GCSE Flashcards
Chromosome differences in cells
In normal body cells there are 46 chromosomes which form 23 pairs stored in a nucleus .
In a sex cell there are 23 chromosomes not paired up
Difference between meiosis and mitosis
Mitosis usually produces normal body cells that are exact copies of the original cell
Meiosis only occurs in sex cells . Each sex cell is different from the other
Advantages and disadvantages of sexual reproduction
Produces a variation of offspring . This can give a species a particular trait which through natural selection will be found in other members of the species
Selective breeding can be used to produce certain temperaments or increase crop yields.
However the process is a lot slower and requires more energy as the female must carry the offspring for a long amount of time
Pros and cons of asexual reprodcution
Much faster process as only one organism is required. Less energy is use .
Because there is no variation in the offspring . If a disease spread that killed of the species of organism there would be no organism that would have a genetic mutation allowing them to be resistant ti the strain as they are a complete copy of the parent
What organisms use both forms of reproduction?
In a human host the malaria parasite produces asexually however when in a vector mosquito the parasite reproduces sexually.
Fungi can produce asexually by releasing spores but can also sexually reproduce . This provides variation in offspring.
All flowering plants produce sexually by forming seeds. Also they can release runners that sprout out forming a copy of the plant
DNA
Chromosomes contain the molecule DNA
DNA is a genetic material .
DNA consists of 2 strands each one is a polymer and they wrap around one another forming a double helix shape.
What is a gene ?
A gene is a small section of DNA on a chromosome.
Each gene codes for a certain sequence of amino acids which will produce a specific protein.
What is a genome
The genome is the entire genetic material of one organism.
The entire human genome has been study. This allows scientists to identify genes associated with disease
Structure of DNA
It is a polymer of molecules called nucleotides
Each nucleotide consists of one sugar one phosphate and a base
There are 4 bases . A links with T and C links with G
Protein synthesis
DNA unwinds and unzips in the nucleus
MRNA molecule takes a copy of the base sequence of that gene
The MRNA take that copy and travel to the ribosome.
The ribosome reads the bases in groups of 3 called codons.
Each codon read causes an amino acid to be produced
Once all the bases are read a chain of amino acids will have been formed creating a specific protein
Mutations
A change to a base is called a mutations
Most mutations do no harm
However if the base sequence is changed than different amino acids will be produce impacting the protein as it’s active site may have morphed making the enzyme useless
Non coding DNA
Chromosomes contain regions of non coding DNA . It is believed that these regions decide which characteristics are expressed in the organism by switching genes on and off. They tell genes when to produce proteins , if a mutation occurs in the non coding DNA it may cause the genes to become active when they should off. This uncontrollable production of materials can cause cancer
What are alleles
A different form of a gene
If a person has the same 2 copies of an allele then they are a homozygous . If they have different pairs of alleles they are heterozygous
What is cystic fibrosis ?
A disorder effecting the cell membrane .
Selective breeding
Take animals with desired characteristic
Breed them until one or more offspring show this trait
Breed offspring
Repeat process until 1 litter all bare that trait
Genetic engineering
Identify gene you want Use enzyme to isolate gene Transfer gene into a plasmid Place plasmid into organism Plasmid will replicate . Each replica contains this desired gene
Cloning plants
Cut a pieces of a plant .place them in rooting powder . These cuttings will grow into exact copies of the original plant .
However if you want to produce a large number of clones. Divide plant into lots of pieces. Incubate these pieces with plant hormones allowing them to fully develop
Cloning animals
Embryo transplant-
Fuse egg and sperm cell
Allow egg cell to develop into a clump of cells
Split clump of cells into 2 or more parts
Transplant the parts into host mothers
The parts will grow in different wombs but will be complete copies of kne another
Or
Adult cell cloning-
Remove any cell from an adult organism
Select an egg cell and remove nucleus . Replace the nucleus with the animal cell
Stimulate the division of the egg cell with a current
Once a clump of cells place into a surrogate
The offspring produced will be am exact copy of the animal that had it’s cell removed
What did lamarck state
That animals across a lifetime will adopt characteristics that will pass down to it’s offspring directly
Why did it take a long time for Darwins theory to be accepted ?
It contradicted with religious belief . Also he had little evidence to prove his theory as genes had not been discovered yet.
Mendel and genetics
Carried out thousands of experiments on pea plants
He found out characteristics did not blend with each other. For example the number of peas produced did not impact the size of the flower.
He stated the characteristics were inherited and that units were responsible for this , genes had not been discovered at the time.
He also discovered that many traits would not appear fir generations at a time . We now realise that these traits where due to recessives genes.
Classification
Carl linneaus classified species into different catergories He divided them into plant , animal He divided those 2 categories into smaller categories . Kingdom Phylum Class Order Family Genus Species
Homeostasis
The regulation of internal conditions of an organism to maintain optimum functionality in response to external or internal changes.
Action
Stimuli Receptors Sensory neuron CNS Relay neuron Motor neuron Effector Response
