inheritance and variation Flashcards

Question

what are genes?

Answer 1

small sections of DNA (basically a small segment of a chromosome). each gene codes for a specific sequence of amino acids to make a specific protein, as they're each a particular sequence of bases (determines what type of cell is formed), which include the formation of the enzymes that control cell chemistry.

Answer 2

the complete genetic makeup/profile of a person. their entire genetic material. - includes DNA found in the chromosomes (DNA from both the mother and the father), and DNA found in the mitochondria (DNA from just the mother, as it comes from the mitochondria of the egg) - each human (apart from identical twins) has a unique genome, meaning they have slightly different combinations of proteins inside of them, so they have different phenotypes

Answer 3

- in 2003, scientists from across the globe working together announced they'd worked out the entire human genetic code. - the first sequence of the human genome took over 10 years to produce, now it only takes 2 weeks. - they have now sequenced over 1000 people's genomes, and the aim is to find out as much as possible about human DNA. - from 1990 to 2003, scientists globally worked together to sequence all 3 billion DNA base pairs that make up the human genome. they have identified around 20,500 human genes and so far found about 2,000 genes linked to disease

Answer 4

- the information in the genome could tell you whether you're at an increased risk of a particular disease, as we know the specific gene that are linked to certain diseases e.g. cancer (there are genes linked to an increased risk of developing disease) and helps us to understand inherited disorders. we can then overcome them by medicine or by repairing faulty genes. - new personalised drugs and therapies can be tailored to a patient's specific genetic makeup - we can predict the risk of an inherited disorder for an individual, so they can make lifestyle choices to reduce this risk. people can get screened to detect health risks early and start treatment sooner

Answer 5

people across the world can be linked by their DNA patterns, allowing scientists to trace human migration patterns since ancient history, and link us to our ancestors - we all share most of our genomes, but the small differences between different populations can tell us when they separated

Answer 6

- there are over 3 billion base pairs - there are 21,000 genes that code for proteins - you can make many different proteins from the same gene, by switching different parts of it on and off

Answer 7

- learning about one's genetic risks can cause stress and mental health issues - genetic discrimination may lead to unfair treatment in jobs and insurance for those with certain gene variants. strict regulations are needed to prevent gene-based bias - there are concerns about the misuse of genetic data by employers and insurers, emphasising the need for privacy protections

Answer 8

- phosphate group (little molecule attached to large ribose) - ribose/sugar (large molecule in the middle) - nitrogenous base (medium sized molecule attached to the ribose on the other side). this nitrogenous base is either the letter A, T, C, or G, which is what makes each base different. - every nucleotide has exactly the same phosphate and sugar

Answer 9

the phosphate of one nucleotide bonds to the sugar of the other nucleotide, and this forms a long chain, called a sugar-phosphate backbone - this effectively forms a protective outer casing around the central bases - the bases in the middle can then pair up with another polymer strand, holding them together

Answer 10

A = Adenine C = Cytosine T = Thymine G = Guanine A and T go together, C and G go together (apple in the tree, car in the garage) - these are called complementary base pairs

Answer 11

the sequence of bases

Answer 12

polymers of amino acids. contain hundreds of amino acids joined together. there are 20 different amino acids in humans. the specific order and type of amino acids determines the shape of the protein. this determines its function (e.g. enzyme, structural protein, hormone). - the order of amino acids in a protein is determined by the sequence of bases in the gene for that protein.

Answer 13

the cell reads the DNA sequence as triplets of bases. each triplet encodes for a specific amino acid in the protein. these amino acids form a long chain (a polypeptide), and this long chain can fold up into a specific protein, with a specific shape and function

Answer 14

TRANSCRIPTION - the enzyme RNA polymerase binds to the DNA just before where the gene starts - just ahead of this enzyme, the two strands of DNA separate, so their bases are exposed - the RNA polymerase moves along the bases and reads them one by one (this is a template strand), using them make an mRNA strand (the mRNA bases will be complementary to the DNA bases) - the DNA will then close up after the RNA polymerase has passed over it, so only a small section of DNA is ever exposed - once the RNA polymerase is finished, it detaches from the DNA, and the DNA can close back up - we're left with an mRNA that's free to leave the nucleus and head to the ribosome

