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What is an allele?
When a gene can exist in more then one form
How many chromosomes does a human have and what is the pair called?
46 chromosomes which are stored in matching pairs called homologous pairs
What is an intron
Sections of code that don't work such as multiple repeats which are non-functional
What is a proteome?
The full range of proteins that the cell is able to produce
What does a base triplet code for?
An amino acid
-base sequence of a gene will determine the sequence of amino acids
What is an allele?
When a gene can exist in more then one form
What is a gene?
Sections of DNA that contain the coded information for making polypeptides
they occupy a fixed position (locus) on a DNA strand
the coded information is in the form of a specific sequence of bases
What is a genome?
A complete set of genes in a cell
what is a singlet code
Where one nucleotide codes for one amino acid could only provide four different nucleotides
How mant combinations of nucleotides can be had from a triplet codes
64
What is a triplet code
The smallest coding unit that can accommodate 20 amino acids that make up a variety of proteins
What is the genetic code
DNA and RNA molecules carry genetic information in cells
It is non-overlapping
It is universal
It is degenerate
What does degenerative mean
More possible combinations of triplet codons than there are amino acids eg there are 64 codons but 20 amino acids
What is a silent mutation
Occurs when the substitution of a base still codes for the same amino acid as the original base as the genetic code is degenerate
What is a nonsense mutation
Occurs when a substitution of a base occurs leading to a premature stop codon being coded for
This would lead to the premature end to the synthesis of a polypeptide
How manu stop codons are there
3
What can nonsense mutations lead to
Thalassemia
It is a autosomal recessive blood disease
This results in a reduced rate or so synthesis of one of globin chains that make up haemoglobin
This causes anaemia
What is mis-sense mutation
A mis-sense mutation occurs when a change in base leads to a different amino acid being coded for
The polypeptide will have a single amino acid that is different
What is an effect of mis-sense mutation
If the role of the amino acid was involved in the formation of bonds, the enzyme will no longer have a specific structure and wont be able to catalyse a reaction
What disease can cause mis-sense mutation and describe the disease
Sickle cell disease
Mutation in the haemoglobin gene
Describe the deletion of bases
When a nucleotide is lost from the DNA sequence
This leads to codons not being read properly
And the sequence being shortened
What disease is caused by deletion
Tay-sachs disease
Recessive disease
Describe addition of bases
When a nucleotide is added to the DNA sequence
Causes of mutations
Can occur by mistake during DNA replication
What is a mutagenic agent
A physical or chemical agent that increases the frequency of mutations
What is asexual reproduction
New organism is genetically identical to the parent
What is sexual reproduction
Meosis produced haploid gametes
Gamtes’s fuse at fertilisation to form a diploid zygote
Genetic variation in offspring
What is the difference between haploid and diploid
Haploid (n) = half number of chromosomes
Diploid (2n) =full set of chromosomes
what is meiosis
Meiosis is a reduction division
results in daughter cells having half the original number of chromosomes
These daughter cells are called sexual reproduction
Can be used by a sexual reproduction
What are the 2 divisions in meiosis
Meoisis l
Meiosis ll
What happens at early prophase l
Chromosomes condense and become visible as threads
Homologous chromosomes join to pairs called bivalent
A chromatid of one chromosome in a bivalent can cross a chromatid of the other to form a chiasma
What happens at late prophase l
Chromosomes have condensed enough to become visible
What happens at metaphase l
Nuclear envelope disappears
Spindle fibers are formed and attatch to centromeres
What happens at anaphase l
The homologous chromosomes of each bivalent separate
They are pulled to opposite poles by micro tubules
THIS STEP IS WHERE CHROMOSOMES HALF
What happens at telophase l
Chromosomes reach opposite poles and may decondnse to form 2 nuclei
What happens at cytokenisis l
The plasma membrane folds inwards to form 2 cells
The centrioles divide
What happens at prophase ll
Chromosomes condense
Spindle fibers develop
What happens at metaphase ll
Nuclear envelope disappears
Chromosomes are pulled to the equator
Difference to metaphase l as they are lined up sing,e file rather than pairs
What happens at anaphase ll
Centromeres divide so each chromatid is now a chromosome. These chromosomes move to opposite poles
What happens at telophase ll
Chromosomes reach poles
They nuclear envelope reforms around haploid nuclei
Cytokinesis ll
Original cell has produced four cells
Each cell has one chrimatid
What is a locus
Position of a gene on a chromosome
How does genetic variation happen
Through sexual reproduction which occurs by production of haploid gametes
What processes are responsible for genetic variation
Crossing over
Random assortment of chromatids
Random fertillisation
Independent assortment of chromosomes
Chromosome mutations
Why are organisms different from one another
Mutations
Random fusion of gametes
Independent segregation
Crossing over
What can meoisis lead to
Genetic variation among offspring which may lead to genetic variation
What do all members of the same species have
The same genes
What is genetic diversity
The total number of different alleles in a population or species
How does genetic diversity enable natural selection
Increased genetic diversity increases the probability that some individual will possess a characteristic that suits it to the new environmental conditions
What two things will populations with high genetic diversity have
Lots of different alleles which leads to different phenotypes
why is it good for a population to have a high genetic diversity
They can adapt to change in the environment
How can new alleles be brought into a population
Through migration
Descirbe how migration brings new alleles
A new population of the same species may enter an area and interbreed with original population
This will bring new and existing alleles into population
This is called gene flow
What is a genetic bottleneck
When the size of a population is dramatically reduced
What happens to the gene pool from genetic bottlenecks
Gene pool gets smaller
What is the founder effect
when a few members of a population leave a habitual and start a colony elsewhere
What happens after genetic diversity
Reduction in diversity
What do mutations form
New alleles
What are the stages of natural selection
Individuals with an allele that increases Their chance of survival are more likely reproduce than those without the allele
As such there is a greater frequency of this allele in the next generation of individuals
Over several generations the allele becomes much more common in the population
What are the three categories of adaptations
Behavioural, physiological or anatomical
What are behavioural adaptations
Acts made by an organism that increases its chance of survival
What are of physiological adaptation
Processes that occur inside an organism that increase its chance or survival’s
What is anatomical adaptations
Physical features of an organism that increase its chance of survival
What are the three types of selection
Disruptive
Stabilising
Directional
What is directional selection and what does it cause
When 1 allele is favoured over the other alleles
This causes an increase in the frequency of the allele which gives the organisms a survival advantage
What is stabilising selection
Occurs when alleles towards the middle of the range are favoured
Eg human birth weights
Note 
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