inheritance, variation and evolution

Question 1

what is DNA

Answer 1

• stands for deoxyribonucleic acid
• its the chemical that all of the generic material in a cell is made from
• DNA is a polymer made up of two strands coiled together in the shape of a double helix

Question 2

what is a gene

Answer 2

a gene is a small section of DNA found on a chromosome. each gene codes for a particular sequence of amino acids which are put together to make a specific protein

Question 3

how many amino acids are used in a gene

Answer 3

20 amino acids are used, but they make up thousands of different proteins

Question 4

what is a genome

Answer 4

the entire set of genetic material in an organism

Question 5

why is understanding the human genome important for science and medicine

Answer 5

• it allows scientists to identify genes in the genome that are linked to different types of diseases
• help us understand inherited diseases better and develop effective treatments for them
• to trace the migration of certain population of people around the world

Question 6

what is sexual reproduction

Answer 6

sexual reproduction is where genetic information from two organisms is combined to produce offspring which are genetically identical to either parent. it involves the fusion of male and female gametes. because there are two parents, the offspring contains a mixture of their parents’ genes

Question 7

what is the process by which the mother and father produce gametes

Answer 7

meiosis

Question 8

how many chromosomes does each gamete contain

Answer 8

23

Question 9

how is variation produced in the offspring

Answer 9

it inherits features from both parents as it receives a mixture of genetic information from its mother and father which produces variation

Question 10

how is asexual reproduction different to sexual reproduction

Answer 10

in asexual reproduction there is only one parent. there is no fusion of gamers, no mixing of chromosomes and no genetic variation between parent and offspring. the offspring is genetically identical to the parent - they’re clones

Question 11

what process happens in asexual reproduction to make a new cell

Answer 11

mitosis

Question 12

how many copies of each chromosome does a gamete have

Answer 12

one

Question 13

how does meiosis produce cells with half the normal number of chromosomes

Answer 13

1) before the cell starts to divide, or duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm. after replication, the chromosomes arrange themselves into pairs
2) in the first division in meiosis the chromosome pairs line up in the centre of the cell
3) the pairs are then pulled apart so each new cell only has one copy of each chromosome. some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell
4) in the second division, the chromosomes line up again in the centre of the cell. the arms of the chromosomes are pulled apart
5) you get four gametes, each with only a single set of chromosomes in it. each of the gametes is genetically different from the others because the chromosomes all get shuffled up during meiosis and each gamers only gets half of them, at random

Question 14

how is a whole organism made after the fertilisation of gametes

Answer 14

after two gametes have fused together during fertilisation, the resulting new cell divides by mitosis to make a copy of itself. mitosis repeats mant times to produce lots of new cells in an embryo. as the embryo develops these cells then start to differentiate into the different types of specialised cell that make up a whole organism

Question 15

what combination of chromosomes do males have

Answer 15

XY

Question 16

what combination of chromosomes do females have

Answer 16

XX

Question 17

what happens when making sperm

Answer 17

X and Y chromosomes are drawn apart in the first division of meiosis. there’s a 50% chance each sperm cell gets an X-chromosome and a 50% chance it gets a Y-chromosome.

Question 18

what is an allele

Answer 18

the different versions that genes exist in

Question 19

how many alleles of every gene do you have

Answer 19

2

Question 20

what is homozygous

Answer 20

when an organism has two alleles for a particular gene that are the same

Question 21

what is heterozygous

Answer 21

when an organism has two alleles for a particular gene that are different

Question 22

what are the two types of alleles in a heterozygous gene

Answer 22

dominant & recessive

Question 23

for an organism to display a recessive characteristic, how many of its alleles should be recessive

Answer 23

as the dominant allele overrules the recessive one, both of the alleles must be recessive

Question 24

what is your genotype

Answer 24

the combination of alleles you have

Question 25

what is your phenotype

Answer 25

when your alleles work at a molecular level to determine what characteristics you have (the characteristics it displays)

Question 26

what is cystic fibrosis

Answer 26

a genetic disorder of the cell membranes. it results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas

Question 27

what type of allele causes cystic fibrosis

Answer 27

recessive allele

Question 28

what is the chance of a child being born with cystic fibrosis if both their parents are carriers

Answer 28

1 in 4 chance / 25%

Question 29

what is polydactyl

Answer 29

a genetic disorder where a baby’s born with extra fingers or toes

Question 30

what type of allele causes polydactyl

Answer 30

a dominant allele

Question 31

what is the chance of a child being born with polydactyl if one parent was a single dominant allele for the gene that controls it

Answer 31

50% chance

Question 32

how can genetic disorders be detected and removed in IVF

Answer 32

during IVF, embryos are fertilised in a lab and then implanted into the women’s womb. before being implanted, it’s possible to remove a cell from each embryo and analyse its genes. it’s also possible to get DNA from an embryo in the womb and test that for disorders. this is known as embryo screening