Answer 15

TRANSLATION - the mRNA molecule binds to a ribosome, and the ribosome is now ready to start building the protein. - the amino acids are brought to the ribosome by tRNA (transfer RNA). these molecules have the amino acid at the top, and an anti-codon at the bottom - a sequence of three bases complementary to the three bases on the mRNA. it's these three bases on the mRNA that code for the amino acid on the tRNA - the ribosome moves along and the process repeats, and the first tRNA molecules can detach, leaving the amino acid - the amino acid chain will now detach from the ribosome once the protein chain/polypeptide (of amino acids in the correct order) is complete, it's bound together by the ribosome and it folds into its unique shape. the shape enables the protein to do its specific job.

Answer 16

each type of tRNA molecule is specific to a particular triplet on the mRNA, so we know it always brings down the correct amino acid

Answer 17

DNA mRNA Cytosine - Guanine Guanine - Cytosine Thymine - Adenine Adenine - Uracil (the mRNA doesn't have a thymine base, it's instead replaced with a uracil base, represented by a U)

Answer 18

take a copy of the gene (on mRNA), as the entire DNA strand can't leave the nucleus to access the ribosome (outside of the nucleus).

Answer 19

1. mRNA is much shorter than DNA (only a single gene long) 2. only a single strand, rather than a double strand 3. doesn't contain the base thymine, and instead uracil

Answer 20

- enzymes - hormones - structural proteins (adds strength to cells and tissues)

Answer 21

we have two copies of each chromosome (1 from each parent). therefore, we have 2 copies of each gene. therefore we have two alleles. they can be the same allele, or different - one chromosome in the pair comes from the father, and the other comes from the mother. ALLELES ARE BASICALLY THE DIFFERENT VERSIONS OF A GENE.

Answer 22

1. chromosomes are the biggest. they are molecules made up of many coiled up sections of DNA. 2. DNA is responsible for building and maintaining your human structure. 3. genes are segments/sequences of your DNA, that code for certain characteristics.

Answer 23

- one causes blue eyes. the recessive gene (b), meaning there's less of a chance as you need two, not just one. - one causes brown eyes. the dominant gene (B), meaning there's a greater chance as you only need one.

Answer 24

where the two alleles are the same. (e.g. a bb person is homozygous for the blue eye allele).

Answer 25

where the two alleles are different. (e.g. Bb is heterozygous, as there's one blue eye and one brown eye allele).

Answer 26

it tells us which alleles a person has for a particular gene (tells us the entire collection of alleles that are present). (e.g. a person with 2 copies of the blue eye allele has the 'bb' genotype).

Answer 27

a characteristic caused by a particular genotype. (e.g. a 'bb' genotype causes blue eyes. blue eyes is the phenotype).

Answer 28

- a dominant allele always produces its characteristic, even if there's only one in the genotype. represented with an upper-case letter. - recessive alleles (represented with lower-case letter) only produces its characteristic if both of the alleles in the genotype are recessive.

Answer 29

XY = male XX = female

Answer 30

discovered structure of DNA. realised it's made up of two chains of nucleotide pairs that encode genetic information. - used Rosalind Franklin's image of DNA to make their discovery.

Answer 31

- the discovery of the structure of the DNA was made possible by her X-ray diffraction work with Wilkins, although he took the credit for it and she didn't. - she created Photo 51, where in her x-ray diffraction work, the lighter diamond shapes above and below the darkened x suggested a double helix pattern. provided a lot of structural information about DNA. - she was unaware that Wilkins, Watson, and Crick had used her x-ray photograph, so they didn't have permission to use her data. they excluded her from winning the Nobel prize.

