Biology - Inheritance, variation and evolution Flashcards
1
Q
How many strands is the helix structure of DNA made up of
A
2
2
Q
The DNA in typical human cells is found in tight coils known as
A
chromosomes
3
Q
How many chromosomes are there in a typical human cell
A
46 - the human has 23 pairs of chromosmes
4
Q
The chromosomes in the 23rd pair are known as
A
Sex chromosomes
5
Q
Do women have XX or XY chromosomes
A
XX
5
Q
What is a gene
A
A small section of DNA that codes for a specific protein
6
Q
What does the term genome mean
A
The entire set of genetic material in an organism
7
Q
What are alleles
A
Different versions of a particular gene
8
Q
What does homozygous mean
A
Both alleles are the same
9
Q
Dominant allele meaning
A
It will be expressed over the recessive allele
10
Q
Genotype meaning
A
Two alleles present for a particular gene
11
Q
Phenotype meaning
A
The characteristics an organism has as a result of their genotype
12
Q
What are the monomers of DNA
A
Nucleotides
13
Q
What are the 4 types of bases in DNA
A
Adenine
Thymine
Cytosine
Guanine
14
Q
What are the complementary baes
A
A always has to pair with T
C always has to pair with G
15
Q
What codes for a specific amino acid
A
Each set of three bases (triplets)
16
Q
Main functions of proteins
A
Speed up the rate of chemical reactions - enzymes
Carry messages around the body (hormones)
17
Q
What is a section if a DNA that codes for a protein called
A
gene
17
Q
What is transcription in protiensynthesis
A
The copying of a single gene of DNA, to mRNA
18
Q
Where does transcription take place
A
Nucleus
19
Q
Why dies a gene of DNA have to be copied to mRNA
A
DNA is too large to leave in the nucleus
20
Q
Difference between mRNA and DNA
A
mRNA is shorter than DNA
mRNA is single stranded, but DNA is double stranded
21
Q
Where does the mRNA go once it leaves the nucleus and enters the cytoplasm
A
Ribosome
22
Q
What is translation in terms of protein synthesis
A
The combination of amino acids to form a polypeptide
23
How many bases are needed to code for one amino acid
3
24
What is the function of a ribosome?
To assemble proteins from amino acids
25
What is a chain of amino acid called
Polypeptide
26
What is a mutation?
A change in the base sequence of an organisms DNA
27
What is a triplet/ codon?
A set of 3 bases which codes for one amino acid
28
What happens if there ia a mutation to one of the bases in DNA
It can change the amino acid that the codon codes for
29
What is the most likely result of a genetic mutation
No significant change to the organism
30
Most mutations occur in
non-coding DNA
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What does non-coding DNA do
Controls the expression of coding DNA
32
What does it mean for a gene to be expressed?
It's turned on, so the proteins it codes for will be produced
33
What happens in a substitution mutation
One base in a sequence is replaced with a different base
34
Describe how a change of one of the bases in the gene for an enzyme could affect the functioning of that enzyme.
The change in base changes the triplet/codon meaning the amino acid it codes for changes and there will therefore be a different sequence of main-acids. This means the polypeptide will fold into a differently shaped portion/enzyme and it may have. differently shaped active site so may not be complementary to the substrate.
35
How many codons and thus amino acids are affected by a substitution mutation?
1
36
What happens in insertion mutations
An extra base is added into the DNA base sequences
37
What is the effect of an insertion and deletion mutation
Changes the way the group of codons are read, which can in turn change the amino acids they code for. Insertions and deletions have a knock on affect and can therefore change more than one amino acid.
38
What are deletion mutations
When a random base is deleted from the DNA base sequence
39
What is sexual reproduction
Where genetic information from two organisms are combined to produce an offspring which are genetically different to either parent
40
In sexual reproduction what do the mother and father produce
Gametes
41
In humans. how many chromosomes to each gamete contain
23 chromosomes - half the number of chromosomes in a normal cell
42
What type of reproduction produces genetically identical cells and what type produces genetically different cells
Asexual reproduction - genetically identical
Sexual reproduction - genetically different
43
Why are the cells genetically identical in asexual reproduction
In asexual reproduction there's only one parent and happens by mitosis
44
How are gametes produced
By meiosis
45
Where does meiosis take place in humans
Only happens in the reproductive organs (the ovaries in females and testes in males)
46
How does meiosis work
Before cells start to divide it duplicates in genetic information forming two identical armed chromosomes - after replication the chromosomes arrange themselves into pairs
In the first division the chromosome pairs line up in the centre of the cell and then are pulled apart so each new cell only has one copy of each chromosomes - some of the fathers and some of the mothers chromosomes go into each cell
In the second division the chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
47
What is the end result of meiosis
You get 4 gametes each with only a single set of chromosomes in it. Each of the gametes are genetically different from one another because all the chromosome get shuffled up during meiosis and each gamete only get half of them at random.