Question 33

what are the ethical arguments for & against embryo screening

Answer 33

for: - it will help to stop people suffering - treating disorders costs the government (and taxpayers) a lot of money - there are laws to stop it going too far. at the moment parents cannot even select the sex of their baby (unless it’s for health reasons) against: - it implies that people with genetic problems are ‘undesirable’ - this could increase prejudice - there may come a point where everyone wants to screen their embryos so they can pick the most ‘desirable’ one, e.g. wanting a blue-eyed, blond-haired, intelligent boy - screening is expensive

Question 34

what is variation

Answer 34

differences between organisms of the same species

Question 35

what a mutation

Answer 35

a rare, random change in an organism’s DNA that can be inherited

Question 36

what is a genetic variant

Answer 36

a different form of a been which can be caused by mutations

Question 37

do mutations affect an organism’s phenotype

Answer 37

most genetic variants have very little or no effect on the protein the gene codes for. some will change it to such a small extent that its function is unaffected. this means that most mutations have no effect in an organism’s phenotype

Question 38

how does cystic fibrosis affect a person’s phenotype

Answer 38

it’s caused by a mutation that has a huge effect on phenotype. the gene codes for a protein that controls the movement of salt and water in and out of cells. however, the protein produced by the mutated gene doesn’t work properly. this leads to excess mucus production in the lungs and digestive system, which can make it difficult to breathe and to digest food.

Question 39

what is the theory of evolution

Answer 39

all of today’s species have evolved form simple life forms that first started to develops over three billion years ago

Question 40

who created the theory of evolution by natural selection

Answer 40

charles darwin

Question 41

explain how beneficial characteristics can become more common in a population overtime

Answer 41

organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive: ‘survival of the fittest’. the successful organisms that survive are more likely to reproduce and pass on the genes for the characteristics that made them successful to their offspring. the organisms rhay are less well adapted would be less likely to survive and reproduce, so they are less likely to pass om their genes to the next generation. overtime, beneficial characteristics become more common in the population and the species changes - it evolves

Question 42

what evidence is there to support the theory of natural selection

Answer 42

- discovery of genetics provided an explanation of how organisms born with beneficial characteristics can pass them on and showed that it is genetic variants that give rise to phenotypes that are suited to the environment - looking at fossils of different ages allows you to see how changes in organisms developed slowly over time - discovery of how bacteria are able to evolve to become resistant to antibiotics

Question 43

what is speciation

Answer 43

the phenotype of organisms can change so much because of natural selection that a completely new species is formed. speciation happens when populations of the same species change enough to become reproductively isolated - they can’t interbreed to produce fertile offspring

Question 44

what is extinction

Answer 44

when no individuals of a species remain

Question 45

reasons for extinction

Answer 45

- environment changes too quickly - a new predator kills them all - a new disease kills them all - they can’t compete with another (new) species for food - a catastrophic event happens that kills tram all (e.g. volcanic eruption)

Question 46

what is selective breeding

Answer 46

when humans artificially select the plants or animals that are going to breed so that’s the genes for particular characteristics remains in the population

Question 47

give examples of features that organisms are selectively bred to develop

Answer 47

- animals that produce more meat or milk - crops with disease resistance - dogs with a good, gentle temperament - decorative plants with big or unusual flowers

Question 48

explain the process of selective breeding

Answer 48

1) from your existing stock, select the ones which have the characteristics you’re after 2) breed them with each other 3) select the best of the offspring. and breed them together 4) continue this process over several generations, and the desirable trait gets stronger & stronger. eventually all the offspring will have the characterisric

Question 49

how might farmers use selective breeding

Answer 49

i’m agriculture, selective breeding can be used to improve yields. e.g. to improve meat yields, a farmer could breed together the cows and bulls with the best characteristics for producing meat, e.g. large size. after doing this for several generations the farmers would get cows with a very high meat yield

Question 50

what is the problem with selective breeding

Answer 50

it reduces the gene pool (the number of different alleles in a population). this is because the farmer keeps breeding from the “best” animals or plants which are all closely related. this is known as inbreeding.