Answer 32

- found that in DNA, the ratios of A to T and G to C are equal. provided clues into the chemical pairings that made up DNA. found that the amounts of A, T, C, and G varied from species to species. - observed the amounts of the 4 nitrogenous bases found in different samples of DNA. paper chromatography was used to separate the substances in the DNA and UV spectrophotometry was used to count the amount of each base in each sample. - discovered part of the structure of DNA, allowed Watson and Crick to make their final discovery.

Answer 33

- cystic fibrosis - sickle cell anaemia (however, anaemia is not inherited) - colour blindness

Answer 34

the result of a gene mutation. not always negative, but can affect your vision/quality of life.

Answer 35

a change to a DNA base sequence (e.g. a C changes to a G). - these mutations happen spontaneously all the time, especially when DNA is being duplicated for cell division

Answer 36

- carcinogens (harmful chemicals, e.g. in cigarette smoke) - certain types of radiation (e.g. x-rays, gamma rays)

Answer 37

e.g. ATG GGA ... , and this creates a certain protein shape. this could change to: ATG GGG, and it could still encode the same protein shape, by not changing the amino acid sequence. this is because different base triplets can sometimes encode for the same amino acid, or it may only affect a protein very slightly (look slightly different, but work in the same way) this mutation has no effect on the protein's shape/function (phenotype). this is the case for most mutations.

Answer 38

- the protein has a different amino acid sequence, and this has altered its shape. - this can have a dramatic effect on its function. - e.g. the active site on an enzyme may have changed shape, so it can no longer attach to the substrate. it can't form an enzyme-substrate complex, so can no longer catalyse a reaction - e.g. if it changes the shape of a structural protein (e.g. collagen), it may lose its strength

Answer 39

- very rarely leads to a changed, new phenotype - sometimes, a new phenotype can be beneficial if the environment changes, and this can lead to a rapid change in the species, through reproduction - e.g. resistance to a disease

Answer 40

non-coding DNA

Answer 41

- these regions switch genes on and off. - tell genes when to produce proteins. - e.g. the gene coding for haemoglobin in a nerve cell may be switched off, as there's no need for it, so it's not expressed - mutations in these non-coding regions can affect how genes are switched on or off. e.g. a gene may be turned on that is supposed to be turned off. - as a result, the cell would produce a protein that it is not meant to have at that time. this could have a significant effect on a cell (e.g. uncontrolled mitosis, leading to cancer).

Answer 42

a group of conditions that can be passed on in certain alleles, and so can be inherited from a person's parents

Answer 43

- disorder of the cell membranes, resulting in a thick sticky mucus being released in different parts of the body, e.g. airways of the lungs, pancreas - controlled by a single gene. - the allele for normal cell membranes is dominant (C), and the allele for defective cell membranes is recessive (c). therefore, in order to have cystic fibrosis, the person must have 2 copies of the defective allele. - a person with the Cc genotype does not have cystic fibrosis, but instead a carrier of the disorder.

Answer 44

- people who have extra fingers or toes, but doesn't usually cause any other problems - caused by a dominant allele (only need one copy of the polydactyly allele to have the disorder) - not possible to be a carrier of this disorder, or of any dominant allele

Answer 45

- embryos tested to see if they have the alleles for inherited disorders - alleles without the defective alleles are implanted into the woman, and develop into healthy offspring ------------------------------------------------------------ - reduces the overall amount of suffering (fewer people will have health problems) - saves money (treating genetic disorders is expensive)

Answer 46

- expensive. people believe the money should be spent elsewhere in the health service - often a large number of embryos are created, but only a small number are implanted. that means some healthy embryos are destroyed, and some think that's unethical - in the future we may be able to screen embryos to produce offspring with desirable features (e.g. taller/more intelligent offspring). some find this unethical, and is illegal in the UK - implies that people with genetic disorders are less desirable, increasing prejudice

Answer 47

the treatment of an inherited disorder by giving the patient a healthy copy of the faulty gene. - at the moment, however, this is still experimental, and we don't know the potential effects of modifying gene on other genes

Answer 48

giving a person a healthy version of a gene, and hoping it will fix the problem - however, the faulty gene would be in all of the cells of the body, so we'd need to transfer this new gene to every cell, which is difficult. we would then transfer the gene at an early stage of development, as then as the person develops, the healthy gene will be passed onto all cells

