Genetics Flashcards
Allele
Two genes that occupy the same position on homologous chromosomes and cover the same trait.
Deleterious, mutation or allele
A mutation that causes injury or harm
Types of chromosomal mutation
- Large deletions due to unequal crossing over
- duplication
- inversion
- translocation
Frameshift mutation
A chromosome that comes from the deletion or insertion of a base into a DNA sequence. Results in the shifting of all the following bases after this mutation
Genetic Drift
A process which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
Population
A group of individuals of the same species that live in the same area and can produce fertile offspring
Gene pool
All copies of every type of allele at all loci in every individual in a population
Locus
A specific place along the length of a chromosome where a given gene is located
Assumptions of Hardy-Weinberg law (7)
- Mutation isn’t occurring
- Natural selection isn’t occurring
- The population isn’t infinitely large
- All members of the population breed
- All mating is totally random
- Everyone produces the same number of offspring
- There is no emigration or immigration
Hardy-Weinberg equation
p + q = 1
p2 + 2pq + q2 = 1
Independent assortment
The lining up of chromosomes along the center of the cell in meiosis. This is one of the causes of genetic variation
Microsatellite
This is a short, repeated sequence of DNA that appears at a certain locus on a chromosome
Missense mutation
Change of one base in the DNA sequence resulting in a different amino acid that the codon codes for
Nonsense mutation
Results in a premature stopping of a DNA sequence as a result of a mutation
Nonsynonymous mutation
Nucleotide mutation that alters the amino acid sequence of a protein
Orthogenesis
Also called straight-line evolution, theory that organisms have the tendency to to evolve in a definite direction.
Particulate inheritance
The theory that traits are inherited as discrete units known as genes
PCR
(Polymerase Chain Reaction) A technique for amplifying DNA ‘in vitro’ using specific primers, DNA polymerase and nucleotides
Phenotype
The observable physical and physiological traits or an organism
Genotype
The genetic makeup, or set of alleles of an organism
Pleiotropy
When one gene influences two or more unrelated phenotypic traits. e.g. sickle cell anemia or a gene that affects growth rate will affect height and weight
Polygenic trait
When one characteristic is controlled by two or more genes.
e.g. eye colour
Polyploidy
When cells and organisms contain more than two paired set of chromosomes. (Triploid and Tetraploid etc)
Quantitative trait
Measurable phenotype that depends on many genes and the environment. Examples include height, weight and blood pressure
Isozyme
An enzyme that differs in its amino acid sequence but catalyses the sam reaction
Restriction fragment lenght polymorphism (RFLP)
is a difference in homologous DNA sequences that can be detected by the presence of fragments of different lengths after digestion of the DNA samples
Recombination
pieces of DNA are broken and recombined to produce new combinations of alleles
Segregation of alleles
Alleles become separated and each one enters a single gamete
Selection, balancing
Two alleles are maintained in a population because of natural selection. e.g heterozygote advantage- an individual with Aa has higher fitness than both AA and aa individuals
Natural selection
A process in which certain individuals with certain traits tend to survive and reproduce at higher rates than those without those traits
Selection, disruptive
The extreme traits are favored as opposed to the intermediate ones (M shaped curve)
Selection, directional
An extreme phenotype is favoured over the others causing the allele frequency over time to shift in the direction of that phenotype
Selection, stabilizing
The population stabilizies on a more mean trait value, more bell shaped curve
Silent mutation
Base substitution that results in no change of the amino acid that is coded for due to DNA being degenerate
Simple tandem repeat
A short tandem repeat is a microsatellite, consisting of a unit of two to thirteen nucleotides repeated hundreds of times in a row on the DNA strand.
Single nucleotide polymorphism
A variation of a single nucleotide that occurs at a specific locus on the genome in a population
Synonymous mutation
Change in the codon for an amino acid but not resulting in a change of the amino acid
Threshold traits
Show discrete phenotypes but are controlled by many different loci
Twin studies
Twin studies allow researchers to examine the overall role of genes in the development of a trait or disorder. Can use both identical and non identical twins
What does diversity mean?
Variety of living species (organisms) in an ecosystem
Species
A group of organisms that are capable of producing fertile offspring
Sexual Dimorphism
where the male and female look different from one another
Transformation
a change in genotype and phenotype due to assimilation of foreign DNA
Euchromatin
DNA that is partially or fully uncoiled (loosely packed), is active in gene expression an stains lightly
Chromatin
complex of DNA and protein, and is found in the nucleus of eukaryotic cells
Histones
Proteins that are responsible for the first level of DNA packing in chromatin
What fibers is chromatin organised into?
- 10-nm fiber
- 30-nm fiber
- 300-nm fiber
- metaphase chromosome
Heterochromatin
dense packing, regions of chromatin are highly condensed, difficult for cell to express genetic info
Genome
The complete genetic information contained in an individual - gene+ chromosome
How many different stages of transcription are there?
