B6: Inheritance, variation and evolution Flashcards
give three features of sexual reproduction
- the production of gametes by meiosis
- a gamete from each parent fuses to form a zygote
- gamete have different genetic information so zygote is unique
what are gametes?
- sex cells ( sperm cell and egg cells in animals ; pollen and egg cells in flowering plants )
- haploid ( half the number of chromosomes)
give three features of meiosis
- form of cell division involved in the formation of gametes in reproductive organs
- chromosome number is halved
- involves 2 divisions
what must occur prior to meiosis?
interphase:
- copies of genetic information are made during this process
why is meiosis important for sexual reproduction?
- it increases genetic variation
- it ensures that the zygote formed at fertilisation is diploid
Describe fertilisation and its resulting outcome
- gametes join together to form a zygote
- the new cell then divides by mitosis
- as the embryo develops, cells differentiate
give three advantages of sexual reproduction
- genetic variation in offspring,
- species can adapt to new environments due to variation, which gives them a survival advantage
- Humans can speed up natural selection through selective breeding, which can 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
give 2 features of asexual reproduction?
- involves mitosis only
- produces genetically identical daughter cells
describe the advantages of asexual reproduction (3)
- only one parent is required
- more time and energy efficient as do not need a mate
- lots of offspring can be produced in a short period of time, when conditions are favourable ( enabling the rapid colonisation of an area and reducing competition from other species)
give a disadvantage of asexual reproduction
- no genetic variation ( except from spontaneous mutations)
- reducing the probability of a species being able to adapt to environmental change
- species may only be suited to one habitat
Describe the circumstances in which malarial parasites reproduce sexually and asexually
- sexual reproduction in the mosquito ( the gut)
- asexual reproduction in the human host ( liver and red blood cells)
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)
Describe the structure of
DNA
- A polymer made up of repeating units called nucleotides.
- The polymer is made up of 2
strands that is twisted into a double helix
Define genome
- the entire genetic material of an organism
give three reasons why understanding the human genome important?
- 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
- DNA + protein
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 particular sequence of amino acids (that undergo polymerisation) to make a specific 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 , G
state the full names of the four bases 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 weakhydrogenbonds.
Explain how a gene codes for a protein (3)
- 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 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 to the shape of its substrate
define protein synthesis
the formation of a protein from a gene
what are the two stages of protein synthesis
- transcription
- translation
what does transcription involve?
the formation of mRNA from a DNA template
explain the process of transcription
- DNA double helix unwinds
- base sequence of the gene is copied into a complementary template molecule ( mRNA)
- mRNA moves from the nucleus into the cytoplasm
what does translation involve:
- a ribosome joins amino acids in a specific order dictated by mRNA to form a protein
describe and explain translation
- mRNA attaches to a ribosome
- amino acids are brought the the ribosome on carrier molecules (tRNA)
- Ribosome reads the mRNA bases in triplets.
- A polypeptide chain is formed from the sequence of amino acids which join together to from a protein
what is a mutation?
- A random change in the base sequence of DNA ( DNA Structure)
Describe the effect of a gene mutation in coding DNA
- if changes sequence
- if not
If a mutation changes the amino acid sequence:
- protein structure and function may change e.g. 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 forms 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 copes are needed for it to be expressed
define homozygous
- when an organism has two copies of the same allele ( two recessive or two dominant)
define heterozygous
- when an organism has two different versions of the same gene ( one dominant or one recessive)
define genotype
the genes present for a trait
define phenotype
- the visible characteristic
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 a certain allele
give two examples of inherited disorders:
- is it dominant or recessive
- describe what it is
- Polydactyly - caused by a dominant alleles - having extra fingers or toes
- Cystic fibrosis caused by a recessive allele - disorder of cell membranes
how are embryos screened for inherited disorders?
- during IVF , one cell is removed ( from an 8-inch 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
give three ethical issues concerning embryo screening?