Answer 49

- most common life-threatening disease in the UK, affects 1 in 2500 people, affects around 100,000 people globally - usually develops in early childhood - build-up of sticky mucus, affects the lungs and digestion - can cause recurring chest infections (due to bacteria being stuck in the chest mucus); wheezing, coughing, shortness of breath; difficulty putting on weight. can develop other conditions such as diabetes, weakened bones (osteoporosis), male infertility (affects sperm ducts/testes), diarrhoea. - this is because it clogs the pancreatic duct and limits digestive enzyme secretion, limiting the absorption of fats, proteins, and vitamins.

Answer 50

the sweat test. checks for high levels of chloride in the sweat - people with CF have higher amounts of sodium and chloride in their sweat.

Answer 51

- antibiotics to prevent/treat chest infections - medicines to thin the mucus and make it easier to cough it up - medicines to widen the airways and reduce inflammation - medicines to help digestion - physiotherapy loosens the mucus - enzyme and vitamin tablets help keep the levels up - oxygen gas improves breathing

Answer 52

CHORIONIC VILLUS SAMPLING (CVS): sampling of embryonic cells between 10-12 weeks old. takes a sample of tissue from the developing placenta, from the chorionic villi, and test these cells. it's a diagnostic test (gives a yes/no answer), but only tests for chromosome disorders such as down syndrome. AMNIOCENTIS: (sampling of embryonic cells between 15-16 weeks). take fluid from around the foetus, this fluid contains the cells used for screening. this causes a small chance of miscarriage, but lab errors are rare.

Answer 53

only shows phenotypes and not genotypes

Answer 54

- humans contain 23 pairs of chromosomes in normal body cells - 22 of the chromosome pairs contain the genes which determine inherited characteristics only - one of the chromosomes contain the genes that determine sex

Answer 55

males = XY females = XX - 50% chance of either sex

Answer 56

the differences in the characteristics (phenotypes) of individuals in a population - most of our characteristics are formed by the interaction of our genes with our environment

Answer 57

mutations. if the protein is different, due to a change in an organism's DNA code, the phenotype may also change - most of the time, this results in a negative change, but it can sometimes be beneficial (e.g. resistance to a disease, improved abilities) - these organisms with beneficial mutations are more likely to survive and reproduce, passing on their genes to the next generation SURVIVAL OF THE FITTEST/NATURAL SELECTION (the fittest individuals are being selected to survive)

Answer 58

the alleles that individuals have inherited - includes hair colour, eye colour

Answer 59

- the colour of some flowers depends on the pH of the soil - language in humans

Answer 60

- height in humans - some people have alleles that make them likely to grow taller - however, their diet must include enough calcium to allow their bones to fully develop

Answer 61

- scientists believe that life first developed on Earth over 3 billion years ago - these first life forms were simple (e.g. single cells) - all living things have evolved from this simple life form

Answer 62

- every rabbit will have a slightly different combination of alleles that it inherited from its parents - some rabbits will have alleles for thicker fur, better eyesight, or better hearing

Answer 63

- rabbits which have inherited the alleles for thicker fur are more likely to survive the colder temperatures than those with thinner fur - the rabbits with thicker fur can survive the cold and then reproduce - their offspring could inherit the alleles for thicker fur, and these are more likely to survive the cold and reproduce - over many generations, this allele will become more common among the population of rabbits

Answer 64

- a predator moves into the area, e.g. a fox - the rabbits with alleles for better eyesight/hearing have an advantage - these rabbits are more likely to detect the fox as it approaches, so they're more likely to survive and reproduce - these beneficial alleles will be passed onto the offspring, and over several generations, these alleles will be widespread

Answer 65

the change in the inherited characteristics of a population over time through a process of natural selection - this could lead to a change in the whole species, or even a development of an entirely new species

Answer 66

simple life forms that first developed over 3 billion years ago

Answer 67

two populations of one species can become so different in phenotype that they can no longer interbreed to produce fertile offspring