Question 51

what’s the problem with inbreeding

Answer 51

inbreeding can cause health problems because there’s more of the organisms inheriting harmful genetic defects when the gene pool is limited. there can also be serious problems if a new disease appears. because there is not much variation in the population, all the stock are closely related to each other, so if one of them is going to be killed by a new disease. the others are likely to succumb to it

Question 52

what is genetic engineering

Answer 52

genetic engineering transfers a gene responsible for a desirable characteristic from one organism’s genome to another organims, so that if also has the desirable characteristic

Question 53

explain the process of genetic engineering

Answer 53

1) a useful gene is isolated (cut) from one organism’s genome using enzymes and is inserted into a vector 2) the vector is usually a virus or a bacterial plasmid, depending on the type of organism that the gene is being transferred to 3) when the vector is introduced to the target organism, the useful gene is inserted into its cell(s)

Question 54

examples of when scientists have used genetic engineering

Answer 54

- bacteria have been genetically modified to produce human insulin that can be used to treat diabetes - genetically modified (GM) crops have had their genes modified, e.g. to improve size/quality of their fruit, make them resistant to disease/insects/herbicides - sheep have been genetically engineered to produce substances, like drugs, in their milk that can be used to treat human diseases - scientists are researching genetic modification treatments for inherited diseases caused by faulty genes, e.g. by inserting working genes into people with the disease (gene therapy)

Question 55

why is genetic engineering controversial

Answer 55

- genetic engineering has the potential for solving many of our problems (e.g. treating diseases, more efficient food production etc) - some may worry about the long-term effects of genetic engineering - changing an organism’s gene might accidentally create unplanned problems which could get passed on to the future generations

Question 56

pros & cons of GM crops

Answer 56

pros: - characteristics chosen for GM crops can increase the yield, making more food - GM crops could be engineered to contain the nutrients that people living in developing nations often lack - GM crops have already been grown in some places without any problems cons: - some say GM crops will affect the number of wild flowers (and so the population of insects) that live in & around the crops - reducing farmland biodiversity - not everyone agreed GM crops are safe - we might not understand the effects of eating them on human health - transplanted genes may get out into the natural environment

Question 57

what are fossils

Answer 57

fossils are the remains of organisms from many thousands of years ago, which are found in rocks

Question 58

give 3 ways fossils can be formed

Answer 58

• from gradual replacement by minerals - things like teeth, shells, bones which don’t decay easily can last a long time when buried. they’re eventually replaced by minerals as they decay forming a rock-like substance shaped like the original hard part - the surrounding sediments also turn rock, but the fossil stays distinct inside the rock and eventually someone digs it up • from casts and impressions - organism is buried in a soft material like clay. the clay later hardens around it and the organism decays, leaving a canst of itself - an animal’s burrow or a plant’s roots can be preserved as casts - footprints can also be pressed into these materials when soft, leaving an impression when it hardens • from preservation in places where no decay happens - in amber and tar pits, there’s no oxygen or moisture so decay microbes can’t survive - in glaciers it’s too cold for the decay microbes to work - peat bogs are too acidic for decay of microbes

Question 59

what leads to the formation of antibiotic-resistant strains of bacteria

Answer 59

bacteria can sometimes develop random mutations in their DNA. these can lead to changes in the bacteria’s characteristics e.g. being less affected by a particular antibiotic. this can lead to antibiotic-resistant strains forming as the gene for antibiotic resistance becomes more common in the population

Question 60

why are antibiotic-resistant strains a problem for people who become infected with these bacteria

Answer 60

because they aren’t immune to the new strain and there is no effective treatment. this means that the infection easily spreads between people. sometimes drug companies can come up with a new antibiotic that’s effective, but ‘superbugs’ that are resistant to most known antibiotics are becoming more common

Question 61

why is it important that you take all the antibiotics a doctor prescribes for you

Answer 61

taking the full course makes sure that all the bacteria are destroyed, which means that there are none left to mutate and develop antibiotic-resistant strains

Question 62

who created the system which organisms are classified into

Answer 62

carl linnaeus

Question 63

in the linnaean system, what are the kingdoms subdivided into

Answer 63

phylum, class, order, family, genus, species

Question 64

who proposed the ‘three-domain system’ of classification in 1990

Answer 64

carl woese

Question 65

what are the three domains that organisms are split into

Answer 65

archaea bacteria eukaryota

Question 66

what is archaea

Answer 66

organisms in this domain are primitive bacteria. they’re often found in extreme places such as hot springs and salt lakes

Question 67

what is bacteria domain

Answer 67

this domain contains true bacteria. although they often look similar to archaea, there are lots of biochemical differences between rhem

Question 68

what is the eukaryota domain

Answer 68

this domain includes a broad range of organisms including fungi, plants, animals, and protists

Question 69

how are organisms named according to the binomial system

Answer 69

- every organism is given its own two-part latin name - the first part of refers to the genus that the organism belongs to. this gives you information on the organism’s ancestry - the second part refers to the species

Question 70

what do evolutionary trees show

Answer 70

how scientists think different species are related to each other. they show common ancestors and relationships between species. (the more recent the common ancestor, the more closely related the two species - and the more characteristics they share)