Year 11 Term 2 Flashcards
What does genetic engineering involve
Changing the genetic material of an organism
What is the first step of genetic engineering
Insulin gene is cut out of DNA by an enzyme and plasmid is taken out of bacterium and split open by a restriction enzyme
What’s a restriction enzyme
They recognise specific sequences of DNA and cut the DNA at these points. The cut leaves one of the DNA strands with unpaired bases, this is called a sticky end
What is the second step of genetic enginerring
The insulin gene is inserted into plasmid by another enzyme, then this plasmid is taken up by the bacterium. The bacteria then multiplies many times, the insulin gene is switched on and the insulin is harvested
What are other examples of genetic engineering
Genes can be cut out of the DNA of one plant and inserted into rice genes, enzymes are still used in this process
In animals, plants and microbes, when does genetic modification usually take place
Genes are often transferred at early stage of development so that the organism develops with the desired characteristics
GM of golden rice
Genes in the pathway for better carotene production are obtained and introduced to the white rice genome, resulting in golden rice which increases the vitamin A content almost 25 fold
Arguments for GM (genetically modified) crops
Higher crop yields Can be resistant to herbicides Reduces pesticide use Safe for human consumption Preserves habitats as less land needed to grow crops Better shelf life
Arguments against GM cops
Unknown long term health risks
Could affect wildlife as killing weeds
Increasing yields means a distribution problem
GM crops are often infertile
What is another name for meiosis
Reduction division
Where is the only place meiosis occurs
Only in the cells of the reproductive organs and produces gametes (sex cells) in the ovaries and testes or then anther and ovule of a plant
What does haploid mean
Half the number of chromosomes
What does diploid mean
Full sets of chromosomes e.g. 46 or 23 pairs
Why do gametes only have one copy of each chromosome
So that when gametes fuse at fertilisation, the zygote has the normal amount of chromosomes. The zygote then divides by mitosis to produce more cells that differentiate as the embryo develops
What happens during meiosis
Chromosomes replicate then shorten and thicken. The pairs line up at centre of cell and spindles attach these pairs separate into 2 new cells and nucleus reforms, spindles attach to the duplicates of chromosomes and are pulled apart into separate cells
What is left at the end of meiosis
4 new cells have formed each having 2 chromosomes (23) they are haploid cells and each one contains different genetic material to the others
What is asexual reproduction
Only 1 parent, no fusion of gametes so offspring genetically identical, happens by mitosis, only genetic variation is random mutations
What are the several types of asexual reproduction
Binary fission (bacteria)
Production of spores (fungi)
Strawberry (runners)
Potato (tuber)
What is sexual reproduction
Mixing of genetic info from 2 organisms, offspring genetically different to parents, male and female gametes produced by meiosis fuse, nuclei of cells are haploid and unite at fertilisation forming diploid zygote
Ads and Disads of sexual reproduction
Increases chance of survival if circumstances change, there is genetic variation however a partner needs to be found
Ads and Disads of asexual reproduction
Only needs 1 parent, no time/energy wasted finding a mate, produces large amount rapidly however susceptible to disease and no genetic variation
Malaria sexual and asexual reproduction
Malaria caused by parasite that’s spread by mosquitoes. The parasite reproduces sexually when it’s in the mosquito and asexually when it’s in the human host
Fungus sexual and asexual reproduction
These fungus species release spores which can become new fungi when land in a suitable place. a.s produced spores form genetically identical fungi to parent fungus. s produced spores introduce variation and produced in response to a change in the environment, increasing the chance of the fungi surviving the change
What does DNA stand for
Deoxyribonucleic acid
What is DNA made up from
Is a polymer made from 4 different nucleotides, each nucleotide consists of a common sugar and phosphate group with 1 of 4 different bases attached to the sugar, A, T, C, G
Where is DNA found
In chromosomes
What is a gene
A small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids to make a specific protein
What is the sequence of 3 bases
It’s the code for a particular amino acid. The order of the bases controls the order in which amino acids are assembled to produce a particular protein
Double helix shape of DNA
The 2 sides of the ladder are made of alternating sugar molecules and phosphate groups
The rungs of the ladder are made of chemicals called bases, each base is attached to sugar molecule of the side (or backbone) of the DNA
How many types of amino acids are there
There are 20 amino acids but can be put together in many different orders to make thousands of different proteins
What is the genome of an organism
It’s the entire genetic material of that organism
What has studying the whole human genome allowed us to do
The search for genes linked to different types of disease
The understanding and treatment of inherited disorders
Tracing human migration patterns from the past
How are proteins formed
The sequences of bases from DNA is copied to form a messenger molecule which leaves the nucleus and moves to ribosome in the cytoplasm of the cell. Carrier molecules bring specific amino acids to the ribosome and attach to the messenger molecule in order determined by sequence of bases. Amino acids are formed together to form protein
Hair protein
Keratin, a fibrous structural protein
Muscle protein
Actin, forms filaments in muscles
What is a muation
A random change in an organisms DNA
When do mutations occur
All the time often due to a mistake in copying DNA before the cell divides
Are mutations beneficial
Yes, they can be and are one of the driving forces of evolution
How can the chance of mutation be increased
By exposure to some chemicals or radiation
How do mutations change the sequence of DNA bases in a gene
One of the amino acids may be substituted with another which may change intermolecular forces between amino acids so the protein may change shape and if it’s an enzyme then enzyme and substrate won’t fit so will lose function
