B6- Inheritance, Variation and Evolution Flashcards
What are chromosones
Really long molecules of DNA
What does DNA stand for
DeoxyriboNucleic acid
What is DNA
It’s a chemical that all of the genetic material is made up form
What determines your inherited characteristics
DNA
Is DNA a polymer
Yes
What is the shape of DNA called
Double helix structure
What is gene a code for
Specific protein
What is a gene
A small section of DNA found on a chromosome
What does each gene code for
A particular sequence of amino acids which put together to make a specific protein
How many amino acids are there
20
Does every organism have a genome
Yes
Why is understanding the human genome is a really important tool for science and medicine
- It allows scientists to identify genes in the genome that are linked to different typed of disease
- Knowing which genes are linked to inherited diseases could help us to understand them better and could help us to develop effective treatments for them
3 Scientists can look at genomes to trace the migration of certain populations of people around the worlds. All modern humans are descended from a common ancestor who lived in Africa. The human genome is mostly identical in all individuals, but as different populations of people migrated away from Africa, they gradually developed tiny difference in their genomes. By investigating these differences, scientists can work out when new populations split off in a different direction and what route they took.
DNA molecules contain a _ code that determines which proteins are built
Genetic
What is DNA made up of
Nucleotides
What are DNA strands
Polymers made up of loads of repeating units called nucleotides
What does each nucleotide consist of
One sugar molecule, one phosphate molecule and one ‘base’
What does each base (DNA) link to
A base on the opposite strand in the helix
What is each amino acid coded for
By a sequence of three bases in the gene
What does mRNA do
It carries the code to the Ribosomes
Proteins are made in the cell _ on tiny structures called _
Cytoplasm
Ribosmes
Define enzyme
Act as a biological catalysts to speed up chemical reactions in the body
Define hormones
Used to carry messages around the body
What are structural proteins
Are physically strong E.g. collagen is a structural protein that strengths connective tissues (like ligaments and cartilage)
What is a mutation
When the sequence of DNA bases can be changed
Can mutations be inherited
Yes
Are enzymes proteins
Yes
What are insertions mutations
Where a new base is inserted into the DNA base sequence where it shouldn’t be
What are deletions mutations
- Deletions are when a random base is deleted form the DNA base sequence
- Like insertions, they change the way that the base sequence is ‘ read’ and have knock-on effects further down the sequence
What are substitutions mutations
Are when a random base in the DNA base sequence is changed to a different base
How many chromosomes are in gamete cells have
23
What are gametes
Egg and sperm
What does asexual reproduction produce
Genetically identical cells
Describe asexual reproduction
There’s only one parent. There’s no fusion of gametes, no mixing of chromosomes and no genetic variation between parent and offspring. The offspring are genetically identical to the parent - they’re clones
What organisms do asexual reproduction
Bacteria, some plants and some animals reproduce asexually
What is cystic fibrosis
A genetic disorder of the cell membrane. It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas
What is polydactyly caused by
A dominent allele
What is polydactyly
A genetic disorder where a baby’s born with extra fingers or toes. It doesn’t usually cause any other problems so isn’t life-threatening
Why are some people against Embryonic Screening
- 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
- Expensive
Why are some people for Embryonic Screening
- It will help to stop people suffering
- Treating disorders costs the Government 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
What did Mendal experiment with/on
Mendal did experiments with Pea plants
Who was Gregor Mendal
An Austrian monk who trained in maths and natural history at the University of Vienna
What did Mendal show
That the height characteristics in pea plants was determined by separately inherited “hereditary units” passed on form each parent. The ratios of tall and dwarf plants in the offspring showed that the unit for tall plants,T, was dominant over the unit for dwarf plants,t.
