Lecture 2 Flashcards
what was the blending theory?
traits of parents get mixed like fluid in offspring to make new traits –> the old traits are LOST and cannot be recovered
how did Mendel test the blending theory?
conclusion from this experiment
- crossed purple pea plant with white pea plant –> F1 were purple
- then selfed the F1s –> would expect only purple F2 if blending theory was correct BUT got some white progeny
what were Mendel’s 2 conclusions from his experiment to test the blending theory?
- presence of white means parental traits are RECOVERED and do not get lost
- the “element” responsible for the trait acts as a PARTICLE not fluid that can be maintained and separated
what is the ratio of phenotype in F2 progeny made from F1 x F1 monohybrid cross?
3:1
dominant:recessive
describe Mendel’s model
2 copies of an element are inherited from parents but only 1 is VISIBLE and only 1 is passed to the next generation
in a monohybrid cross, describe the probability of each allele being passed down
each allele has an EQUAL PROBABILITY of being passed down
if each allele has same probability of being passed down, why is the ratio of dominant to recessive traits 3:1?
think punnett square
since it is a monohybrid cross, 3/4 of the element combinations will have at least 1 dominant trait –> 3 will have dominant phenotype
3 reasons why Mendel’s experiments work?
- the traits he studied are only affected by 1 gene
- pure genetic background of plants and ability to control cross/mating
- ability to obtain large number of progeny
why is it important to be able to obtain a large number of progeny?
- low probability events can happen at any time during data collection
- large sample size helps with precision
- large sample size reduces variability
describe what is produced from meiosis of a cell with A/a alleles
4 gametes –> A, A, a, a
produces SAME RATIO of A and a, so there is an equal chance of transmitting A or a
if there is equal chance of transmitting A or a from A/a cell, how can we put this in terms of maternal and paternal traits?
maternal and paternal traits have equal chance of being passed on
describe what happens in meiosis
- 1 A chromosome, 1 a chromosome
- each chromosome replicates
- the 2 homologous pairs come together
- the 2 homologous pairs separate and the cell divides so there are 2 cells, 1 with 2 A chromosomes, the other with 2 a chromosomes
- these 2 cells each divide so there are 4 cells, 2 with 1 A chromosome each and 2 with 1 a chromosome each
can a male sterile plant be fertilized?
yes bc has no anther but does have stigma
what is a testcross?
cross an individual with FULLY RECESSIVE individual
what is the purpose of a testcross?
to determine the genotype of a testee
if you do a testcross and get progeny that are 100% purple, what was the genotype of the testee?
we know something is being crossed with recessive a/a (bc testcross)
so for everything to be purple, testee must be A/A
if you do a testcross and get 50% progeny that are purple and 50% progeny that are white, what was the genotype of the testee?
we know something is being crossed with recessive a/a (bc testcross)
so to get some white and some purple, testee must be A/a
what is loss of function mutation?
loss of function mutation is a mutation that kills protein function
are loss of function mutations usually recessive or dominant? why?
LOF = recessive
the remaining WT copy can mask the loss of function and compensate to give the normal function –> HAPLOSUFFICIENT
what are the chances of 2 CF carrier parent having a child with CF? why?
if both parents are carriers, they have 1/4 chances of having a child with CF bc CFTR is HAPLOSUFFICIENT –> i.e. LOF mutation is recessive
why is the prevalence of CF in Canada around 1/3600 when 1/30 are carriers?
HAPLOSUFFICIENT –> even if carrier, the WT gene will compensate
only when person is homozygous for the mutation will they have CF phenotype