- it could lead to beliefs in society that being disabled or having a disorder is associated with inferiority
- the destruction of embryos with inherited disorders is seen as murder and against the idea of sanctity of life
- it could be viewed as ‘’ designer babies’’ as it may be for parents convenience rather than the child’s wellbeing
what are the economic issues concerning embryo screening?
- consideration of costs of treatment and medication of the child with the inherited disorder
- financial support may be needed
give two social issues concerning embryo screening?
- if embryo has an inherited disorder and is discarded off, this can prevent a child and its parents from potential suffering
- social care for children with inherited disorders may need to be considered
define gene therapy
- the insertion of a normal allele into the cells of a person with an inherited disorder to functionally replace the faulty allele
give two ethical issues concerning gene therapy
- some people believe that it is playing god
- the introduced genes could enter sex cells and so be passed to future generations
what are sex chromosomes and examples..
a pair of chromosomes that determine sex:
- males have an X and a Y chromosmes
- 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 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
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what is variation?
- differences in the characteristics of individuals in a population
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
give two things which create genetic variation in a species?
- spontaneous mutations
- sexual reproduction
what is a mutation
- a random change to the base sequence in DNA which result in genetic variants
- they occur continuously
state the three types of gene mutation
- insertion
- deletion
- substitution
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
define 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
Describe Darwin’s theory of
evolution by natural selection
- There is a range of natural variation within a species due to mutation
- due to this, some organisms will be better suited to that environment
- These individuals are more likely to
survive and breed - The favourable alleles will be passed onto their offspring
- This process is repeated over many
generations
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 four main steps involved in selective breeding.
- identify a desired characteristics 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 4 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
give the main advantage of selective breeding and 4 examples
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 four disadvantages of selective breeding
- reduction in the gene pool
- 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
- enables the formation of an organism with beneficial characteristics
give two examples 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
Describe the 3 benefits of genetic engineering
- increased crop yields for growing population e.g. herbicide
- useful in medicine eg insulin producing bacteria
- GM crops produce scarce resources eg GM golden rice
Describe the 4 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
- late onset health problems in GM animals
- GM seeds are expensive. LEDCs may be unable to afford them
what is the name for the crops that have had their genes modified?
- GM crops - genetically modified crops
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
give three 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
give three 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
- use restriction enzymes to isolate the required gene
- This gene is inserted into a DNA vector, usually a bacterial plasmid or virus.
- the vector is used to insert the gene into the required cells
• genes is then transferred to the cells of animals at an early stage so they can develop the desired characteristic
what is a vector ( in genetic engineering)
- a structure that delivers the desired gene into the recipient cell e.g. plasmids. viruses
State four benefits of genetic engineering.
- Improved growth rates
- Increased yield
- Increased food quality
- enzymes as medicine
give two ways plants can be cloned? (2)
- taking plant cuttings
- tissue culture
define 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
give the 4 advantages of growing plants by tissue culture (4)
- fast and simple process
- enables the growth of many plant clones with the same desirable characteristics
- useful in the preservation of rare and endangered plant species
give three disadvantages of growing plants by using tissue cultures
- 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 cutting
method to clone plants
- a branch is cut off from parent plant
- the lower leaves of the branch are removed and the stem is planted
- rooting powder is used to encourage growth
- a polythene 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 are 2 methods to
clone animals?
- embryo transplant and adult cell cloning
describe the embryo transplant to clone animals
- Sperm is taken and is used to artificially fertilise an egg cell
- Embryo forms
- The embryo is split apart into single cells before they become specialised.
- The single cells divide by mitosis to form genetically identical embryos
- Identical embryos are then placed into host mothers
- Genetically identical offspring form
Describe the adult cell
cloning method to clone animals
- A nucleus is removed from an unfertilised egg cell
- The nucleus from an adult body cell is inserted into the empty egg cell
- An electric shock stimulates the egg cell to form an embryo (which contains the same genetic information as the adult cell)
- when the embryo is a ball of cells , it is inserted into the uterus of a surrogate mother
why was Darwin’s theory of evolution not accepted initally?