What were Mendel 3 conclusions
- 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 dominant or recessive - if an individual has both the dominant and the recessive- if an individual has both the dominant and the recessive unit for a characteristic, the dominant characteristic will be expressed
What is the theory of evolution
All of today’s species have involved from simple life forms that first started to develop over three billion years ago
What are the 5 reasons species become extinct
- The environment changes too quickly
- A new predator kills them all
- Disease
- They can’t compete with another species for food
- A catastrophic event happens that kills them all
What were reasons as to why some people don’t believe in evolution
- Religious beliefs
- Darwin couldn’t explain why new useful characteristics appear
- Not enough evidence
What was Jean-Baptiste believe (in terms of evolution)
Changes that an organism acquires during its lifetime will be passed on to its offspring
What was Lamarck’s hypothesis about evolution
Eventually rejected because experiments didn’t support his hypothesis. You can see it fir your=self
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 population
What is the main disadvantage of selective breeding
Smaller gene pool
What is genetic engineering
Transferring genes between organisms
Why is genetic engineering a controversial topic
- It is an existing area of science, which has the potential for solving many of our problems, but not everyone thinks it’s a great idea
- There are worries about the long-term effects of genetic engineering- that changing an organism’s genes might accidentally create unplanned problems, which could get passed on to future generations
What are pros of GM crops
- The characteristics chosen for GM crops can increase the yields, making more food
- People living in developing nations often lack nutrients in their diets
- GM crops are already being grown in some places, often without any problems
What are cons of GM crops
- Some people say that growing GM crops will affect the number of wild flowers that live in and around the crops- reducing farmland biodiversity
- Not everyone is convinced that GM crops are safe and some people are concerned that we might not fully understand the effects of eating them on human health
- A big concern is that transplanted genes may get out into the natural environment
How can plants be cloned
Tissue culture and from cuttings
What is tissue culture
This is where a few plants cells are put in a growth medium with hormones, and they grow into new plants- clones of the parent plant. These plants can be made very quickly, in very little space, and be grown all year. Tissue culture is used by scientists to preserve rare plants that are hard to reproduce naturally and by plant nurseries to produce lots of stock quickly
What is cuttings (cloning)
- Gardeners can take cuttings from good parent plant, and then plant them to produce genetically identical copies (clones) of the parent plant
- These plants can be produced quickly and cheaply. This is an older, simpler method than tissue culture
How do farmers produce cloned offspring from their best bull and cow
- Sperm cells are taken from a prize bull and egg cells are taken from a prize cow. The sperm are then used to artificially fertilise an egg cell. The embryo that develops of then split many rimes (to form clones) before any cells become specialised
- These cloned embryos can them be implanted into lots of other cows where they grow into calves ( which will all be genetically identical to each other)
- Hundreds of “ideal” offspring can be produced every year from the best bull and cow
What is adult cell cloning
- It unfertilised taking an unfertilised egg cell and removing its nucleus. The nucleus is then removed from an adult body cell and is inserted into the ‘empty’ egg cell.
- the egg cells is then stimulated by an electric shock- this makes it divide, just like a normal embryo
- When the embryo is a ball of cells, it’s implanted into the womb of an adult female. It grows into a genetically identical copy (clone) of the original adult body cell as it has the same genetic information
What are the issues surrounding cloning
- Cloning quickly gets lots of “ideal” offspring. But you also get a “reduced gene pool”
- Cloned animals might not be as healthy as normal ones
- Some people worry that humans might be cloned in the future
What are pros surrounding cloning
- The study of animal clones could lead to greater understanding of the development if the embryo, and of ageing and age-related disorders
- Cloning could also be used to help preserve endangered species
What are the three ways fossils form
- From gradual replacement by minerals
- From cats and impressions
- From preservation in places where no decay happens
Explain how fossils are made with the from gradual replacement by minerals
- things like teeth, shells, bones etc… 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 sediment also turn to rock, but the fossil stays distinct inside the rock and eventually someone digs it up
Explain how fossils are made with the from cats and impressions
- Sometimes, fossils are formed when an organism is buried in a soft material like clay. the clay later hardens around it and the organism decays, leaving a cast of itself. An animal’s burrow or a plant’s roots can be preserved as casts
- Things like footprints like footprints can also be pressed into these materials when soft, leaving an impression when it happens
Explain how fossils are made with the 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 microbes.
What is speciation
The development if a new species
Define species
A group of similar organisms that can reproduce to give a fertile offspring
When does speciation happen
When the population of the same species become so different that they can no longer successfully interbreed to produce fertile offspring
What is isolation (in terms in speciation)
Where populations of a species are separated
Who was Alfred Russel Wallace
A scientists working at the same time as Charles Darwin. He was one of the early scientists working on the idea of speciation.
Who came up with the idea of natural selection
Alfred Russel Wallace
What is classification
Organising living organisms into groups
What is archaea
Organisms in this domain were once thought to be primitive bacteria, but they’re actually a different type of prokaryotic cell. They were first found in extreme places such as hot springs and salt lakes
What is eukaryota
This domain includes a broadrange of organisms including fungi, plants, animals and protsist
What do evolutionary trees show
Evolutionary relationship
What is gene code for
A small section , protiens
List the parts of a DNA nucleotide
phosphate, a sugar called deoxyribose, and four nitrogenous bases—adenine, guanine, cytosine, and thymine.