Non-coding DNA
Not all parts of DNA code for proteins. Non-coding DNA can switch genes on and off, so variation in these areas if DNA may affect how genes are expressed
Genes and charcteristics
Genes you inherit from parents control your characteristics, most of which are due to multiple genes interacting rather than a single gene but some are controlled by single gene such as fur colour in mice
What’s an allele
A different form of a particular gene
Why do other cells (not gametes) have 2 alleles, one on each chromosome of a pair
Because we inherit half of our alleles from our mother (in the egg) and half from our father (in the sperm)
Dominant
An allele that is always expressed in the phenotype, even when only copy is present. It;s represented by a capital letter
Homozygous
When an organism has two alleles for a particular gene that are the same e.g. AA or aa
Genotype
The alleles (letters) present for a particular gene in a organism
Chromosome
Thread-like structure in the cell nucleus made of a molecule of DNA which carried genes
Recessive
An allele that’s only expressed in the phenotype if two copies are present (and therefore no dominant allele present) It’s represented by a lowercase letter
Hetrozygous
When an organism has two alleles for a particular gene that are different e.g. Aa
Phenotype
That characteristics that is shown or expressed
What do genetic diagrams allow you to do
Allow you to see how certain characteristics are inherited. You cross (breed together) two parents
What is polydactyly
Inherited disorder where born with extra fingers or toes
not life-threatening
What causes polydactyly
Caused by dominant allele so can be inherited if just one parent carries defective allele. The parent with the allele will also have conditions since it’s dominant
What is cystic fibrosis
Inherited disorder of cell membranes, results in body producing lots of thick mucus in air passages of lungs (makes breathing difficult) and in the pancreas
What causes cystic fibrosis
Caused by recessive allele which is carried in 1/25 people. As it’s recessive, people who only one copy don’t have the disorder, known as carriers but don’t have syptoms
Treatments for cystic fibrosis
Physiotherapy and antibiotics (to keep lungs clear), taking enzymes to replace ones made in pancreas
Currently no cure
What is embryo screening
A way of detecting inherited genetic disorders such as cystic fibrosis in embryos
What is pre-implantation genetic diagnosis (PGD)
During IVF a cell is removed from embryo and genes analysed so only embryos with healthy alleles are implanted. Faulty ones are destroyed
What is chorionic villus sampling (CVS)
A sample of cells is taken from placenta at 10-13 weeks and genes analysed. If embryo has an inherited disorder, parents decide whether to terminate pregnancy
Arguments for screening
Helps to stop people from suffering from inherited disorders which reduces healthcare costs
Gives parent the choice to terminate the pregnancy
Arguments against screening
May lead to people choosing desired characteristics
Implies those with disorders are ‘undesirables so increases prejudice
Rejected embryos are destroyed which some view as unethical
Very expensive to screen embryos
Sex determination
23rd pair of chromosomes are the sex chromosomes which determine your sex
Male sex chromosomes
XY
Female sex chromosomes
XX
What did Mendel cross in the first cross and what were the results
Crossed tall pea plant and dwarf pea plant which resulted in all tall pea plants
What did Mendel cross in the second cross and what were the results
Crossed 2 pea plants from the 1st offspring which resulted in 3 tall pea plants and 1 small pea plant
How did Mendel explain the results
Characteristics in plants are determined by hereditary units
H.U are passed on to offspring unchanged from both parents, one unit from each prent
H.U can be dominant or recessive
Why wasn’t his explanation accepted by other scientists
The peers lacked any background knowledge
They didn’t know about genes, chromosomes and DNA
When were Mendel’s theories taken seriously
early 20th century when scientists realised the similarities between the way that chromosomes and Mendel’s units acted
Definition of species
A group of living organisms that are able to interbreed to produce fertile offspring
What is variation
The difference in the characteristics of individuals in a population
What may cause variation
The genes they have inherited
The condition in which they have developed
A combination of genes and the environment
What are mutations
They are changes to the sequence of bases in DNA
What effect do mutations have on an organisms phenotype
Most have no effect on the phenotype, some have a small affect and alter the characteristics slightly, very rarely do mutations result in a new phenotype
Definition of evolution
A change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species
How does natural selection work
Variation caused by mutation, so the variant with the advantage will survive and breed, passing on the advantage genes to the next generation
Darwin’s theory of evolution
He believed in natural selection however was only gradually accepted because it didn’t mention any mutations, genes or DNA he believed the individuals with characteristics most suited to the environment passed them on
What was Lamarck’s theory
The evolution of animals was caused by the inheritance of acquired characteristics, based on the idea that changes occur in an organisms lifetime can be inherited
Creationism
Living things were created separately, they did not evolve
Theory of intelligent design
Life is too complex to have evolved so must have been put together by a higher being
Religion
Some people may not accept scientific theories because they believe in a creator
How are fossils evidence of evolution
Fossils show changes over time and some features are similar to present day
New species arise as a result of:
Isolation
Genetic variation
Natural selection
Speciation
What is speciation
The development of a new species
Occurs when populations of the same species become so different they can no longer successfully interbreed to produce fertile offspring
How does bacteria develop resistance to antibiotics by natural selection
Mutations of bacterial pathogens produce new antibiotic resistant strains
Antibiotics kill individual pathogens of the non-resistant strain
Individual resistant pathogens survive and reproduce so pop of resistant strain increases
resistant strain will spread