Answer 68

- domestic dogs have been bred to have a more gentle nature - food crops (e.g. wheat) have been bred to be resistant to disease - animals (e.g. cows) have been bred to produce more meat/milk - plants have been bred to produce large/unusual flowers

Answer 69

the best plants or animals in a population are bred together in the hope of getting even better offspring

Answer 70

1. take a mixed population of cows. select the largest male and female (take the organisms with the desired characteristics in the population) 2. breed these together. sexual reproduction produces variation in the offspring, so usually they'd be a mixture of larger and smaller animals 3. constantly selecting the largest male and female offspring to breed together means eventually all offspring will be large

Answer 71

- reduces the gene pool of a population (the collection of different alleles in a population). the best individuals are usually closely related as they both have the good genes, so breeding them together can lead to inbreeding - inbreeding can cause some breeds to be prone to disease or inherited defects - e.g. inbred dog breeds can develop inherited disorders such as joint problems, heart disease, or epilepsy - a small gene pool also leads to less variation within a population, meaning an incoming pathogen, for example, will affect all of them, and possibly wipe out the entire population

Answer 72

genes from one organism (e.g. humans) are cut out an transferred to the cells of a different organism (e.g. bacteria) - the genome of the bacteria is modified and now contains a human gene - the genes from an organism with a desirable characteristic are taken and transferred to another organism, so this organism has the same trait. this organism is genetically modified (GM) - can do this intraspecies or interspecies

Answer 73

- insulin = hormone involved in blood glucose regulation in humans - people with type 1 diabetes cannot make their own insulin, so must inject themselves with it regularly - bacteria have been genetically modified to contain the human insulin gene, and these now produce human insulin. this can then be purified and used for type 1 diabetes

Answer 74

- can transfer genes into plants to produce genetically modified (GM) crops - these generally produce a greater yield, or can be disease/insect resistant, or can produce bigger/better fruits (more food for less money, which is important in developing countries, where famine is common) - some GM crops are resistant to herbicides, meaning farmers can spray their fields to kill weeds without killing the crops too - crops can be modified to contain nutrients, e.g. golden rice protects people from blindness, due to beta carotene

Answer 75

- could be unsafe. e.g. harmful to insects or wild flowers - some people feel we need to do more research on the health effects of eating GM crops - the plants could make their way into the wild, introduce competition and change the entire ecosystem. however, this is unlikely as the plants have been modified to survive in the farmer's field, not in the wild

Answer 76

1. identify the gene we want to transfer (e.g. human gene, animal/plant gene) 2. use enzymes to isolate this gene 3. transfer the gene into a small circle of DNA called a plasmid (from a bacteria). we could also use a virus 4. the plasmid/virus will transfer the DNA from one organism to the cells of the target organism, therefore they're vectors. the organism's cells will take up the vector and the contained useful genes and start producing a protein that the gene codes for

Answer 77

- always transfer the gene at an early stage in an organism's development - e.g. if we were transferring the gene into an animal, we would do it during the early embryo stage - this would ensure that all of the cells receive the transferred gene, so the organism develops with the characteristic we want

Answer 78

- modified sheep to produce drugs in their milk that we can extract and use to treat diseases - modified bacteria to produce the hormone insulin that we can harvest and use to treat diabetes - modifying crops to increase the size and quality of their fruit, to become resistant to diseases, insects, and herbicides, etc.

Answer 79

as the clone is genetically identical to the original plant (mitosis), we know exactly what its characteristics will be (e.g. the colour of the flowers)

Answer 80

- gardeners have been using this method for a long time - a small piece of the plant is removed (e.g. growing shoot/branch) and the end is dipped in rooting powder and then planted - rooting powder contains plant hormones and encourages it to develop roots - produces a genetically identical clone of the original plant

