Inheritance, Variation and Evolution Flashcards
Paper 2 - B6
What is the purpose of meiosis?
Production of gametes (sex cells)
How is mitosis different from meiosis?
Meiosis leads to production of 4 non-identical cells, mitosis leads to production of 2 identical cells
Name the gametes (sex cells) in a) flowering plants b) animals
a) pollen and egg cells b) sperm and egg
Why is sexual reproduction important?
It involves mixing of gametes which leads to variation
What is asexual reproduction?
Reproduction involving only one parent and no fusion of gametes
What type of offspring are produced in asexual reproduction?
Genetically identical organisms (clones)
What does meiosis do to the number of chromosomes in gametes?
It halves the number
Gametes have half the number of chromosomes as body cells. In what process is the full number restored?
Fertilisation
What happens in the nucleus of a cell before meiosis?
Copies of the genetic information (DNA, chromosomes) are made
How many gametes are produced in meiosis?
Four
What type of cell division occurs AFTER fertilisation to lead to an embryo?
Mitosis
What happens to the cells in an embryo to eventually cause organs etc. to develop?
Cells continue to multiply by mitosis and then they DIFFERENTIATE
(Triple only) What is the advantage of sexual reproduction
Produces variation in offspring giving an advantage if the environment changes
(Triple only) Give 4 advantages of asexual reproduction
Only 1 parent needed; more time/energy efficient as don’t need to find a mate; faster than sexual reproduction; many identical offspring produced when conditions are
favourable
(Triple only) Why is genetic variation an advantage?
Natural selection can occur if the environment changes
(Triple only) Name 3 organisms that can reproduce by both sexual and asexual reproduction
Malarial parasites; fungi; plants e.g. daffodils, strawberry plants
(Triple only) Which type of reproduction (asexual or sexual) of malarial parasites occurs in the human host and which occurs in the mosquito?
Asexual in human host, sexual in mosquito
What is the structure of DNA?
Double helix
What is the genome?
The entire genetic material of an organism
What is DNA?
A polymer made up of two strands in a double helix
What structures contain DNA?
Chromosomes
What is a gene?
A small section of DNA on a chromosome
What does a gene code for?
A particular sequence of amino acids to make a specific protein
Give 3 reasons why understanding the human genome is important
Search for genes linked to different diseases; understanding & treatment of inherited disorders; use in tracing human migration patterns from the past
(Triple only) What units make up DNA?
Nucleotides
(Triple only) What are the 3 components of a nucleotide in DNA?
Sugar, phosphate group, one of 4 bases
(Triple only) Name the 4 bases in DNA and say how they pair up
A, T, C, G; A pairs with T; C pairs with G
(Triple only) How many bases are the code for one amino acid?
Three
(Triple only) In DNA, what does the order of bases control?
The order in which amino acids are assembled to make a particular protein
(Triple only) Where are proteins synthesised?
On ribosomes
(Triple only) What happens in protein synthesis?
A copy of the DNA (a template called mRNA) attaches to a ribosome which reads the bases in threes. Carrier molecules (tRNA) bring the correct amino acids to add to the growing protein chain
(Triple only) What is a mutation and how might it affect a protein?
A change in DNA structure (different bases) which changes the shape/function of the protein produced
(Triple only) What happens to a protein to give it a unique function?
It folds up into a unique shape
(Triple only) List three types of proteins
Enzymes, hormones, structural
(Triple only) How might a mutation affect an enzyme?
It alters the shape of the active site so the substrate cannot bind
(Triple only) Give one role of the non-coding parts of DNA
Switch genes on and off
(Triple only) What effect might a mutation have to a non-coding part of DNA
It might affect how genes are expressed
What is the effect of most mutations?
Most have no effect, some may be harmful or beneficial
What are alleles?
Different forms of a gene
In genetics, what does dominant mean?
Only one copy of an allele is needed to produce a characteristic (always expressed)
In genetics, what does recessive mean?
Two copies of an allele are needed to produce a characteristic (only expressed if no dominant allele is present)
What is the genotype?
Pair of alleles for a characteristic
What is the phenotype?
The characteristic caused by a particular
pair of alleles
What does homozygous mean?
Two alleles of the same type for a characteristic (i.e. both dominant or both recessive)
What does heterozygous mean?
A genotype with one dominant and one recessive allele
Give an example of a characteristic in humans controlled by a single gene
Red-green colour blindness
Name the grid used to show the results of a genetic cross
Punnett square
Why do most characteristics have many different possible phenotypes (e.g. lots of different hair colours and types)?
They are caused by multiple genes, not just one
Name an inherited condition caused by a recessive allele
Cystic fibrosis
Name an inherited condition caused by a dominant allele and affecting the hands and feet
Polydactyly
How can embryo screening be used to prevent genetic disorders
Following IVF, embryos can be tested for genetic disorders before being implanted back into the mother
What is the ethical issue relating to embryo screening?
Deciding what counts as a ‘genetic disorder’ (level of severity etc.) and fact that embryo may then be destroyed
How many pairs of chromosomes are in ordinary body cells?
23 pairs
What pair of sex chromosomes are found in the nucleus of male body cells?
XY
What pair of sex chromosomes are found in the nucleus of female body cells?
XX
Aside from genes, what else can affect the overall phenotype of an organism?
Interaction with the environment
How does new genetic variation arise?
Mutations
What is evolution?
A change in the inherited characteristics of a population over time through natural selection
When did the first life forms on earth develop?
Over 3 billion years ago
What is natural selection?
When organisms with the most favourable genetic variants survive, reproduce and pass on their alleles, meaning that these increase in the population
When is a new species formed?
