Notatki Danniego part 5 Flashcards
The further the loci, …
the higher the chance of recombinance
-> More chance for a breakage between them
Recombination frequency represents
Recombination frequency equation:
Also: map of the chromosome:
distance between loci:
400 progeny, 44 recombinants
Recombinants/Total
=44/400 = 0.11 = 11%
- Build a map of the chromosome
1% is known as a centimorg
-> distance between loci - Now computers can recognise overlaps in fragments of DNA and stitch it together much quicker
3 point cross
P1 aa bb cc X ++ ++ ++
mutant wild type
f1: +a +b +c heterozygote wild types
Backcross with mutant stock
f2 Expect equal numbers of 8 possible combinations (2^3)
Expected 1:1:1:1:1:1:1:1
mutations Scute - bigger bristles on b ack of drosophila
Echinus - hairy eyes
Crossvainless - missing support structure in wing
P1: scsc ecec cvcv X ++ ++ ++
F1: sc+ ec+ cv+ triple hetorozygotes
F2: Expected equal combinations 1:1….
Actually:
sc ec cv 417 normal 430 sc ++ ++ 25 \++ ec ++ 29 \++ ++ cv 44 sc ec ++ 37 sc ++ cv ? \++ ec cv ?
Parentals ec cv = 417 + 29 \ in total 901
+ + = 430 + 25 /
Recombinants sc + = 25 \ in total 54
+ ec = 29 /
Map distance between scute x echinus = 54/982 = 5.5 map units
PRZEJRZEĆ BO COŚ MI TU NIE PASUJE
3 point cross question
Phenotype frequency:
A. x y z 501
B. + + + 487
C. x y + 15
D. + + z 10
E. x + + 16
F. + y z 9
total 1038
x and y : E + F = 25/1038 = 2,4
y and z : C + D = 25/1038 = 2.4
x and z : C+ D+ E+ F = 50/1038= 4,8
4.8 x y z 2.4 2.4
Rec frequency:
x-y= 0.024
y-z= 0.024
- 024^2= 0.000576
- 000576 x 1038 = 0.60
3 point cross: double crossovers
ZDJECIE TABELKI
- Double crossover unlikely in a short stretch of DNA
cv and c+ : C+ D+ G+ H= 93 93/1448= 6.4
c+ and ve : E+ F+ G+ H= 193 193/1448= 13.2
cv and ve : C+ D+ E+ F= 268 268/1448=18.5
6.4+13.2 =/ 18.5
figures don’t add up because you need to take into account the double crossover
-> G and H must be counted twice when computing map distances
cv and ve : C+ D+ E+ F+ 2(G+H)
45+ 40+ 89+ 94+ 2(3+5) = 284
284/1448= 19.6 map units
cv-c+ (6.4) + c+-ve (13.2)= 19.6
Coefficient of interference
Compares actual number of double crossovers with no. of expected igf each crossover is independent
- > is the number of recombinants over A-B-C equal to the product of A-B x B-C
- > if not there is CHIASMA INTERFERENCE
Recombination frequency cv-c+ = 0.064
Recombination frequency c+-ve = 0.132
Expected proportion of double recombinants =
= 0.064 x 01.132= 0.0084
0.0084 x 1448 = 12 double recombinants
Interference:
Expected 12 double recombinants
Observed only 8
Observed/Expected
8/12 = 0.66
COEFFICIENT OF INTERFERENCE=
= 1 - 0.66 = 0.33
- > females have a higher recombination rate
- > male drosophila never recombine
- > recombination hotspots
Drosophila in adolescence have ….
peculiar chromosomes in spit glands
- > need to make silk protein
- > 100s of copies of the gene
- > Endomytosis - replicate the genes within those cells
- > 1024 bands lined up
FISH -
Fluorescent In Situ Hybridisation
- > Where in genome in sequence for β-chain haemoglobin?