Answer 81

1. find a plant with desirable characteristics to clone 2. take very small pieces of plant tissue (explants) from the tips of stems, using scalpel/razor/scissors/knife 3. sterilise the explants to remove any microorganisms 4. place the explants in a nutrient medium (e.g. agar, containing growth hormones) and let them grow into small masses of cells called calluses 5. transfer (with tweezers/forceps) the calluses to the soil where they can grow into plantlets (baby plants) 6. the plantlets can be transferred to their own pots to develop into genetically identical adult plants --------------------------------------------------------------- - conditions must be sterile as we don't want any microorganisms such as bacteria or fungi to enter

Answer 82

- nitrates for amino acids/proteins - glucose/sucrose for energy/respiration - magnesium for chloroplasts/chlorophyll

Answer 83

- sterile/aseptic conditions - temperature - light - humidity - growth hormones

Answer 84

- cuttings is quicker and cheaper - cuttings requires less technical expertise/equipment - don't have to worry about sterilisation so much for cuttings

Answer 85

- useful in commercial plant nurseries - allows growers to produce thousands of genetically identical plants quickly and cheaply - gardeners can be certain the plants will have the characteristics they want - tissue culture can also be used to preserve a rare species of plants

Answer 86

- start with a sperm and egg cell from horses with the desired characteristics - fertilise the egg, and allow it to develop into an early stage embryo. however, the cells in the embryo must not have started to specialise - use a glass rod to split this embryo into two - transplant the embryo into two host mothers. the embryos will grow and develop, and when the animals are born, we will have two genetically identical offspring (clones)

Answer 87

as we start with a sperm and an egg (sexual reproduction, therefore variation), we cannot be certain that the offspring will have the characteristics we want - therefore, use adult cell cloning, as we can be certain of the characteristics the clone will have

Answer 88

1. remove a cell from the animal we want to clone (e.g. skin cell) 2. remove the diploid nucleus from the cell, containing the animal's genetic information 3. take an unfertilised egg cell from the same species, e.g. any female sheep 4. remove the nucleus from the unfertilised egg, so it now contains no genetic material at all 5. insert the nucleus from the original adult body cell into the empty egg cell 6. stimulate the egg cell by giving it an electric shock, causing it to act like a zygote and divide to form an embryo 7. when the embryo has developed, it's inserted into an adult female (surrogate mother) to continue its development 8. the clone is then birthed

Answer 89

- all offspring are identical (no variation) - quicker - more offspring are produced - no need for natural mating/two parents

Answer 90

the nucleus

Answer 91

- took part in a global expedition in the 1800s - collected a vast number of different plants and animals, he was fascinated by the variety - spent many years studying geology and fossils - many species of animals and plants alive today are similar to extinct species - said that natural selection is the driving force behind the gradual development of species over time

Answer 92

- using genetic engineering, scientists can place human genes into the DNA of other organisms, e.g. cows, sheep, goats - once an organism has DNA from another species, it's 'transgenic' - we can genetically engineer cows, sheep, and goats to produce helpful human proteins in their milk. if a cow had the human insulin gene, it would produce the human insulin protein, which can be extracted and used - instead of genetically engineering organisms each time, we can often clone the transgenic organisms

Answer 93

older layers of rock contained fossils of less complex organisms, while more recent layers show more complex organisms

Answer 94

1. within a species, there is a wide range of genetic variation for any characteristic/trait 2. individuals with characteristics most suited to the environment are more likely to survive to breed successfully 3. the characteristics that have enabled these individuals to survive are then passed onto the next generation

Answer 95

- published his findings in 'On the Origin of Species' - extremely controversial theory, only gradually accepted - at the time, a lot of people strongly believed that God made all the animals and plants on Earth, and Darwin's theory challenged this idea - many scientists believed he didn't have enough evidence to back his theory up - genetics and DNA wasn't understood until 50 years after Darwin's theories were published --------------------------------------------------------------- - Darwin's theory has now been proven multiple times. we can see antibiotic resistance in bacteria, and looked at fossil records

Answer 96

suggested that when a characteristic is regularly used in an organism's lifetime, it becomes more developed. this strengthened characteristic is then passed onto the offspring - e.g. giraffes started with shorter necks adapted to lower vegetation. they stretched their necks to reach higher branches for food, resulting in longer necks during their lifetime. this acquired longer neck was passed onto offspring, and onto successive generations