- His theory challenged the idea that
God made all the animals and plants on
Earth - There was insufficient evidence at the
time the theory was published - The mechanism of inheritance and
variation was not known until 50 years
after the book was published
What was Lamarck’s theory
of evolution
● He thought that if a characteristic was
used a lot by an organism, the
characteristic will develop over its
lifetime and pass this on to their
offspring
define speciation
The formation of a new and distinct species
over the course of evolution by natural
selection
define ‘ 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 (6)
- There is a geographical barrier
between the population of the same
species - There will be genetic variation within
each population - The environments will be different on either side of the barrier
- Natural selection occurs – those suited to their environments will survive and
breed - The favourable genes are passed onto their offspring
- This happens over many generations
resulting in different species which are unable to interbreed to produce fertile offspring
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
Suggest 3 reasons why Mendel’s work on genetics was not initially fully accepted
- Scientists at the time did not know
about genes or chromosomes - His work was published in an obscure
journal - His work was not understood by other
scientists
state two kinds of evidence used to show evolution
- fossils
- antibiotic resistance in bacteria
give three ways fossils are formed
- parts of organisms that have not decayed due to conditions needed for decay being absent
- bones that have been replaced by minerals as they decayed
- 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
what are fossils?
Remains of organisms from millions of years
ago that are found preserved (in rocks, ice etc.)
Describe the five steps of fossilisation by
mineralisation.
- Organism dies and falls to the ground
- Flesh decays, leaving the skeleton behind
- Bones are covered in sand/soil
- Bones become mineralised and turns into rock (fossil);
- Rock with fossil emerges due to geological
movement (e.g. earthquake) and erosion occurs to reveal fossil
how do fossils act as evidence for evolution?
- scientists can identify the ages of the fossils and use the to show how organisms change over time
what do branches in evolutionary trees indicate ?
- where speciation has occurred
define extinction
- where there are no individuals of a species still alive
state 5 factors that may lead to extinctions
- new disease
- predation
- competition
- changes to the environment
- catastrophic events
What are the three different types of
fossils that can be formed?
- Mineralised skeleton
- un-decayed due to trapped in ice or amber
- Preserved traces of organisms (eg. footprints, leaves)
Give 4 reasons why the fossil record is
incomplete.
- Many earliest life forms are soft-bodied
- Most organisms did not become fossilised
- Most early fossils were destroyed by geological activity
- Many fossils are not yet found
What causes mass extinction? Suggest two
examples of this cause.
Single catastrophic event that also affects
climate over a long period (eg. asteroid
collision, volcanic eruption)
. Suggest a chain of events initiated by an
asteroid collision that could lead to the
extinction of dinosaurs.
- Asteroid impact causes huge fires and
earthquakes and volcanic eruptions - dust/ash cloud covers atmosphere leads to less sunlight
- this reaches the Earth surface so temp drop
massively + plants die - leads to a loss of food source led to other animals’ extinction
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 reduce the rate of development of antibiotic resistant bacteria?
- refrain from inappropriately prescribing antibiotics e.g. viral diseases
- patients should complete the prescribed course of antibiotics
- restrict agricultural uses of antibiotics
Why is it difficult to develop new
antibiotics to combat the appearance of
new antibiotic-resistant strains of bacteria?
The development of new antibiotics is
expensive and slow (won’t be able to keep up
give the 7 classes of organisms as determined by Carl Linnaeus ?
- kingdom
- phylum
- class
- order
- family
- genus
- species
what 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
give two reasons why new classification models proposed ?
- developments in microscopy allowed better examination of internal structures
- improvement in understanding in biochemical processes
state the three domains/
- archaea
- eukarya
- prokarya
which organisms belong in the domain Archea?
- bacteria usually living in extreme environments
which organisms belong in the domain bacteria?
bacteria
which 4 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 aspects of knowledge would be
considered when suggesting evolutionary
relationships?
Similarities and differences in physical
structures, genetics and biochemistry
what language does the binomial naming system use?
- latin
Why do we use the binomial naming
system?
- Every organisms’ names would vary in different languages, but Latin is considered to be the old common language in which everyone can use/understand
