The rest of module 2 Flashcards
What is a gene
A defined region (sequence) of DNA that produces a type of RNA molecule that has some function
Gene expression definition
The process by which information from a gene is used in the synthesis of a functional gene product
How does RNA polymerase synthesise mRNA
Catalyses formation of phosphodiester bonds between ribonucleotides
What are the three stages of transcription
Initiation, elongation, termination
What occurs in the initiation stage of transcription
Transcription factors bind to promoter region (TATA box), RNA polymerase II binds forming a transcriptional initiation complex together with transcription factors. 2 DNA strands separate and RNA pol II starts synthesis without the need of a primer
What occurs in the elongation stage of transcription
RNA polymerase II uses the template strand which runs in the 3’->5’ direction as a template and inserts complementary RNA nucleotides in the 5’ -> 3’ direction
What parts of the gene are transcribed
5’ UTR, coding sequence, 3’ UTR
What parts of the gene are translated
Exons
What is splicing
Removal of introns from mRNA strand to make continuous coding sequence
What is pre mRNA
mRNA stored while still containing introns, so that proteins can be made quickly when required
Purpose of promoter region
DNA segment recognised by RNA polymerase to initiate transcription
5’UTR purpose
Contain regulatory elements, facilitates addition of 5’ G cap
3’UTR purpose
Contain regulatory elements, facilitates addition of poly-A tail
5’G cap
Prevents mRNA degradation, promotes intron excision and provides a binding site for the small ribosomal subunit
Poly-A tail
Prevents mRNA degradation, promotes intron excision and facilitates export of mRNA from the nucleus to the cytoplasm
Where does transcription occur in eukaryotes
In the nucleus
Where does translation occur
In the endoplasmic reticulum or cytoplasm
Where does transcription occur in prokaryotes
In the cytoplasm
What is a functional gene product
Protein or non-coding RNA (doesn’t give rise to a protein but has some other function, e.g tRNA, rRNA)
What is a monohybrid cross
Crossing two heterozygotes for one gene
What is the expected phenotype ratio of a monohybrid cross
3:1
What is a test cross
Crossing an unknown genotype but dominant phenotype with a known genotype, recessive phenotype
What are Mendel’s two laws
Law of segregation, law of independent assortment
What is a dihybrid cross
Crossing two heterozygotes for two genes
What is the expected phenotype ratio of a dihybrid cross
9:3:3:1
Product rule
Multiply independent events (e.g unlinked genes)
Sum rule
Add mutually exclusive events
What is a polymorphic trait
A monogenic trait but with many alleles
What is incomplete dominance
When a heterozygote has a blend of the two phenotypes
What is co dominance
When a heterozygote expresses both traits
What is a polygenic trait
A phenotype controlled by the additive effects of many genes (groups of genes). Characters appear continuous or quantitative (non discrete)
What are examples of apparent exceptions to Mendel’s laws
Co dominance, incomplete dominance, polymorphism
How does the environment affect phenotype
Smooths differences between phenotypes (continuous traits can have a simple genetic basis)
Polygenic vs polymorphic
Polygenic: trait which has many genes causing it
Polymorphic: gene which has many alleles
What is a sex linked trait
Involving genes on sex chromosomes
Around how many linked genes are there per chromosome
1000
What is the recombinant frequency
The proportion of recombinant gametes
How do you calculate the recombinant frequency
Recombinant phenotypes/ total phenotypes
What is the approximate recombinant frequency for distant (unlinked) genes
~50%
What is the recombinant frequency for linked genes
0-50%
What type of relationship is there between distance between linked genes and recombination frequency
Linear
What is the centimorgan
Arbitrary unit used for measuring distance between linked genes. cM = 100 x recombination frequency
What is a map unit and how long is a chromosome
Same as a centimorgan, a chromosome is about 50 map units
Population definition
Localised group of individuals of the same species
Gene pool definition
Total aggregate of genes (and their alleles) in the population at one time
Hardy-Weinberg Equation
p^2 + 2pq + q^2
Allele frequency Hardy-Weinberg Equation
p+q = 1
What is p Hardy-Weinberg Equation
Frequency of dominant allele
What is q Hardy-Weinberg Equation
Frequency of recessive allele
How can allele frequencies change
Non- random mating (assortative mating, in breeding), random genetic drift, bottleneck effect, founder effect, natural selection, gene flow, migration, mutation
Random genetic drift
A random change in allele frequencies due to sampling error over generations
Bottleneck effect
Catastrophic event results in the death of a random part of the population. Consequential population may not be representative of original
Founder effect
Random event results in the relocation of part of population. Resulting populations may not be representative of original
Stabilising selection
Reduces variation but does not change the mean
Directional selection
Changes the mean value toward one extreme
Disruptive selection
Favours the two extremes producing two peaks
Frequency dependent selection
Natural selection maintains an equal proportion of phenotypes (e.g left and right mouthed perissodus microlepis)
Cline
The gradual geographic change in genetic/phenotypic composition
Migration features
Brings new alleles, changes proportions of existing alleles, changes population size, makes two populations more similar
Centimorgan = (in terms of recombinant frequency)
Centimorgan = 100x recombinant frequency
What are the human examples of sex linked traits
red-green colour blindness (recessive), haemophilia