How many bases in a DNA sequence code for one amino
Three
Give a function of the non-coding parts of DNA
Functions of non-coding DNA include the transcriptional and translational regulation of protein-coding sequences, scaffold attachment regions, origins of DNA replication, centromeres and telomeres.
Explain how mutations can lead to a change in the protein coded for by a gene
This alteration occurs during translation because ribosomes read the mRNA strand in terms of codons, or groups of three nucleotides. These groups are called the reading frame.
True or false : Most mutations have little or no effect om the protein coded for by a gene
False
Name the male and female gametes of animals
Egg and sperm
Which type of reproduction produces genetically identical cells
Asexual reproduction
State the type of cell division used to make gametes in humans
meiosis
How does variation in a population increase its chance of surviving environmental change
Variation allows some individuals within a population to adapt to the changing environment
Describe the methods of sexual and asexual reproduction used by strawberry plants
Strawberry plants can be propagated asexually by allowing plantlets on the ends of stolons (“runners”) to grow in soil. But the actual strawberries are the result of sexual reproduction, as they grow from flowers.
What is the probability that offspring will have the XX combination of sex chromosomes
50%
How many genes are responsible for controlling fur colour in mice
Five
What are alleles
Each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
What does it mean if someone is heterozygous for a gene
Heterozygous refers to having inherited different forms of a particular gene from each parent. A heterozygous genotype stands in contrast to a homozygous genotype, where an individual inherits identical forms of a particular gene from each parent.
What is the chance of a child being born with polydactyly if one parent has a sing dominant allele for the gene that controls it
50%
What do we now know Mendel’s “units” as
Genes
What is variation
A change or slight difference in condition, amount, or level, typically within certain limits.
Explain how beneficial characteristics can become more common in a population over time
The species without it become extinct
What was Jean-Baptiste Lamarck’s theory about evolution
Lamarck believed that living things evolved in a continuously upward direction, from dead matter, through simple to more complex forms, toward human “perfection.” Species didn’t die out in extinctions.
How might farmers use selective breeding
Select two parents that have beneficial phenotypic traits to reproduce, yielding offspring with those desired traits.
What is genetic engineering
He deliberate modification of the characteristics of an organism by manipulating its genetic material.
How can embryo transplants be used to create animal clones
The nucleus is removed from an unfertilised egg cell. the nucleus from an adult body cell, such as a skin cell, is inserted into the egg cell. an electric shock stimulates the egg cell to divide to form an embryo.
Give two ways that fossils can be formed
- From gradual replacement by minerals
- From casts and impressions
- From preservation in places where no decay happens
What is speciation and when can it occur
Speciation is the process by which new species form. It occurs when groups in a species become reproductively isolated and diverge.
What leads to the formation of antibiotic-resistant strains of bacteria
A random mutation occurs in the DNA of individual bacterial cells.
Name the groups of organisms are classified into in the Linneaean system
- animals (all multicellular animals)
- plants (all green plants)
- fungi (moulds, mushrooms, yeast)
- protists (amoeba, chlorella and plasmodium)
- prokaryotes (bacteria, blue-green algae)
Who proposed the ‘three-domain system’ of classification in 1990
Woese
What organ produces energy
The pancreas
Why do water levals have to be balanced
○ Too little water cuases the cell to shrivel up/shrink
○ Too much water causes the cell to burst
○ Animal cells don’t have a cell wall to keep the structure
What organ does ‘selctive reabsorbtion’
Kidneys
What is selective reabsorbtion
Taking back the things it wants and leaves other things
Are all or some or no glucose reabsorbed by the kidneys
All
Are all or some or no urea reabsorbed by the kidneys
None of it
Are all or some or no water reabsorbed by the kidneys
Some
What is sexual reproduction
● Type of reproduction.
● Involves the production of gametes by meiosis.
● A gamete from each parent fuses to form a zygote.
● Genetic information from each gamete is mixed so the resulting zygote is unique.
What are gametes
● Sex cells (sperm cells and egg cells in
animals, pollen and egg cells in flowering
plants).
● Haploid (half the number of chromosomes)
What is meiosis
● Form of cell division involved in the formation of
gametes (non-identical haploid cells) in reproductive
organs.
