lecture 7 Flashcards
does all genetics fall under mendelian theory
uhmm nooooooo
describe what protein function does - for gene inheritance
affects how it inherits, ratio and how they inherit changes
does not fit mendels law
what is pleiotropy
the property of a single gene product affecting two or more seemingly unrelated traits
describe mutations in haplosufficient genes
RECESSIVE
most loss of function is recessive
must be homozygous to see mutation
what are dominant mutations
having a single copy of the mutation produces a phenotype - disease - despite having a wild type copy of gene
describe oncogenes
many are activated by dominant mutations
can loss of function mutations be dominant
YEEEE
describe gain of function mutation
activating mutation
dont see it since helps protein gain function
name dominant mutation models
haploinsufficiency and dominant negative
Describe haploinsufficient genes
need 2 full copies of wild type to cause phenotype
describe haploinsufficiency model
2 doses = wild type
0 doses = mutant
1 dose = mutant, since inadequate
describe dominant negative model
protein dimerizes, 2 functional = wild type
2 mutants = mutant
1 mutant and 1 functional = mutant affects wild type, can still dimerize and will interfere with wildtype, since they physically interact
describe mutations in genes coding ribosomal subunits in drosophila
often dominant, haploinsufficient
Mutation on single copy of gene makes ribosomes = morphological defects = tend to be shorter and thicker
loss of function mutation
cells need full load ribosomes to do what they need to do
describe p53 mutant allels in cancer
function as dominant negative
mutation in the dna binding domain in one of 2 alleles = even if mutated still makes tetramer but wont bind dna, no activation of canonical p54 target genes
what is p53
transcription factor that binds dna as a homotetramer - tetramerizes = 4 proteins come together
describe incomplete or partial dominance (dose determinant)
flower colour = mutation of gene that produces pigments = both copies of enzyme needed for red pure breed
if one functional copy = not sufficient amounts of red so will be pink
red not completely dominant = looks like blending theory kinda
what is codominance
both alleles expressed or detected
describe how blood type determined
2 alles = A, B, i
gene responsible for blood type encodes a glycosyltransferase = puts sugar molecule on another chain
describe what each blood allele does
i = no sugars added
A = will be acetyl galactosamine at end of sugar chain - present on surface of rbc
B = puts simple galactose
describe how codominance is discovered in blood types
AB = will have both sugars
uses antibody that recognizes specific structure
depends on assay
describe A vs B vs O - codominance
A and B are dominant over O
but A and B are codominant with each other in conventional assay
coagulates = see clear phenotype of both = why they are co dominant, both expressed
could also be incomplete dominance if have sensitive assay = quantify number of sugar molecules = end up with number between A and B
how we classify codominance is determined by what
Determined by phenotype we characterize - methods of detection or observation
what is Hb gene
encodes beta globin = subunit of hemoglobin
describe phenotype anemia example
if HbA/HbA = no anemia
if HbS/HbS = anemia
if HbA/HbS = no anemia
as long as one not affected = fine
so sickle cell= recessive
HbA = dominant to HbS
describe phenotype blood cell shape example
if HbA/HbA = normal shape
if HbS/HbS = sickle cell shape
if HbA/HbS = slight sickle cell shape
HbS = incomplete dominance to HbA
aa sequence affected so protein oligomerizes = polymerizes = back = causes shape
describe protein level analysis of blood
could consider sickle cell as codominant = if only looking at presence protein
phenotype = presence of HbA and HbS at protein level
proteins migrate at diff rates = see both phenotypes separately (HbA and HbS = codominant bc both alleles can be clearly discerned at protein level)
if has band in middle =would be incomplete dominance
depends on assay and phenotype
describe recessive lethal
if 2 copies = cannot have organism = will die
often heterozygous for recessive lethal appear normal - since most genes are haplosufficient
can humans carry recessive lethal mutations
yesss
we heterozygous thooo
we healthy since have one healthy copy
describe recessive lethal mutations in diploids vs haploids
in diploids = recessive lethal mutations maintained as heterozygous
in haploids = not possible since only one copy of gene
describe homozygous mutations causing lethality in animals - mice
either recessive or dominant mutations
normal mice = dark, yellow mice = lighter coats
yellow x normal = 1:1, since yellow dom, but 2 copies of dom allele = lethal so we never get it
yellow x yellow = 2:1 (yellow to normal), never get YY = since lethal
gene is dominant when it comes to pigmentation phenotype but recessive for viability bc animal with 2 copies of dom will die
describe conditional alleles
alleles depend on condition = expression of certain features or traits depends on external factors
describe conditional alleles - temp sensitive mutations
at lower temps = gene functions like wild type
at higher temps = gene is nonfunctional and lethal
Depends on conditions
describe conditional alleles - auxotrophs
if on minimal media and arginine = functions like wild type
if on minimal media only = non functional - lethal
what are auxotrophs
organisms that lost the ability to synthesize certain substances required for their growth
describe conditional alleles temp controlled phenotypes - rabbits
black pigmentation at extremities = depends on temp, must lower
tyrosine kinase = active at a lower temp = important for producing pigmentation
wont show colour in middle of rabbit since can control body temp, at extremities = harder to control
what is variable penetrance
percentage of individuals with a given allele who exhibit the phenotype of that allele
can be obvious in one person but not other since factors can contribute
give ex of variable penetrance
BRCA2 mutations predispose to breast, ovarian and pancreatic cancers
why = environment, interacting genes, subtlety of mutant phenotype - difficult to diagnose (psychiatric disorder) = other factors contribute
describe incomplete penetrance and pedigrees
dom mutation
gen 2 = carriers but exception to mendelian rule
not penetrant so not shown but carrier, phenotype not detected or manifested in generation
gen 3 = recovers it
describe variable expressivity
degree to which a given allele is expresses at the phenotypic level = the intensity of the phenotype
describe ex of variance penetrance and expressivity
neurofibromatosis type 1 = single gene mutation
all affected in diff ways
(diff levels of phenotype, expressivity and penetrance) = same factor affecting penetrance may be affecting expressivity among diff individuals
based on assay
what could sick cell be also classified as
snp = yes since caused by single nt chain and prevalent in certain ethnic background