3 - Initiation, elongation and termination
What happens in the first stage of transcription (Initiation)
- Proteins signal the initiation of RNA synthesis and transcription factors control the binding of RNA polymerase, where it attaches to promoter region on DNA
- TATA box- considered to be the core promoter sequence in eukaryotes, the binding site of general transcription factors or histones
o Core DNA sequence 5’-TATAAA-3’ or some form similar which is usually followed by three or more adenine bases
o The sequence of AT bases means that this TATA box makes it easier for the DNA to unwind as AT bases only form two hydrogen bonds compared to GC which makes three
What happens in the second stage of transcription (Elongation)
Building of mRNA from the 3’ end of the nucleotide polymer with the use of free nucleotides that are available in the nucleus of the cell
- As RNA polymerase moves along the DNA, it untwists the double helix, 10 to 20 bases at a time (40 nucleotides per second in eukaryotes)
- A gene can be transcribed by many RNA polymerases at the same time
What happens in the final stage of transcription (Termination)
- Release of RNA polymerase and mRNA following transcription of the terminator region of the DNA. This is triggered by a release factor.
- The resulting stretch of DNA that is transcribed is called a transcription unit
The termination of transcription is different in bacteria and eukaryotes
Eukaryotes – The polymerase continues transcription after the pre-mRNA is cleaved from the growing RNA chain; the polymerase eventually falls off the DNA
Bacteria - The polymerase stops transcription at the end of the terminator
The central dogma
The concept that cells are governed by a cellular chain of command : DNA-> RNA -> Protein
Translation
The initiation stage of translation brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
• First, a small ribosomal subunit binds with mRNA and a special initiator tRNA • Then the small subunit moves along the mRNA until it reaches the start codon (AUG)
• Proteins called initiation factors bring in the large subunit that completes the translation initiation complex
- Termination occurs when a stop codon in the mRNA reaches the A site of the ribosome
- The A site will then accept a protein called a release factor
- The release factor causes an addition of a water molecule instead of an amino acid
- This reaction releases the polypeptide, and the translation assembly comes apart
Homozygous
Having identical genes for a particular characteristic (AA/aa)
Heterozygous
Having two different genes for a particular characteristic (Aa)
Phenotype
The physical appearance of an organism (genotype and env)
Genotype
The genetic makeup of an organism
Mendel’s three laws
1) Law of dominance
2) Law of segregation
3) Law of independent assortment (two different genes at two different loci
Organic extraction of DNA
Lyse cells with SDS/PK/(DTT)
• Sodium dodecyle sulfate (SDS) – ionic
detergent breaks down cell membranes
(inhibits enzyme activity)
• Proteinase K – degrades proteins at 55C but
not susceptible to SDS. Dissolves histones
• Dithiothreitol (DTT) – additive for difficult lysis
conditions, breaks disulfide bonds in strong
proteins like keratin
The three steps of PCR
Denaturation, Annealing, Extension
First step of PCR
Denaturation
DNA heated to 94C which breaks hydrogen bonds
Second step of PCR
Primer annealing (55C)
- Oligonucleotides serve as primers for the DNA polymerase
- Target a specific sequence of base pairs
- Require a primer for each end of the two strands that will defin the ends of the molecule synthesised
Third step of PCR
Extension (72C)
- DNA polymerase extends the primers, adding nucleotides onto the primer in a sequential manner
- Commonly use Taq polymerase as heat tolerant
Gel electrophoresis
- Separates fragments according to size
- Molecules pushed by an electrical field through a gel that contains small pores
Restriction enzymes
Recognize specific nucleotide sequences and then cut both strands of the DNA molecules. Often recognize palindromic sequences.
Used in DNA cloning, DNA fingerprinting and to quantify genetic variation
Polymorphic
the presence of more than one allele at a locus
Heterozygosity
Measure of genetic variation that accounts for either the observed or expected proportion of individuals in a population that are heterozygotes
Allozymes
different allelic forms of a protein
Isozymes
different proteins that do the same job, but are produced from different loci
Restriction site fragment length poylymorphism
RFLP for short
- Amplify a region by PCR
- Then cut (digest) with a restriction endonuclease
Microsatellites
Tandem repeats of short sequence of base pairs:
cgtcgtcgtcgtcgt
number of repeats at polymorphic locus ranges from 5-100
Used in forensics/population genetics/conservation
Hardy-Weinberg Law
p2 + 2pq + q2 = 1 After one generation of random mating the genotype and allele frequencies will remain at these frequencies in perpetuity in the absence of other forces
Some of the effects of genetic drift
- changes allele frequencies
- erodes genetic variation in populations
- is a process that particularly affects small populations
Discrete Variability
Polymorphisms which can be scored by simple visual methods. Presence /absence of certain characteristics
Meristic characters
values of these characters are restricted to integers therefore they are countable. e.g. number of vertebrae, fingerprint ridges, clutch size
Threshold characters
Characters with discrete alternatives. Expression of alternatives is determined by a threshold in an underlying continuously distributed trait being exceeded.
- adult-onset diabetes
- heart disease
Quantitative traits are influenced by
Environmental factors and many genes
Threshold traits
Coronary heart disease is not a continuous trait
but it is associated with many factors
- weight, diet, cholesterol, smoking, family history
add up to liability
Above a threshold value will be liable to the
trait
Standard deviation
The spread of results about the mean
Heritability
The proportion of a populations phenotypic variation attributable to the genetic factors
Broad-sense heritability
the contribution of genetic factors to the total phenotypic variance
Narrow-sense heritability
the contribution of additive genetic factors alone to the total phenotypic variance
Infanticide
The killing of young offspring by an older organism of the same species