● Chromosome number is halved.
● Involves two divisions
What must occur prior to meiosis
Interphase - copies of genetic
information are made during this
process
What happens during the first stage of meiosis
● Chromosome pairs line up along the cell equator.
● The pair of chromosomes are separated and move to
opposite poles of the cell (the side to which each
chromosome is pulled is random, creating variation).
● Chromosome number is halved.
What happens during the second stage of meiosis
● Chromosomes line up along the cell equator.
● The chromatids are separated and move to opposite
poles of the cell.
● Four unique haploid gametes are produced
Why is meiosis important for sexual reproduction?
2
● It increases genetic variation.
● It ensures that the zygote formed at
fertilisation is diploid
Describe fertilisation and its resulting outcome
Gametes join together to restore the normal
number of chromosomes and the new cell then
divides by mitosis (which increases the number
of cells).
As the embryo develops, cells differentiate
What is the advantage of sexual reproduction
It creates genetic variation in offspring,
increasing the probability of a species adapting to
and surviving environmental changes.
Natural selection can be speeded up by humans
in selective breeding to increase food production
Describe the disadvantages of sexual reproduction
2
● Two parents are required. This makes reproduction
difficult in endangered populations or in species which
exhibit solitary lifestyles.
● More time and energy is required so fewer offspring
are produced
What is asexual reproduction?
● Type of reproduction.
● Involves mitosis only.
● Produces genetically identical offspring
known as daughter cells
Describe the advantages of asexual
reproduction (3)
● Only one parent is required.
● Lots of offspring can be produced in a short period of time,
enabling the rapid colonisation of an area and reducing
competition from other species.
● Requires less energy and time as do not need a mate
What is the disadvantage of asexual reproduction
No genetic variation (except from
spontaneous mutations) reducing the
probability of a species being able to
adapt to environmental change
Describe the circumstances in which malarial
parasites reproduce sexually and asexually
Sexual reproduction in the mosquito.
Asexual reproduction in the human host
Describe the circumstances in which fungi reproduce
sexually and asexually
Asexual reproduction by spores.
Sexual reproduction to give variation
Describe the circumstances in which plants
reproduce sexually and asexually
Sexual reproduction to produce seeds.
Asexual reproduction by runners (e.g.
strawberry plants) or bulb division (e.g.
daffodils).
What is DNA
A double-stranded polymer of nucleotides, wound to form a double helix. The genetic material of the cell found in its nucleus
Define genome
The entire genetic material of an organism
Why is understanding the human genome
important
The whole human genome has been studied and is
important for the development of medicine in the future.
● Searching for genes linked to different types of disease.
● Understanding and treating inherited disorders.
● Tracing human migration patterns from the past
What is a chromosome
A long, coiled molecule of DNA that
carries genetic information in the form of
genes
How many chromosomes do human
body cells have
46 chromosomes (23 pairs)
How many chromosomes do human gametes have
23 chromosomes
Define gene
A small section of DNA that codes for a
specific sequence of amino acids which
undergo polymerisation to form a protein.
What are the monomers of DNA
Nucleotides
What are DNA nucleotides made up of
● Common sugar
● Phosphate group
● One of four bases: A, T, C or G
State the full names of the four bases found in
nucleotides
● Adenine
● Thymine
● Cytosine
● Guanine
Describe how nucleotides interact to form a molecule
of DNA
● Sugar and phosphate molecules join to form a
sugar-phosphate backbone in each DNA strand.
● Base connected to each sugar.
● Complementary base pairs (A pairs with T, C pairs with G)
joined by weak hydrogen bonds.
Explain how a gene codes for a protein
● A sequence of three bases in a gene forms a triplet.
● Each triplet codes for an amino acid.
● The order of amino acids determines the structure
(i.e. how it will fold) and function of protein formed
Why is the ‘folding’ of amino acids
important in proteins such as enzymes
The folding of amino acids determines the
shape of the active site which must be
highly specific to the shape of its substrate.
What is protein synthesis
The formation of a protein from a gene
What are the two stages of protein synthesis
- Transcription
2. Translation
What does transcription involve
The formation of mRNA from a DNA
template
Outline transcription
- DNA double helix unwinds.
- RNA polymerase binds to a specific base sequence of non-coding
DNA in front of a gene and moves along the DNA strand. - RNA polymerase joins free RNA nucleotides to complementary bases
on the coding DNA strand. - mRNA formation complete. mRNA detaches and leaves the nucleus.
