L11-14: Eukaryotic genes and transcripts & Inheritance Flashcards
What does polycistronic mean?
It is when clustered genes are often transcribed as a single molecule or mRNA
What parts of the transcription unit are not encoded in the genome?
The cap and the poly A tail
How do differences in gene organisation impact geneticsin eukaryotes and prokaryotes?
In prokaryotes if there is a mutation it effects the recognition of all genes but in eukaryotes its only impacts one
What are transcription promotors?
Region of DNA upstream that contains specific nucleotide sequences that transcription factors associate with which allows the recruitment of RNA polymerase
What are the key features of prokaryotic promotors?
Conserved sequences upstream
Conserved sequences recognised by sigma factor which positions the polymerase:
RNA pol + sigma factor = holoenzyme
What are the RNA polymerases in eukaryotes?
RNA pol I - rRNA
RNA pol II - all protein coding genes
RNA pol III - tRNA, 5S rRNA and other small ‘non-coding RNAs’
What are features of RNA polymerase II in eukaryotes?
TATA-box that is bound by the transcription factor IID complex
TFIID recruits other TFs and RNA polymerase II
5’ cap is added while mRNA is transcribed
When is the poly A tail added?
At a specific signal AAUAA when RNA is cut releasing it from the DNA then the poly A tail is added
What is a microarray?
DNA corresponding to each gene in the organisms genome spotted onto a slide
How does splicing take place?
Spliceosome removes introns from RNA
What are the functions of the small and large subunits of the ribosome?
Small: reading mRNA, finding ORF and interpreting the codon
Large: synthetic peptidyl transferase centre
How does bacterial translation take place?
Using the Shine-Dalgarno sequence which is recognised by the small subunit by base pairing
Large and small subunit bind which initiates translation
How is translation initiated in eukaryotes?
Small subunit binds to cap and moves along to the first AUG
How are genes polygenic?
When multiple genes interact
What is the difference between linked and unlinked genes?
Linked genes cannot assort independently whereas unlinked can
What phenotypic and genotypic ratios are typically used to work out allele frequency?
1:2:1 and 3:1
What is the Hardy-Weinburg equation?
p^2+2pq+q^2=(p+q)^2=1
How do populations retain genetic variability?
Due to the genotypic ratios in a randomly-breeding population remaining constant from generation to generation
When does Hardy-Weinburg not apply?
Gene flow
Genetic drift
Nonrandom mating
Natural selection
What does Hardy-Weinburg assume?
Large population, random mating and no evolutionary forces acting
What are examples of human autosomal recessive conditions?
Albinism
Phenylketoneuria
Tay-Sachs
CF
Sickle-cell anemia
Haemochromatosis
What are examples of autosomal dominant conditions?
Huntington’s
Polycystic kidney disease
Achondroplastic dwarfism
Polydactyly
Hypercholesterolemia
FASPS
What are characteristics of sex linkage?
X and Y share little homology
X has more genes than Y
Many genes on Y are for male sex determination
Many genes on X that are not involved in determination
The presence of a gene on X or Y leads to distinct patterns of inheritance
What are examples of X-linked recessive disorders in humans?
Haemophilia
Duchenne & Becker muscular dystrophies
Fragile-X syndrome
Deuteranopia (colourblindness)
What is haemophilia?
Failure of the blood to clot which is caused by the absence of Factor VIII (ran in royal family)
What is an example of a Y-linked disorder?
Retinitis pigmentosa
What is Leri-Weill dyschondrosteosis?
Disorder of bone growth, caused by mutation/lack of one copy of SHOX gene, SHOX is found on X and Y
What terms are used in the relationship of genotype to phenotype?
Penetrance & expressivity
Pleiotrophy
Epistasis
Environmental effects
Complementation
What types of dominance relationships?
Complete, Incomplete and Codominant
What is codominance?
Both alleles are expressed in the phenotype so traits show equally in F1
What is pleiotrophy?
Some genes/alleles of them affect more than one unrelated characteristic, like in manx cats has recessive lethal phenotype
What is epistasis?
Where one mutation hides/modifies the phenotype of another gene that is epistatic to another modifies/masks its phenotype
What does hypostatic mean?
The gene whose phenotype is modified/masked in epistasis
What is penetrance?
It describes how many members of a population with a particular genotype show the expected phenotype
What is variable expressivity?
The range of signs and symptoms that can occur in different people with the same genetic condition
What is an example of incomplete penetrance and variable expressivity?
Polydactyly
How do environmental effects impact phenotype?
Temperature is one element
e.g. Siamese cats for a thermosensitive allele which encodes an enzyme catalysing melanin production
What is a complementation group?
A set of mutations mapping to the same chromosomal locus that fail to complement each other when crossed
What is a key feature of complementation analysis?
Can only be done with recessive alleles
What is intragenic complementation?
A protein has multiple functions or which forms multimers
How are non-parental genotypes formed?
Independent assortment of genes on different chromosomes
Breakage and rejoining of homologous chromosomes during meiosis
What is recombination frequency?
RF= (No. of recombinants/ total progeny) x100
What is the centimorgan?
It is a map unit, 2 loci are one centimorgan apart if recombination is observed between them in 1% of meiosises
How are genetic and physical maps used?
Not co-linear
Recombination is not random along chromosomes ‘hot spots’
More of an approximation to the physical map from genetic data