Answer 97

- we now know that in the vast majority of cases, changes that occur in an organism's lifetime cannot be passed onto offspring, as they do not affect the DNA sequence of an organism - Lamarck's theory is therefore incorrect, and scientists accept Darwin's theory as how species change

Answer 98

1. some giraffes had longer necks than others, due to variation within the species 2. giraffes with longer necks were better adapted to their environment, so could eat the leaves from taller trees 3. giraffes with longer necks had a higher chance of surviving and reproducing, so passed on the traits of their long necks to their offspring 4. over many generations, this produced modern giraffes with long necks

Answer 99

- travelled globally looking at different animals and plants - interested in the warning colouration in animals, and how they'd evolved (e.g. bright red frogs could warn predators that it's poisonous) - independently proposed his own theory of evolution through natural selection, and also came up with the idea of speciation - him and Darwin realised they had the same theory, so they jointly published their findings

Answer 100

the evolutionary process by which populations evolve to form distinct, new species that can no longer interbreed and create fertile offspring

Answer 101

a combination of both: - isolation (a physical barrier, e.g. river/mountain range, separates 2 different populations of the same species) - natural selection

Answer 102

a group of genetically similar organisms that are able to interbreed and produce fertile offspring

Answer 103

1. two populations become isolated (by a geographical barrier, e.g. river/mountain) 2. these populations have different gene pools/have developed different mutations 3. each population was exposed to different environmental conditions (e.g. weather, water levels) 4. natural selection occurs in the 2 populations, favouring the alleles that best suit each environment 5. the two populations become genetically different and can no longer interbreed to produce fertile offspring

Answer 104

- carried out many experiments on pea plants, and looked at their characteristics (shape/colour of pod, colour of flowers, height) - from this, he realised that characteristics aren't 'blended' during inheritance. e.g. the shape of a pea pod has no effect on the colour of the flower. - Mendel said that characteristics are determined by inherited units (genes), which don't change when passed onto descendants - also showed that some characteristics can be masked and then reappear in later generations - recessive alleles

Answer 105

1. took a green pea pod and a yellow pea pod. crossed the two plants together. the offspring were all yellow pea plants 2. took 2 of these yellow offspring pea plants. this time, 1 in every 4 pea plants were green (the yellow plants still had the hereditary units for green pods, they just weren't being expressed, as they were recessive) - concluded that there must be inherited units passed on from generation to generation, and that they can either be recessive or dominant - Mendel also did these experiments with other traits, e.g. height of plant, colour of flowers, but each time he found the same pattern, suggesting all of these characteristics are passed down in this dominant/recessive way

Answer 106

- published his research in a scientific paper - many scientists held onto the idea that characteristics are blended, and forgot about his work, despite it being a major discovery --------------------------------------------------------------- - in the late 1800s, scientists looked at how chromosomes behave during cell division, and rediscovered Mendel's work on cell genetics - by the early 1900s, they realised that Mendel's units (genes) behaved in a similar way to chromosomes. they realised that genes must be located on chromosomes - in the mid 1900s, scientists determined the structure of DNA and how genes function - later, in 2003, we were able to figure out the entire human genome

Answer 107

the remains of organisms from millions of years ago which are found in rocks - they're important as most of the organisms that ever lived are now extinct, so the only way to learn about them is by looking at what they left behind - by studying organisms, evidence is provided for evolution, as we can see the small, incremental changes that took place over millions of years

Answer 108

1. parts of organisms that haven't decayed, e.g. when the conditions needed for decay are absent (low temperature, lack of oxygen/water in amber,tar pits, glaciers - too cold - , peat bogs - too acidic - for example) 2. if parts of the organism (e.g. shells, teeth, bones) are slowly replaced by minerals during the decay process, forming rock-like substance in the same shape and size as the original structures 3. could be the preserved traces/casts/impressions of organisms in soft material such as clay. as the clay hardens, we're left with a gap the same size/shape as the organism left (e.g. footprints, burrows, plant root spaces)