What does translation involve
A ribosome joins amino acids in a
specific order dictated by mRNA to form
a protein.
Outline translation
- mRNA attaches to a ribosome.
- Ribosome reads the mRNA bases in triplets. Each triplet codes
for one amino acid which is brought to the ribosome by a tRNA
molecule (carrier molecule). - A polypeptide chain is formed from the sequence of amino
acids which join together
What is a mutation
A random change in the base sequence of DNA which
results mostly in no change to the protein coded for, or
genetic variants of the protein (slight alteration but
appearance and function remain).
Mutations occur continuously.
Describe the effect of a gene mutation in coding
DNA
● If a mutation changes the amino acid sequence, protein
structure and function may change (an enzyme may no longer
fit its substrate binding site or a structural protein may lose its
strength).
● If a mutation does not change amino acid sequence, there is no
effect on protein structure or function
What is non-coding DNA
DNA which does not code for a protein
but instead controls gene expression.
Describe the effect of a gene mutation in
non-coding DNA
Gene expression may be altered,
affecting protein production and the
resulting phenotype
What are alleles
Different versions of the same gene
What is a dominant allele
A version of a gene where only one copy
is needed for it to be expressed
What is a recessive allele?
A version of a gene where two copies
are needed for it to be expressed.
What is meant when an organism is homozygous
When an organism has two copies of the same allele (two recessive or two dominant).
What is meant when an organism is heterozygous
When an organism has two different
versions of the same gene (one
dominant and one recessive).
What is the genotype?
The genes present for a trait
What is the phenotype?
The visible characteristic.
How are dominant alleles represented in
a punnett square
They are represented using uppercase
letters
How are recessive alleles represented in a punnett
square
They use the lowercase version of the
same letter as the dominant allele
What is the problem with single gene crosses
Most characteristics are controlled by multiple alleles rather than just one
What is an inherited disorder
A disorder caused by the inheritance of
certain alleles
Give 2 examples of inherited disorders
● Polydactyly (having extra fingers or toes) -
caused by a dominant allele.
● Cystic fibrosis (a disorder of cell
membranes) - caused by a recessive allele
How are embryos screened for inherited disorders?
During IVF, one cell is removed (from an 8 cell
embryo) and tested for disorder-causing
alleles. If the cell doesn’t have any indicator
alleles, then the originating embryo is
implanted into the uterus
What are the ethical issues concerning embryo
screening?
● It could lead to beliefs in society that being disabled or having a disorder is less human or associated with inferiority.
● The destruction of embryos with inherited disorders is seen by
some as murder as these would go on to become human beings.
● It could be viewed as part of the concept of designer babies as it
may be for the parents convenience or wishes rather than the child’s wellbeing.
What are the economic issues concerning embryo
screening
● Costs of hospital treatment and medication
will need to be considered if it is known that
a child will have an inherited disorder and
financial support explored if necessary
What are the social issues concerning embryo
screening?
● Social care for children with inherited disorders may
need to be considered if parents are unable to provide
care.
● If an embryo is found to have an inherited disorder and
is terminated, this can prevent a child and its parents
from potential suffering in the future due to the disorder
What is gene therapy
The insertion of a normal allele into the
cells of a person with an inherited
disorder to functionally replace the faulty
allele.
What are the ethical issues concerning gene
therapy
● Some people believe that it is going against and ‘playing God’. ● The introduced genes could enter sex cells and so be passed to future generations.
What are sex chromosomes
A pair of chromosomes that determine sex:
● Males have an X and a Y chromosome
● Females have two X chromosomes
Why does the inheritance of a Y chromosome mean
that an embryo develops into a male?
Testes development in an embryo is
stimulated by a gene present on the Y
chromosome
What is a sex-linked characteristic
A characteristic that is coded for by an
allele found on a sex chromosome.
Why are the majority of genes found on the X
chromosome rather than the Y chromosome?
The X chromosome is bigger than the Y
chromosome so more genes are carried on it
Why are men more likely to show the phenotype for
a recessive sex-linked trait than women
● Many genes are found on the X chromosome that have no
counterpart on the Y chromosome.
● Women (XX) have two alleles for each sex-linked gene whereas men
(XY) often only have one allele ∴ only one recessive allele is required
to produce the recessive phenotype in males.