When two populations of one species become so different in phenotype that they can no longer interbreed to produce fertile offspring
What is a species?
Organisms with similar characteristics that can interbreed to produce fertile offspring
What is selective breeding?
When humans breed plants or animals for particular genetic characteristics
How is selective breeding carried out?
Choose parents with desired characteristics, breed together, select offspring and repeat over many generations
List 4 characteristics which might be chosen for selective breeding
Disease resistance in food crops; more meat or milk in animals; domestic dogs with gentle nature; large or unusual flowers
What is the main disadvantage of selective breeding
Inbreeding where some breeds are particularly prone to disease or inherited defects
What is genetic engineering?
Modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic
Give two characteristics produced by genetic engineering in plants
Disease resistance; bigger, better fruits
What useful product is now produced by certain bacteria as a result of genetic engineering
Human insulin
Give three characteristics of genetically modified crops
Resistance to insect attack; resistance to herbicides; increased yield
Give two concerns relating to GM crops
Effects of wild populations of flowers and insects; effects on human health haven’t been fully explored
How could genetic modification be used in humans?
To overcome certain inherited disorders (gene therapy)
In genetic engineering, what is used to isolate and remove the required gene?
Enzymes
In genetic engineering, what is usually used as a vector to transfer the gene into the new organism?
A plasmid or a virus
In genetic engineering, what is the purpose of the vector?
To transfer the gene into the required cells
Why is genetic engineering usually done during an early stage of the organism’s development?
So that the organism develops with the desired characteristic
(Triple only) What is tissue culture?
Using small groups of cells from part of a plant to grow identical new plants
(Triple only) Give two methods of cloning plants
Tissue culture; taking cuttings
(Triple only) How is cloning carried out in animals?
Embryo transplants; nuclear transfer (adult cell cloning)
(Triple only) How are embryo transplants carried out in order to clone an animal?
Cells in an embryo are split apart before they become specialised, then the embryos are transplanted into host mothers.
(Triple only) How can cloning be carried out using adult cells?
Nucleus removed from unfertilised egg cell and replaced with nucleus from adult body cell. Electric shock given, so cell divides to form an embryo, then inserted back into womb of adult female
(Triple only) Who came up with the theory of natural selection and how?
Charles Darwin, on a round the world expedition and based on observations of fossils, geology and experimentation
(Triple only) Describe the stages in evolution by natural selection
Genetic variation, survival of the fittest, breeding and passing on characteristics
(Triple only) Name Darwin’s book and the date of publication
On the Origin of Species, 1859
(Triple only) Give 3 reasons why Darwin’s theory was only gradually accepted
It challenged ideas about God making all the animals/plants; insufficient evidence at the time; mechanism of inheritance (genes) was not known for another 50 years after publication
(Triple only) Who came up with an alternative theory to Charles Darwin?
Jean-Baptiste Lamarck
(Triple only) How did Lamarck’s theory differ from Darwin’s?
He proposed that characteristics developed during an organism’s lifetime could be passed on (Darwin said only characteristics you were born with)
(Triple only) Who proposed natural selection independently to Darwin but also published papers with him?
Alfred Russell Wallace
(Triple only) Aside from evolutionary theory, what else did Alfred Russell Wallace work on?
Warning colouration in animals
(Triple only) What is speciation?
Development of a new species through natural selection occurring differently in isolated populations
(Triple only) What did Mendel do, and how did it influence the theory of evolution?
Experiments on plant breeding; Basic ideas about ‘units’ of inheritance (later known as genes)
Give two pieces of evidence for evolution
Fossils; antibiotic resistance in bacteria
How do fossils provide evidence of evolution?
Show gradual changes in organisms over time
How does antibiotic resistance provide evidence for evolution?
It shows how an organism can change when the environment changes
What are fossils?
Remains of organisms from millions of years ago which are found in rocks
How do fossils form (three ways)?
Parts of organisms don’t decay; parts of organisms are replaced with minerals as they decay; preserved footprints etc.
Why don’t all organisms form fossils?
Many organisms are soft bodied and don’t form fossils easily; some are destroyed by geological activity
What is extinction?
When there are no individuals of a species left on earth
List some factors that may contribute to extinction of a species
Climate change; hunting; disease; new predators etc.
What is MRSA?
A particular microorganism that is resistant to antibiotics
How can we reduce antibiotic resistance?
Only prescribe antibiotics when necessary; patients must complete the course; reduce agricultural use of antibiotics
Why is antibiotic resistance a concern?
People are not immune to the bacteria but it cannot be treated with antibiotics; Development of new antibiotics is costly and slow - can’t keep up with emergence of resistant strains
Who developed the first system for classification of organisms?
Carl Linnaeus
List the levels in the classification system proposed by Carl Linnaeus
Kingdom, phylum, class, order, family, genus, species
(King Philip Came Over For Good Soup)
What are the two parts of an organism’s binomial name?
Genus and species
Give two reasons why our ideas about classification have changed since Carl Linnaeus first proposed his system
Development of microscopes advances knowledge of structures inside cells; understanding of biochemical processes progressed
Who proposed the ‘Three Domain system’ of classification?
Carl Woese
What are the three groups of the ‘three domain system’ of classification?
Archaea, bacteria, eukaryota
What are the archaea (in the ‘three domains system’ of classification)?
Primitive bacteria usually living in extreme environments
How can we show in a visual way how organisms are related?
Evolutionary trees
What information is needed to construct an evolutionary tree?
Classification data for living organisms and fossil data for extinct organisms