48
What happens once two gametes have fused during fertilisation
The resulting new cell divides by mitosis to make a copy of itself. Mitosis repeats many times to produce lots of new cells in an embryo. As the embryo develops, these cells then start to differentiate into different types of specialised cells that make up a whole organism.
49
When bacteria produce asexually which process do they use?
binary fission
50
Advantages of sexual reproduction
Causes variation in offspring which increases the chance of species surviving a change in environment.
Can use selective breeding which speeds up natural selection - helps to increase food production
Less susceptible to disease
51
How does variation increase the chance of survival in a change in environment
It's likely that variation will have led to some of the offspring being able to survive in the new environments. They have a survival advantage. Individuals with characteristics that make them better adapted to the environment have a better chance of survival, they are more likely to breed successfully and pass the genes for the characteristics on - natural selection
52
What is selective breeding
Produce animals with desirable characteristics. Selective breeding is where individuals with a desirable characteristic are bred to produce offspring that have the desirable characteristics too.
53
Advantages of asexual reproduction
There only needs to be one parent
Asexual reproduction uses less energy than sexual reproduction, because organisms don't have to find a mate
It is faster than sexual reproduction
Many identical offspring can be produced in favourable conditions
54
Organisms that reproduce both sexually and asexually
Parasites reproduce sexually when it's in the mosquito and then asexually when it's in the human host
Fungus produce spores. Spores can be produced sexually and asexually. Sexually produced spores introduce variation and are often produced in response to an unfavourable change in the environment, increasing the chance that the population will survive the change.
Plants - strawberry plants produce runners asexually that are stems that grow horizontally on the surface of the soil away from the plant. At various points along the runner a new straewberry plant forms that is identical to the original plant.
Bulbs - new bulbs can form from the main bulb and divide off. Each new bulb can grow into a new identical plant.
55
What is a genotype
the combination of alleles
56
what is a phenotype
what characteristics you have due to the combination of alleles
57
How do you set out a punnet square
Put the female gametes’ genotype on one side and the male’s genotype on the other
58
What will punnet squares show you
The possible gamete combinations - offspring’s genotypes are shown in the squares
59
What is cystic fibrosis caused by
Caused by a recessive allele
60
What does cystic fibrosis result in
The body producers a lot of thick sticky mucus in the air passages and in the pancreas
61
For a child to have cystic fibrosis what gene do their parents have to carry?
For a child to have the disorder, both parents must be either carriers or have the disorder themselves.
62
What is polydactyly
Genetic disorder where a baby’s born with extra fingers or toes.
63
What causes polydactyly
Caused by a dominant allele
64
How can embryos be screened for genetic disorders
During IVF embryos are fertilised in the laboratory and then implanted into the mothers womb. Before being implanted it’s possible to removes a cell from each embryo and analysis it’s genes.
You could also get DNA from an embryo in the womb and test for disorders
65
Arguments against embryonic screening
after screening, embryos with ‘bad’ alleles would be destroyed.
it implies that people with genetic problems are somehow "undesirable"which could increase prejudice
There may come a point where everyone wants to screen embryos so that they can pick the most desirable one
expensive
66
Arguments for embryonic screening
Will help to stop people suffering
Treating disorders costs the government a lot of money
There are laws to stop it going too far
67
What did Mendel experiment with
Pea plants
68
What did Mendel first notice about plants
He noticed that plants characteristics where passed down from one generation to the next
69
What 3 important conclusions did Mendel reach after the height of pea plant experiment
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 recessive or dominant - if the individual has both the dominant and recessive unit for the characteristics then the dominant characteristic will be expressed
70
Why did it take a while for people to accept Mendel's work
They didn't have background knowledge to properly understand his findings - they were not aware of genes, DNA or chromosomes
71
What are the two types of variatrion
Genetic variation and environmental variation
72
What are alleles
Alternative forms of the same gene
73
What did Mendel study?