What is variation
Differences in the characteristics of
individuals in a population is called
variation
What are the two causes of variation within a
species
● Genetics
● Environment
● A mixture of both of the above
What is genetic variation
● Variations in the genotypes of organisms of
the same species due to the presence of
different alleles.
● Creates differences in phenotypes.
What creates genetic variation in a species
● Spontaneous mutations
● Sexual reproduction
What is a mutation?
A random change to the base sequence
in DNA which results in genetic variants.
They occur continuously
State the three types of gene mutation
● Insertion
● Deletion
● Substitution
How may a gene mutation affect an organism’s
phenotype? (3)
● Neutral mutation does not change the sequence of amino acids.
Protein structure and function same. No effect on phenotype.
● Mutation may cause a minor change in an organism’s phenotype e.g.
change in eye colour.
● Mutation may completely change the sequence of amino acids. This
may result in a non-functional protein. Severe changes to phenotype
What is the consequence of a new phenotype
caused by a mutation being suited to an
environmental change?
There will be a rapid change in the
species.
What is evolution
● A gradual change in the inherited traits
within a population over time.
● Occurs due to natural selection which may
result in the formation of a new species
Outline the theory of natural selection
All species of living things have evolved from simple life forms that
first developed more than 3 billion years ago.
1. Genetic variation exists due to spontaneous mutations.
2. Selection pressures (e.g. competition, disease) exist.
3. Random mutation gives an organism a selective advantage.
4. Organism is better adapted to the environment and survives.
5. Organism reproduces, passing on its beneficial alleles.
6. Frequency of advantageous alleles increase.
How do two populations become different species
When their phenotypes become different
to the extent that they can no longer
interbreed to produce fertile offspring
What is selective breeding?
The process by which humans artificially select
organisms with desirable characteristics and
breed them to produce offspring with similar
phenotypes
Outline the main steps involved in selective breeding
- Identify a desired characteristic e.g. disease resistance.
- Select parent organisms that show the desired traits and
breed them together. - Select offspring with the desired traits and breed them
together. - Process repeated until all offspring have the desired traits
Give examples of characteristics selected for in
selective breeding
● Disease resistance in crops
● Higher milk or meat production in animals
● Gentle nature in domestic dogs
● Large flowers
What is the main advantage of selective breeding?
Creates organisms with desirable features: ● Crops produce a higher yield of grain ● Cows produce a greater supply of milk ● Plants produce larger fruit ● Domesticated animals
Other than in agriculture, where else is selective
breeding useful
● In medical research
● In sports e.g. horse racing
Outline the disadvantages of selective breeding
● Reduction in the gene pool (which becomes especially
harmful if sudden environmental change occurs).
● Inbreeding results in genetic disorders.
● Development of other physical problems e.g. respiratory
problems in bulldogs.
● Potential to unknowingly select harmful recessive alleles.
What is genetic engineering
● The modification of the genome of an organism by the insertion
of a desired gene from another organism - genes from
chromosomes of humans and other organisms can be ‘cut out’
and transferred to cells of other organisms.
● Enables the formation of an organism with beneficial
characteristics
Give an example of uses for genetically modified
plants.
● Disease resistance
● Produce larger fruits
What is a use for genetically modified bacteria cells
To produce human insulin to treat
diabetes mellitus
Describe the benefits of genetic engineering
● Increased crop yields for growing population e.g.
herbicide-resistance, disease-resistance.
● Useful in medicine e.g. insulin-producing bacteria, anti-thrombin
in goat milk, possibility to overcome some inherited disorders
(being explored in medical research).
● GM crops produce scarce resources e.g. GM golden rice
produces beta-carotene (source of vitamin A in the body).
Describe the risks of genetic engineering
● Long-term effects of consumption of GM crops unknown.
● Negative environmental impacts e.g. reduction in biodiversity, impact
on food chain, contamination of non-GM crops forming ‘superweeds’.
● Late-onset health problems in GM animals.
● GM seeds are expensive. LEDCs may be unable to afford them or
may become dependent on businesses that sell them
What is the name for crops that have
had their genes modified?
Genetically modified (GM) crops e.g.
those modified to be resistant to insect
attack and herbicides
What is Bacillus thuringiensis (Bt)
● Insect larvae are harmful to crops.
● Bt is a bacterium which secretes a toxin
that kills insect larvae.
How is genetic engineering used to protect crops
against insects
● The gene for toxin production in Bt can be
isolated and inserted into the DNA of crops.
