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Biology - Inheritance, variation and evolution Flashcards

1
Q

How many strands is the helix structure of DNA made up of

A

2

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2
Q

The DNA in typical human cells is found in tight coils known as

A

chromosomes

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3
Q

How many chromosomes are there in a typical human cell

A

46 - the human has 23 pairs of chromosmes

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4
Q

The chromosomes in the 23rd pair are known as

A

Sex chromosomes

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5
Q

Do women have XX or XY chromosomes

A

XX

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5
Q

What is a gene

A

A small section of DNA that codes for a specific protein

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6
Q

What does the term genome mean

A

The entire set of genetic material in an organism

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7
Q

What are alleles

A

Different versions of a particular gene

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8
Q

What does homozygous mean

A

Both alleles are the same

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9
Q

Dominant allele meaning

A

It will be expressed over the recessive allele

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10
Q

Genotype meaning

A

Two alleles present for a particular gene

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11
Q

Phenotype meaning

A

The characteristics an organism has as a result of their genotype

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12
Q

What are the monomers of DNA

A

Nucleotides

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13
Q

What are the 4 types of bases in DNA

A

Adenine
Thymine
Cytosine
Guanine

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14
Q

What are the complementary baes

A

A always has to pair with T
C always has to pair with G

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15
Q

What codes for a specific amino acid

A

Each set of three bases (triplets)

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16
Q

Main functions of proteins

A

Speed up the rate of chemical reactions - enzymes
Carry messages around the body (hormones)

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17
Q

What is a section if a DNA that codes for a protein called

A

gene

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17
Q

What is transcription in protiensynthesis

A

The copying of a single gene of DNA, to mRNA

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18
Q

Where does transcription take place

A

Nucleus

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19
Q

Why dies a gene of DNA have to be copied to mRNA

A

DNA is too large to leave in the nucleus

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20
Q

Difference between mRNA and DNA

A

mRNA is shorter than DNA
mRNA is single stranded, but DNA is double stranded

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21
Q

Where does the mRNA go once it leaves the nucleus and enters the cytoplasm

A

Ribosome

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22
Q

What is translation in terms of protein synthesis

A

The combination of amino acids to form a polypeptide

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23
Q

How many bases are needed to code for one amino acid

A

3

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24
Q

What is the function of a ribosome?

A

To assemble proteins from amino acids

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25
Q

What is a chain of amino acid called

A

Polypeptide

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26
Q

What is a mutation?

A

A change in the base sequence of an organisms DNA

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27
Q

What is a triplet/ codon?

A

A set of 3 bases which codes for one amino acid

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28
Q

What happens if there ia a mutation to one of the bases in DNA

A

It can change the amino acid that the codon codes for

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29
Q

What is the most likely result of a genetic mutation

A

No significant change to the organism

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30
Q

Most mutations occur in

A

non-coding DNA

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31
Q

What does non-coding DNA do

A

Controls the expression of coding DNA

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32
Q

What does it mean for a gene to be expressed?

A

It’s turned on, so the proteins it codes for will be produced

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33
Q

What happens in a substitution mutation

A

One base in a sequence is replaced with a different base

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34
Q

Describe how a change of one of the bases in the gene for an enzyme could affect the functioning of that enzyme.

A

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.

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35
Q

How many codons and thus amino acids are affected by a substitution mutation?

A

1

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36
Q

What happens in insertion mutations

A

An extra base is added into the DNA base sequences

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37
Q

What is the effect of an insertion and deletion mutation

A

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.

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38
Q

What are deletion mutations

A

When a random base is deleted from the DNA base sequence

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39
Q

What is sexual reproduction

A

Where genetic information from two organisms are combined to produce an offspring which are genetically different to either parent

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40
Q

In sexual reproduction what do the mother and father produce

A

Gametes

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41
Q

In humans. how many chromosomes to each gamete contain

A

23 chromosomes - half the number of chromosomes in a normal cell

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42
Q

What type of reproduction produces genetically identical cells and what type produces genetically different cells

A

Asexual reproduction - genetically identical
Sexual reproduction - genetically different

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43
Q

Why are the cells genetically identical in asexual reproduction

A

In asexual reproduction there’s only one parent and happens by mitosis

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44
Q

How are gametes produced

A

By meiosis

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45
Q

Where does meiosis take place in humans

A

Only happens in the reproductive organs (the ovaries in females and testes in males)

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46
Q

How does meiosis work

A

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.

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47
Q

What is the end result of meiosis

A

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.

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48
Q

What happens once two gametes have fused during fertilisation

A

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.

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49
Q

When bacteria produce asexually which process do they use?

A

binary fission

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50
Q

Advantages of sexual reproduction

A

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

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51
Q

How does variation increase the chance of survival in a change in environment

A

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

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52
Q

What is selective breeding

A

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.

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53
Q

Advantages of asexual reproduction

A

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
Q

Organisms that reproduce both sexually and asexually

A

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
Q

What is a genotype

A

the combination of alleles

56
Q

what is a phenotype

A

what characteristics you have due to the combination of alleles

57
Q

How do you set out a punnet square

A

Put the female gametes’ genotype on one side and the male’s genotype on the other

58
Q

What will punnet squares show you

A

The possible gamete combinations - offspring’s genotypes are shown in the squares

59
Q

What is cystic fibrosis caused by

A

Caused by a recessive allele

60
Q

What does cystic fibrosis result in

A

The body producers a lot of thick sticky mucus in the air passages and in the pancreas

61
Q

For a child to have cystic fibrosis what gene do their parents have to carry?

A

For a child to have the disorder, both parents must be either carriers or have the disorder themselves.