The inheritance of different charecteristics
74
What three traits did Mendel study
Colour of peas
Colour of flowers
Height
75
What causes genetic variation
The combining of genes from your mother and father
76
what is environmental variation due to
due to the different environments in which the individual members of the species are in
77
How do mutations introduce variation
Although very rare, genetic mutations can lead to a new phenotype being seen in a species. If the environment changes, and the new phenotype makes an individual more suited to the new environment, it can become common throughout the species relatively quickly by natural selection.
78
What did Darwin conclude from his observations
The organisms with the most suitable characteristics for the environment would be more successful competitors and would be more likely to survive. These organisms are then more likely to reproduce and pass on the genes for the characteristics that helped them survive, ton their offspring. Overtime, beneficial characteristics become more common in the population and the species changed - it evolves
79
What is speciation
The development of new species
80
How does speciation work
Over a long period of time, 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 - this means they can't interbreed to produce fertile offspring.
81
What is extinction
When no individuals of a species remain
82
Reasons why species may become extinct
The environment changes too quickly
A new predetor kills them all
A new disease kills them all
They can't compete with another species for food
` catastrophic event happens that kills them all
83
Why was Darwin's work disputed by some
It went against religious beliefs
Darwin couldn't explain why these new ,useful characteristics appeared or how they were passed on
There wasn't enough evidence
84
Who posed a different scientific hypothesis to Darwin
Lamarck
85
What did Lamarck argue
Argued that changes that an organisms acquires during it's lifetime, will be passed on to it's offspring
86
What is selective breeding
When humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the species.
87
Basic process for selective breeding
From existing stock, select ones that have desirable characteristics
Breed with each other
Select the best of the offspring and breed them together
Continue this process over several generations, and the desirable trait gets stronger and stronger
88
Draw back of selective breeding
Reduction in the gene pool (the number of different alleles in a population). This is because there is inbreeding
89
What can inbreeding cause
Can cause health problems because there is more chance of the organisms inheriting genetic defects when the gene pool is limited
Also serious problems if a new disease appears, as there is not much variation in the population
90
What is genetic engineering
Transfers a gene responsible for a desirable characteristic from one organism's genome into another organism, so that it also had a desired characteristic
91
How does the process of genetic engineering work
- A useful gene is isolated from one organism's genome using enzymes and is inserted into a vector
- The vector is introduced to the target organism, the useful gene is inserted into it's cells
92
What vector is used for genetic engineering
Usually a virus or a bacterial plasmid depending on the type of organism that the gene is being transferred to
93
What can genetic engineering be used for
- Bacteria have been genetically modified to produce human insulin that can be used to treat diabetes
- GM crops have had their genes modifies
- Sheep have been GMed 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 (gene therapy)
94
What are concerns about genetic engineering
long term effects - changing organism's genes might accidentally create unplanned problems, which could get passed on to future generations.
95
Pros of GM crops
- Can increase the yield making more food
- People living in developing nations often lack nutrients in their diet so GM crops could be engineered to contain nutrients that's missing
GM crops are already being grown in some places without any problems
96
Cons of GM crops
- May affect the number of wild flowers and therefore reduce biodiversity
- Could be unsafe and might not fully understand the effects of eating them on human health
- transplanted genes may get out into the natural environment which may create 'super weeds'
97
Traits that could be altered by GM in crops
Increased yield e.g. bigger fruit
Increase quality e.g. better taste
Resistance to disease
Resistance to insects
Resistance to herbicides
Resistance to droughts
98
Two ways plants can be clones
- Tissue culture
- Cuttings
99
How can plants be cloned through tissue culture
A few plants are put in a growth medium with hormones, and they grow into new plants - clones of the parent plant
100
How can plants be cloned through cuttings
Gardeners can take cuttings from good parent plants, and then plant them to produce genetically identical copies of the parent plant. These plants can be produced quickly and cheaply.
101
Ways of making animal clones
Embryo transplant
Adult cell cloning
102
How to make animal clones using adult cell cloning
Take an egg cell from a donor female and remove its nucleus so that you have an 'enucleated' egg cell
Take an adult body cell from the organism you want to clone and remove it's nucleus
Put the adult body cell nucleus into the enucleated egg cell
Stimulate the cell via a small electric shock, it will act like a zygote and divide by mitosis, forming an embryo
Implant the embryo into a uterus of a surrogate mother. It will then develop into a fetus and be born like normal
103
How to make animal clones using embryo transplant
Take sperm cells from prize bull and egg cells from prize cow. Sperm cells then used to artifically fertilise the egg cell. The embryo that develops is then split many times, to form clones before any cells become specialised
These cloned embryos can then be implanted into lots of other cows where they grow into baby calves
104
Issues surrounding cloning
- reduced gene pool
- animals might not be as healthy
- some people worry that humans might be cloned in the future which could be dangerous
105
Pros of cloning
Used to preserve endangered species
106
What type of nucleus is used in adult cell cloning?