● Bt crops now secrete the toxin which kills any
insect larvae that feed on it.
What are the benefits of Bt crops(3)
● Increased crop yields (fewer crops damaged).
● Lessens the need for artificial insecticides.
● Bt toxin is specific to certain insect larvae so is
not harmful to other organisms that ingest it.
What are the risks of Bt crops
● Long term effects of consumption of Bt crops
unknown.
● Insect larvae may become resistant to the Bt
toxin.
● Killing insect larvae reduces biodiversity
Describe the process of genetic engineering
- DNA is cut at specific base sequences by restriction enzymes to
create sticky ends. - Vector DNA cut using the same restriction enzymes to create
complementary sticky ends. - Ligase enzymes join the sticky ends of the DNA and vector DNA
forming recombinant DNA. - Recombinant DNA mixed with and ‘taken up’ by target cells
What is a vector
A structure that delivers the desired gene
into the recipient cell e.g. plasmids,
viruses.
How can plants be cloned? (2)
● Taking plant cuttings
● Tissue culture
What is tissue culture?
Using small groups of cells from part of a
plant to grow identical new plants.
Describe how plants are grown using tissue culture
- Select a plant that shows desired characteristics.
- Cut multiple small sample pieces from meristem tissue.
- Grow in a petri dish containing growth medium.
- Transfer to compost for further growth.
What must be ensured when preparing tissue
cultures?
Ensure aseptic conditions to prevent
contamination by microorganisms
What does the growth medium contain?
Nutrients and growth hormones
What are the advantages of growing
plants by tissue culture? (4)
● Fast and simple process.
● Requires little space.
● Enables the growth of many plant clones with the same
desirable characteristics.
● Useful in the preservation of endangered plant species.
What are the disadvantages of growing plants by
tissue culture? (2)
● Reduction in the gene pool.
● Plant clones often have a low survival rate.
● Could unknowingly increase the presence of harmful
recessive alleles
Describe the plant cuttings method of plant cloning
Older but simpler method than tissue culture.
Gardeners use this method to produce many
identical new plants from a parent plant.
Detail the process of the plant cuttings
method of plant cloning
- A branch is cut off from the parent plant.
- The lower leaves of the branch are removed and the stem is
planted. - Plant hormones are used to encourage new root development.
- A plastic bag is used to cover the new plant to keep it warm and
moist. - New roots and a new plant is formed after a few weeks
What does embryo transplanting involve
● Pre-specialised cells from a developing animal embryo are split apart. ● The resulting separate but identical embryos are transplanted into host mothers.
Describe how adult cell cloning is performed
- The nucleus is removed from an unfertilised egg cell.
- The nucleus from an adult body cell, such as a skin cell, is inserted into
the egg cell. - An electric shock stimulates the nucleated egg cell to divide and it forms
an embryo. - The embryo cells contain the same genetic information as the adult body
cell. - When the embryo is a ball of cells, it is inserted into the uterus of an adult
female to continue developing
Outline the theory of evolution by natural selection
Individuals of a species show a wide range of variation for a
characteristic.
Those with the characteristic most suited to the environment
will survive breed most successfully.
The desirable characteristic that has enabled the individuals
to survive are passed onto their offspring
Why was Darwin’s theory of evolution not accepted
initially
● Most people believed in creationism
● Insufficient evidence to prove the theory
● The mechanism of variation and inheritance
was not known at the time
What was Jean-Baptiste Lamarck’s theory of
inheritance.
That changes during the lifetime of an
organism can be inherited
What is speciation
The formation of a new species, when
two populations become so varied that
they cannot interbreed to produce fertile
offspring
What is the definition of a species
A group of organisms with similar characteristics which are able to interbreed to produce fertile offspring.
Outline the process of speciation through geographic
isolation
● Two populations of the same species are separated geographically
● Geographic isolation prevents interbreeding and mixing of genes
between the populations.
● Due to different selection pressures, different mutations occur
producing different phenotypes in each population.
● Over time, the two populations may evolve so that they are not able to
interbreed
Why is genetic variation important in
speciation?
Genetic variation produces phenotypic variation, some of which are better suited to the environment and are selected for
How did Mendel study inheritance
Through carry breeding experiments on plants and analysing the ratio of characteristics in offspring
Why was Mendel’s work not recognised until after
his death
He could not explain the mechanism of inheritance,
as chromosomes were only discovered after his
death. It was not communicated well to other scientists and not published in a reputable scientific journal
State two kinds of evidence used to show evolution
● Fossils
● Antibiotic resistance in bacteria
How are fossils formed
● Parts of organisms that have not decayed due to
conditions needed for decay being absent.