62
Q

What is polydactyly

A

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

63
Q

What causes polydactyly

A

Caused by a dominant allele

64
Q

How can embryos be screened for genetic disorders

A

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
Q

Arguments against embryonic screening

A

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
Q

Arguments for embryonic screening

A

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
Q

What did Mendel experiment with

A

Pea plants

68
Q

What did Mendel first notice about plants

A

He noticed that plants characteristics where passed down from one generation to the next

69
Q

What 3 important conclusions did Mendel reach after the height of pea plant experiment

A

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
Q

Why did it take a while for people to accept Mendel’s work

A

They didn’t have background knowledge to properly understand his findings - they were not aware of genes, DNA or chromosomes

71
Q

What are the two types of variatrion

A

Genetic variation and environmental variation

72
Q

What are alleles

A

Alternative forms of the same gene

73
Q

What did Mendel study?

A

The inheritance of different charecteristics

74
Q

What three traits did Mendel study

A

Colour of peas

Colour of flowers

Height

75
Q

What causes genetic variation

A

The combining of genes from your mother and father

76
Q

what is environmental variation due to

A

due to the different environments in which the individual members of the species are in

77
Q

How do mutations introduce variation

A

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
Q

What did Darwin conclude from his observations

A

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
Q

What is speciation

A

The development of new species

80
Q

How does speciation work

A

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
Q

What is extinction

A

When no individuals of a species remain

82
Q

Reasons why species may become extinct

A

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
Q

Why was Darwin’s work disputed by some

A

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
Q

Who posed a different scientific hypothesis to Darwin

A

Lamarck

85
Q

What did Lamarck argue

A

Argued that changes that an organisms acquires during it’s lifetime, will be passed on to it’s offspring

86
Q

What is selective breeding

A

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
Q

Basic process for selective breeding

A

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
Q

Draw back of selective breeding

A

Reduction in the gene pool (the number of different alleles in a population). This is because there is inbreeding

89
Q

What can inbreeding cause

A

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
Q

What is genetic engineering

A

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
Q

How does the process of genetic engineering work

A
  • 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
Q

What vector is used for genetic engineering

A

Usually a virus or a bacterial plasmid depending on the type of organism that the gene is being transferred to

93
Q

What can genetic engineering be used for

A
  • 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
Q

What are concerns about genetic engineering

A

long term effects - changing organism’s genes might accidentally create unplanned problems, which could get passed on to future generations.

95
Q

Pros of GM crops

A
  • 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
Q

Cons of GM crops

A
  • 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
Q

Traits that could be altered by GM in crops

A

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
Q

Two ways plants can be clones

A
  • Tissue culture
  • Cuttings
99
Q

How can plants be cloned through tissue culture

A

A few plants are put in a growth medium with hormones, and they grow into new plants - clones of the parent plant

100
Q

How can plants be cloned through cuttings

A

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
Q

Ways of making animal clones

A

Embryo transplant
Adult cell cloning

102
Q

How to make animal clones using adult cell cloning

A

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
Q

How to make animal clones using embryo transplant

A

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
Q

Issues surrounding cloning

A
  • 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
Q

Pros of cloning

A

Used to preserve endangered species

106
Q

What type of nucleus is used in adult cell cloning?

A

A diploid nucleus

107
Q

What are fossils

A

The remains of organisms from many thousands of years ago, which are found in rocks.

108
Q

What are the ways that fossils form in rocks

A
  • from gradual replacement by minerals
  • from casts and impressions
  • from preservation in places where no decay happens
109
Q

How do fossils form in gradual replacement by minerals

A

Hard body parts, such as bones and shells, which
decay very slowly, are gradually replaced by
minerals , forming rock-like substances.

110
Q

How do fossils form from casts and impressions

A

Animals can leave impressions or casts, such as footprints or burrows. These become covered by layers of sediment, which eventually become rock.

111
Q

Which part of a human body cell is affected by cystic fibrosis?

A

Cell membrane

112
Q

How do fossils form from preservation

A

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
Q

What to fossils show

A

Show how much or how little different organisms have evolved over time

114
Q

Why is the fossil record incomplete?

A

Some fossils formed long ago may have been destroyed since
Some organisms are soft-bodied so do not fossilise well

115
Q

Why might a dead animal be preserved in a tar pit, rather than decay?

A

Tar pits do not have any oxygen meaning the decaying microbes cannot survive

116
Q

Ways in which a species might become extinct

A

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
Q

What is speciation

A

The development of a new species

118
Q

What is a species

A

A group of similar organisms that can reproduce to giver fertile offspring

119
Q

When does speciation occur

A

When populations of the same species become so different that they no longer successfully interbreed to produce fertile offspring

120
Q

What leads to speciation

A

isolation and natural selection

121
Q

How can isolation lead to speciation

A

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
Q

Why does each population show genetic variation in isolation of species

A

Because they have a wide range of alleles.

123
Q

Who was a pioneer of the theory of speciation

A

Alfred Russel Wallace

124
Q

What observations did Wallace make

A

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
Q

How can bacteria become resistant to antibiotics

A

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
Q

Why can bacteria evolve quickly

A

Because they are so rapid at reproducing

127
Q

Why is antibiotic resistant strains a problem

A

The bacterial infection could spread between people as there is no effective treatment.

128
Q

What is MRSA

A

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
Q

Why is the problem of antibiotic resistance getting worse

A
  • 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
Q

Ways to help prevent antibacterial resistance

A

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
Q

According to Lamark why do giraffes have long necks

A

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
Q

What type of bonds hold together two strands of DNA

A

Hydrogen

133
Q

According to Wallace and Darwin why do giraffes have long necks

A

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.

134
Q
A
135
Q
A

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