lecture 2 Flashcards
what is blending theory
hypothesis
traits of parents get mixed like fluid in the offspring = results in new traits that resembles parents
what is the prediction of blending theory
if blended like fluid = parents traits are lost in offspring and cannot be recovered
mendel tested blending theory
describe mendels method
purple petals = take pollen and cross with other - white petal
fertilize stigma - where took of anthers = controls genotype
prevented self pollination
controlled the crosses between different purebred pea plants - control trait from one generation to next - important for farmers
describe plants - mendels method
plants are hermaphrodites = have stigma and anther
can self fertilize but cutting anthers prevents self fertilization
what is mendels first experiment and result
white cross purple = purple 100% F1 = maybe they do not blend
how to test this = see if blending theory works = mendels experiment 2
what is mendels second experiment and result
F1 purple petals = self cross of F1 - monohybrid cross
expectations = should be all purple
result = recovered fraction of white flowers from purple F1 mono cross
what did mendels 2nd experiment prove
argues against blending theory
white flowers = means parental traits do not get lost
suggests element responsible for flower colour (trait/phenotype) works like particles and not fluid - can be maintained from one gen to next and separated
what else did mendel do - after the 2 experiments
many diff experiments with 7 diff traits
F1 = looked like dominant trait, hid recessive
F2 ratio = approx 3:1, certain way traits are mediated
what 2 things did mendels further experiments prove
there is a dominant trait that hides the recessive trait
element producing traits are transmitted to next gen in predictable pattern
when was mendels hypothesis/model
1866
what is mendels model
there are 2 copies of the element that are inherited from parents - diploid organism - only one of the 2 is visible - dominant/recessive
only one of the 2 is transmitted to next gen
describe what happens in monohybrid cross in mendel’s model
each of 2 parental elements have an equal chance of being transmitted to the next generation
3 out of 4 possible element combos in the offspring contain at least one dominant trait = 3:1 ratio of dominant and recessive traits, equal chance of how dom and recessive traits transmit
describe punnet square
all alleles
equal chances - no bias from one trait to other
3:1 ratio - monohybrid cross
name the 3 reasons why mendels experiments worked
traits affected by only one gene - many traits, like height, are affected by multiple genes
pure genetic background and ability to cross or self pollinate = must be able to control cross or mating
ability to obtain a large number of progeny - tested large number of F2s
Why is the ability to obtain a large number of progeny important?
low probability events can happen at any time during the data collection
large sample size helps to determine precise data
large sample size reduces variability between experiments
what is the element
the gene
describe drosophila - element
few chromosomes
weird morphological differences compare to wild type - identified mutants before genes - knew phenotype before identifying gene responsible
traits determined by a single gene
what is the base of mendels law
Meiosis in the GERM CELL is the cellular/molecular base of Mendel’s law
describe what happens during meiosis
a A/a cell produces 4 gamete = 2 x A and 2 x a
meiosis produces the same ratio of A to a, giving an equal chance of transmitting between A or a
maternal and paternal have equal chances of being passed on to offspring
define monohybrid
heterozygote of a gene
describe monohybrid cross
self pollination
only 1 of 4 gametes (from meiosis) is transmitted to the next generation, one egg and one sperm (pollen)
fertilization is a random event, need large number of test products
phenotypically = 3 purple, 1 white
define testcross
the cross of an individual to a
fully recessive individual
what is test cross useful for
determining genotype of a testee = whats being tested
way to see if 2 or 1 copy of dominant element
describe test cross experiment
1 = purple (P/P) + fully recessive (w/w) = 100% purple, heterozygous
#2 = purple (P/w) + fully recessive (w/w) = 50/50 purple and white
phenotypes of progeny depends on genotype of testee
what is loss of function mutation
molecular term
lose function of gene product
mutation kills kinase activity = function of protein
what is recessive
phenotype
what is haplosufficient
even if one functional copy = sufficient to carry out function of gene
describe loss of function mutations
often recessive since a single wild type copy of the gene can often provide necessary functions for the organism
most genes (wild type) are haplosufficient
describe genetic disorders and cousin marriage
in family = cousins could have same mutation and then offspring would have 2 copies of mutated genes
what is cystic fibrosis
view as a mendelian disorder
affects cells that produce mucus, sweat and digestive juices such as the lung, affects tissue and cells that produce mucus
describe prevalence of cystic fibrosis and why
in canada = around 1/3600 and around 1/30 is a carrier
what is cystic fibrosis caused by
mutation in the cystic fibrosis transmembrane receptor = CFTR gene
needed for good functioning
exports chloride
gene identified by researchers at hospital for sick children - toronto
what are chances of having a child with CF
2 carrier parents have 1 in 4 chances of having a child with cf bc cf is a haplosufficient gene
what does allele mean
diff forms of single gene
name and describe the classes of CFTR mutations
normal = exports chloride, 100%
class I, II, III = no pump chloride, complete elimination of protein function, 0%
class IV, V = not as efficient but some function to export chloride, better off than other mutant cases, 10%
describe CF as a haplosufficient gene
missing half = results in cellular defect. loss of function mutation, but dominant
cf develops if homozygous for it
if carry one mutant with one functional copy = sufficient, no cf
cases = loss of function mutation, phenotypically dominant trait