● Parts of organisms that have been replaced by
minerals as they decayed eg. bones.
● Traces of organisms are preserved, covered in
sediment and becoming rock.
Why are there few traces of early life-forms left
behind
They are mostly soft-bodied
How do fossils act as evidence for evolution
Scientists can identify the ages of the fossils and use them to show how organisms change over time
What do branches in evolutionary trees indicate?
Where speciation has occurred
What is extinction
Where there are no individuals of a species still alive
State the factors that may lead to extinctions.
● New disease ● Predation ● Competition ● Changes to the environment ● Catastrophic events
What enables bacteria to evolve quickly
The fast rate of their reproduction
Outline the process of antibiotic resistance bacteria
evolving.
● Mutations occur in bacteria producing genetic variation.
● Certain strains are resistant to antibiotics and are not
killed when the antibiotic is applied.
● Resistant strains survive and reproduce.
● Over time, the population of the resistant strains increase
Why are resistant strains of bacteria dangerous
People have no immunity to them and there is no effective treatment
State an example of a resistant strain of bacteria
MRSA
What can be done to reduce the rate of development
of antibiotic resistant bacteria
● Refrain from inappropriately prescribing
antibiotics eg. for viral diseases.
● Patients should complete the prescribed course of
antibiotics.
● Restrict agricultural uses of antibiotics
Why is it difficult to keep up with emerging resistance
strains
Developing antibiotics have a high cost
and take a long time to develop
What are the classes of organisms as determined by
Carl Linnaeus
Kingdom, phylum, class, order, family,
genus, species
Which features are living creatures traditionally
classified by
By their structure and characteristics
What is the binomial system of naming
organisms
Genus name followed by species name
Why were new classification models proposed
● Developments in microscopy allowed better
examination of internal structures.
● Improvement in understanding of
biochemical processes.
State the three domains
● Archaea
● Eukarya
● Bacteria
Which organisms belong in the domain Archaea?
Bacteria, usually living in extreme environments
Which organisms belong in the domain Bacteria
Bacteria.
Which kingdoms belong in domain Eukarya
● Plants
● Animals
● Fungi
● Protists
How are evolutionary trees created
By examining the DNA of different
species and analysing how similar the
sequences are
What does sexual reproduction produce
An offspring that is genetically different
What is required for asexual reproduction
One parent
What does asexual reproduction produce
A clone
Name 2 organisms that reproduce asexually
Starfish, strawberries
What is fertilisation
When the sperm and egg fuse
What are gametes
Egg and sperm cell
What is the human male gamete
Sperm
What is the human female gamete
Egg
How many chromosomes are found in gamete
23
What are the advantages of asexual reproduction
It’s fast. This means that more survive. If only one survives or if they aren’t close together
What are the advantages of sexual reproduction
Genetic variation. They can withstand disease
What are the disadvantages of asexual reproduction
There is no genetic variation. It can withstand disease. It’s less adaptable
What are the disadvantages of sexual reproduction
Need time to find a mate. It’s not possible if it’s an isolated government
Define zygote
When the two gametes combine, they merge the two sets of the chromosome to have 46, which are referred to as diploid. This produces a new cell called a zygote, which will mature into an embryo.
What are the male sex cells in a plant
Pollen
What are the female sex cells in a plant
Egg
How many chromosomes does a body cell have
23 pairs (46)
What is the break down of chromosomes in a body cells
One pair is sex chromosomes
Other 22 are autosomes
What does haploid mean
Half the number of chromosones
What does diploid mean
The full amount of chromosomes
What is the break down of chromosomes in sex cells
22 autosomes
1 sex chromosome
Define gibberellins
Seed germination
What are functional proteins
○ Enzymes
○ Hormones
○ Hemoglobin
What are structural proteins
○ Keratin (the stuff in hair and nails)
○ Collagen
○ Muscle
Single gene mutations involve the alteration of a …
DNA nucleotide
Define genome
All the genetic material of an organism
The version of the gene that we have is called an …
Allele
The alleles present are called the ….
Genotype
If two alleles are the same the person is _ for that trait
Homozygous
If the two alleles are different the person is _ for that trait
Heterozygous