Answer 109

- many of the earliest forms of life were soft-bodied organisms (no shell/skeleton), which don't form fossils as they decayed quickly - any fossils that did form have been destroyed by changes to the rock in the Earth's crust (eartquakes, volcanoes, movement of tectonic plates) - there are therefore very few fossils of the early forms of life, and large gaps in time with no fossils, so scientists cannot be certain on how life began

Answer 110

that a huge number of species have become extinct

Answer 111

- catastrophic event (e.g. asteroid) - environmental changes too quickly (e.g. changing weather patterns) - new disease/predator - new, more successful species evolves and competes with the pre-existing species, e.g for water

Answer 112

millions of years

Answer 113

under ideal conditions, can reproduce every twenty minutes - due to this, they can evolve rapidly

Answer 114

- in the 1940s, doctors began to treat bacterial diseases using antibiotics such as penicillin - antibiotics kill bacteria - they're now widely used in medicine - also used in farming, to prevent animals from developing bacterial diseases

Answer 115

in the last few years, certain strains of bacteria are no longer killed by antibiotics. these bacteria have evolved and are now antibiotic resistant - a common antibiotic resistant strain is MRSA

Answer 116

1. it's possible that a mutation (as they happen so often) could make a bacterium resistant to antibiotics 2. if we use an antibiotic on a bacteria population, all of the bacteria are killed apart from the antibiotic resistant bacterium 3. this survives and reproduces very quickly, without competition, and the population of this resistant strain rises, forming a colony 4. as the antibiotic isn't effective anymore, the person is still affected, so can pass on this resistant bacteria to others. if they then go and get the same antibiotic, it won't work

Answer 117

bacteria that is resistant to lots of different types of antibiotics

Answer 118

- a superbug - relatively common, as its resistance makes it so hard to kill

Answer 119

1. doctors shouldn't prescribe antibiotics inappropriately, e.g. no point in using an antibiotic to treat a virus, and don't prescribe them for mild bacterial infections that will clear quickly anyway 2. patients should make certain to complete their course of antibiotics, ensuring all of the bacteria are killed and none can survive to mutate and form resistant strains 3. restrict the use of antibiotics in farming, which is usually just so the livestock don't get ill in the first place, or so they are healthier

Answer 120

- takes a long time - extremely expensive - as new antibiotic resistant bacteria emerge all the time, it's unlikely that we'll be able to keep up

Answer 121

- in the 1700s, he began to classify species into different categories based on their (bone) structure and characteristics - divided all living organisms into 2 kingdoms: animal and plant - then divided each kingdom into a number of smaller categories

Answer 122

- different countries have different names for animals - these names don't tell us much about how the animals are related

Answer 123

- kingdom (e.g. plant/animal) - phylum - class - order - family - genus - species

Answer 124

- binomial naming system, mainly latin - named from their genus and species - naming organisms just by the species name isn't enough, as multiple species could have the same name

Answer 125

- each species has a unique name - it lets scientists discuss individual species

Answer 126

- based on visible characteristics - however, there have been major advances since then (e.g. we can now use microscopes to analyse internal structures, and can analyse an organisms biochemistry, e.g. its DNA and look for similarities with other species)

Answer 127

- developed by Carl Woese, compared the biochemistry (RNA sequences) of different organisms, and found that some species are less related than we thought --------------------------------------------------------------- - these domains are placed above kingdoms ARCHAE/PRIMITIVE BACTERIA: different type of prokaryotic cell that lives in extreme conditions e.g. hot springs TRUE BACTERIA: tiny, single-celled prokaryotic organisms EUKARYOTA: animals, plants, fungi, protists (amoeba)

Answer 128

- show the evolutionary relationships between different species/groups by linking common ancestors. the more recent the common ancestor, the more closely related the species are - scientists, to make one, can use classification data on living organisms (e.g. their structure DNA) - for extinct organisms, scientists must use fossils. this is a problem, as the fossil records for many species are incomplete