A diploid nucleus
107
What are fossils
The remains of organisms from many thousands of years ago, which are found in rocks.
108
What are the ways that fossils form in rocks
- from gradual replacement by minerals
- from casts and impressions
- from preservation in places where no decay happens
109
How do fossils form in gradual replacement by minerals
Hard body parts, such as bones and shells, which
decay very slowly, are gradually replaced by
minerals , forming rock-like substances.
110
How do fossils form from casts and impressions
Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.
111
Which part of a human body cell is affected by cystic fibrosis?
Cell membrane
112
How do fossils form from preservation
Some parts of organisms may not decay at all. For example, dead animals and plants can be preserved in
amber, peat bogs, tar pits, or in ice.
113
What to fossils show
Show how much or how little different organisms have evolved over time
114
Why is the fossil record incomplete?
Some fossils formed long ago may have been destroyed since
Some organisms are soft-bodied so do not fossilise well
115
Why might a dead animal be preserved in a tar pit, rather than decay?
Tar pits do not have any oxygen meaning the decaying microbes cannot survive
116
Ways in which a species might become extinct
Rapid environment change such as an increase in temperature
Reduction in habitat as it could reduce food and living space
Increase hunting as individuals are directly killed
The spread of a new disease
Introduction of a new competitor or predator
A catastrophic event, such as an asteroid strike
117
What is speciation
The development of a new species
118
What is a species
A group of similar organisms that can reproduce to giver fertile offspring
119
When does speciation occur
When populations of the same species become so different that they no longer successfully interbreed to produce fertile offspring
120
What leads to speciation
isolation and natural selection
121
How can isolation lead to speciation
Isolation is where populations of a species are separated. Conditions on either side will be slightly different (different climates). Because the environment is different on both sides different characteristics will become more common in each population due to natural selection operating differently on the populations. Eventually individuals from the different populations will have changed so much that they won't be able to breed with one another to produce fertile offspring.
122
Why does each population show genetic variation in isolation of species
Because they have a wide range of alleles.
123
Who was a pioneer of the theory of speciation
Alfred Russel Wallace
124
What observations did Wallace make
He realised that warning colours are used by some species to deter predators from eating them and that this was an example of beneficial characteristics that had evolved by natural selection
125
How can bacteria become resistant to antibiotics
Bacteria sometimes develop random mutations in their DNA. These can lead to changes in the bacteria's characteristics which can lead to antibiotic- resistant strains forming as the gene for antibiotic resistance becomes more common in the population.
The anti-biotic resistant genes live longer and reproduces many more times. This increases the population size of the resistant strain.
126
Why can bacteria evolve quickly
Because they are so rapid at reproducing
127
Why is antibiotic resistant strains a problem
The bacterial infection could spread between people as there is no effective treatment.
128
What is MRSA
Common 'superbug' (resistant to most known antibiotics) that's really hard to get rid of. IT often affects people in hospital and can be fatal if it enters the blood stream.
129
Why is the problem of antibiotic resistance getting worse
- overuse of inappropriate use of antibiotics (doctors prescribing them for non-serious conditions or infections caused by a virus)
- farmers often give antibiotics to animals to prevent them getting ill and make them grow faster.
130
Ways to help prevent antibacterial resistance
Finishing the course of antibiotics to make sure that all the bacteria are destroyed, which means that there are none left to mutate and develop into antibiotic resistance strains.
Some countries restrict the use of antibiotics for farming
131
According to Lamark why do giraffes have long necks
Giraffes started with short necks adapted to lower vegetation.
They stretched their necks to reach higher branches for food, resulting in longer necks during an individual's lifetime.
This acquired longer neck trait was passed to offspring, and successive generations have longer necks for reaching higher branches.
132
What type of bonds hold together two strands of DNA
Hydrogen
133
According to Wallace and Darwin why do giraffes have long necks
Some giraffes had longer necks than others, due to variation within the species.
Giraffes with longer necks were better adapted to their environment, as they could eat leaves from taller trees.
Giraffes with longer necks had a higher chance of surviving and reproducing, and passed on the trait of long necks to their offspring.
Over many generations, this process produced modern giraffes, with very long necks.
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