- > Sequence the protein
- > Infer the DNA sequence for protein
- > make mirror image of sequence
- > dye the image
- > finds opposite strand on DNA and binds whilst still dyed
- > Now you know where the gene for β-chain haemoglobin is
Drosophila larva salivary glands have huge chromosome - like structures made up of 1024 individual chromosomes lying close together as a single structure
-> …
-> Polytene chromosomes
These come from ENDOMITOSIS; the multiplying of copies of a gene leaded in large amount; in this case the one used in making the protein pupa
Positron effect variegation
- Gene is shifted by translocation close to the edge of some heterochromatin
- > DROSOPHILA WHITE EYE IS ON X ( potem zmnieszyć, jak już zrobimy diseases list) but can be translocated to chromosome 4
- > is usually recessive
- > normal allele loses part of its dominance after translocation
- > results in white and red patches - Cell division genes translocated to near active parts of DNA
- Causes out of control growth
- Cancer tumours
Somatic Cell Hybridization
Attacking a mouse and human cell together to make a hybrid
- Sendai virus
- > sticks to mouse cell
- > human cell floats past and also sticks to virus
- > virus tries to get in, cells open up = hybrid cell
- > Heterokaryote
Sorting the hybrid cells from normal cells
- use a poison that needs two enzymes (A and B) to break it down
- Mouse line is A- B+ (dies)
- Human line is A+ B- (dies)
Half of the hybrid cells are A+ B+ (survives)
-> half the hybrids are A- B- (dies) - > Human chromosomes are rejected
- > Irradiate hybrid lives and slit into tiny places
- > only small part is ejected
Haplotype
A set of DNA variations or polymorphisms that tend to be inherited together
Selective sweep
- The reduction or elimination of variation among the nucleotides in neighbouring DNA of a mutation as the result of recend and strong positive natural selection
- Example:
- > Drosophila mutation for insecticide resistance in the 40s/50s
- > Now every fly that is tested has a long (thousands of bp) section of DNA that is the same/unbroken
- > Recombination is rarely found in this section
Gene & Environment - linked together
siamese cat - mutant
coat colour due to ability to make melanin.
Siamese has black nose, feet, tail, white body
Mutation is damage to an enzyme that makes it unable to work in hot environments
- > colder parts of the body can make melanin (black pigment) such as ears/nose/tail
- > intersection with temperature
- > temperature sensitive mutation
In drosophila similar effect (temperature sensitive mutation) with eye colour
- > heat shock in 2 hour window 12 hours before turning into flies is critical moment for eye colour
- > this must be when eye coloured gene is switched on
Arctic hare
- > white in winter, grey in summer
- > result of day length
- > also same as autumn leaves (day length)
- > cryptochrome pigment
Nutritical Conditional mutations
- some E coli cannot make their own tryptophane so will not grow on medium unless it contains tryptophane
PKU (phenyloketonuria) metabolism
In a person without PKU:
Phenylalanine—————————————->Tyrosine
Phenylalanine-hydroxylase
In a person with PKU:
Phenylalanine
Phenylalanine ——————————— X
Phenylalanine
No phenylalanine-hydroxylase
Build up of phenylalanine to toxic levels
- > severe mental disorder; lighter hair; fair skin
- > can be worked around with special diet
Werewolfism may be actually porphyria
inability to break down haem pigment of blood
- > Break down red blood cells, get amino acids and pass out haem group in urine
- > In porphyria, porphyrins collect in skin; increased light-sensitivity
- > Blisters form in sunlight
- > Red urine
- > Cannot break down barbiturates
Obesity - gene/environment interaction
-> Morbidly obese BMI >= 30
-> America % of obese 20%, most 25-29% and a few 30% >
-> UK highest obesity rates in Europe ~ 25%
-> Richest are thinner, used to be other way round
-> Increased risk of adult onset diabetes
Food expenditure share of disposable income
1930 -24%
2010 -9.5%
Cheaper sugary foods
Obesity - gene interaction differences
Environment:
- diet, exercise
Genetics:
- hormone leptin
- leptin suppresses hunger
- satiety hormones
- leptin deficiency can make you always feel hungry - keep eating
FTO gene in mice, causes …, but is ….
fused toes
appetite deppressant
human genes for obesity:
TT (1kg less than AT)
AT ( 0 - average)
AA ( 2 kg more than AT)
