese's three-domain system?
Orgainsims are first split into three large domains: archaea for primitive bacteria, bacteria for true bacteria and eukaryota which includes organisms such as fungi, plants, animals and protists. They are then divided into smaller groups: kingdom, phylum, class, order, family, genus and species
What is the bionomial system?
Every organisms is given it's own two-part Latin name, the first part refers to the genus the organism belongs to and the second part refers to the species