Lecture 9 and 10 Flashcards
What is linkage and mapping?
The process of finding out how genes are structured in the genome
Who conducted a dihybrid cross and got some rando results?
Sunders and Bateson
What were the expected dihybrid cross results vs observed?
9:3:3:1
11:1:1:3
(Over representation of parental phenotypes)
What were Sunders and Bateson crossing?
Sweet pea flower colour and pollen shape
What species did Thomas Hunt Morgan work with?
Drosophilia Melanogaster
What did Morgan investigate?
Traits that followed a sex linked pattern of inheritance (body colour, eye colour, wing length)
What did the F1 generation of Drosophilia Melanogaster contain?
Wild type females
Yellow bodied, white eyed, minature winged males
What was Morgan’s explanation for a higher proportion of the F2 generation having parental combinations?
All three genes located together, transmitted together
What is recombination frequency?
Proportion of offspring not of either parents phenotype
How can we tell Morgan’s results weren’t a fluke?
Chi squared test
What is the chi squared test formula?
x^2=TOTAL (number observed-number expected)^2/number expected
When is a p value significant?
less than 0.001?
Who and when were the first genetic map constructed?
Alfred Sturtevant, 1911
1% recombination frequency=
1cM = 1 map unit
How to find RF using crossing?
Add up all individuals recombinant for two pairs of gene and divide by total individuals
Who visualised recombination using microscope?
McClintock and Creighton (Maize) Curt Stern (Drosophilia)
Why is maize a good model?
Each cob has hundreds of kernel, an outcome from a cross
Maize had what abnormal chromosome, visible under a microscope and use as a genetic marker?
Chromosome 9
No known phenotypic effect
What are the kernel colour genotypes for maize?
C coloured
c colourless
What are the kernal endosperm texture genotypes for maize?
Wx starchy endosperm
wx waxy endosperm
What were McClintock and creighton’s conclusions?
Cross over occured between C and wx gene, genetic recombination involves physical exhcnage of segments
What do double recombinants do?
Shrink map distance if not counted
Why are the number of double recombinants lower then expected?
Interference
What is interference?
Crossing over becomes physically impossible with decreased distance between loci
What is the maxium distance on genetic maps and why?
50 RF (cM) because double cross over occurs
What name is given to places where the recombination rate is higher then expected?
Recombinant hotspots
Recombination and interference are _____ events.
Controlled
How does recombination differ in human males and females?
Recombination rate twice in males then females
What are the two types of point mutation?
Forward mutation (away from ancestral sequence) Reverse mutation (back to ancestral sequence)
Who first showed that x-rays generate mutation of drosophilia?
Thomas Hunt Morgan
What diseases often have a neurological phenotype?
Trinucleotide repeat diseases
What do trinucleotide repeat diseases show?
Anticipation (disease onset gets younger down the generation)
What enzyme works during photo repair and what does it do?
Photolyase recognises thymine dimers and reverses
Why is this mechanism called photo repair?
Only works in the presence of light
How is guanine removed?
Alkyltransferase
What proteins scan DNA for distortion in nucleotide excision repair?
UvrA and UvrB
What happens when distortion is found in nucleotide excision repair?
UvrC combines with UvrB and nick the DNA at 7 and 4bp
What happens after the DNA has been nicked during nucleotide excision repair?
DNA polymerase fills the gap, ligase joins new to old
What enzyme recognises and removes bases during base excision?
Glycosylase
What site is left behind after glycosylase removes a base?
Apurinic or apyrimidinic site
What enzyme recognises and makes a single strand break during base excision?
AP endonuclease
What happens after AP endonuclease is done?
Exonuclease removes a few bases which is then backfilled with polymerase and ligase
What type of repair occurs when double strand breaks happen?
Nonhomologous end joining
What type of repair correct polymerase errors by copying existing strand?
Methyl-directed repair
How does methyl-directed repair detect original strand?
Methyl group (only in bacteria) Errors identified and replaced using base excision repair
What is an auxotroph?
A strain that needs a specific supplement
What is a prototroph?
An organism that can grown on minimal media
What bread mould was experimented on?
Neurospora crassa
What did Beadle and tatum propose by testing each supplement?
One gene=one enzyme
What is black urine disease known as?
Alkaptonuria
Who studied Alkaptonuria in families?
Archibald Garrod
What did Garrod find?
Homogentisic acid accumulates in the urine, enzyme that breaks this down is absent in the patients
What enzyme is mutated in phenylketonuria?
Phenylalanline hydroxylase
Retina cells have ______ transmembrane proteins.
7
Each retina cell evolved from the orginal ____ gene.
Rhodopsin
How many light sensitive proteins are there in rod and cone cells?
4
How many single variants in the rhodopsin gene lead to progressive sight loss? reduce sensisitivty to light?
29
2
What variant in the red receptor causes red colour blindness?
Cys203>Arg variant
