Lecture 2

Question 1

what was the blending theory?

Answer 1

traits of parents get mixed like fluid in offspring to make new traits –> the old traits are LOST and cannot be recovered

Question 2

how did Mendel test the blending theory?

conclusion from this experiment

Answer 2

1. crossed purple pea plant with white pea plant –> F1 were purple
2. then selfed the F1s –> would expect only purple F2 if blending theory was correct BUT got some white progeny

Question 3

what were Mendel’s 2 conclusions from his experiment to test the blending theory?

Answer 3

1. presence of white means parental traits are RECOVERED and do not get lost
2. the “element” responsible for the trait acts as a PARTICLE not fluid that can be maintained and separated

Question 4

what is the ratio of phenotype in F2 progeny made from F1 x F1 monohybrid cross?

Answer 4

3:1

dominant:recessive

Question 5

describe Mendel’s model

Answer 5

2 copies of an element are inherited from parents but only 1 is VISIBLE and only 1 is passed to the next generation

Question 6

in a monohybrid cross, describe the probability of each allele being passed down

Answer 6

each allele has an EQUAL PROBABILITY of being passed down

Question 7

if each allele has same probability of being passed down, why is the ratio of dominant to recessive traits 3:1?

think punnett square

Answer 7

since it is a monohybrid cross, 3/4 of the element combinations will have at least 1 dominant trait –> 3 will have dominant phenotype

Question 8

3 reasons why Mendel’s experiments work?

Answer 8

1. the traits he studied are only affected by 1 gene
2. pure genetic background of plants and ability to control cross/mating
3. ability to obtain large number of progeny

Question 9

why is it important to be able to obtain a large number of progeny?

Answer 9

1. low probability events can happen at any time during data collection
2. large sample size helps with precision
3. large sample size reduces variability

Question 10

describe what is produced from meiosis of a cell with A/a alleles

Answer 10

4 gametes –> A, A, a, a

produces SAME RATIO of A and a, so there is an equal chance of transmitting A or a

Question 11

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?

Answer 11

maternal and paternal traits have equal chance of being passed on

Question 12

describe what happens in meiosis

Answer 12

1. 1 A chromosome, 1 a chromosome
2. each chromosome replicates
3. the 2 homologous pairs come together
4. 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
5. these 2 cells each divide so there are 4 cells, 2 with 1 A chromosome each and 2 with 1 a chromosome each

Question 13

can a male sterile plant be fertilized?

Answer 13

yes bc has no anther but does have stigma

Question 14

what is a testcross?

Answer 14

cross an individual with FULLY RECESSIVE individual

Question 15

what is the purpose of a testcross?

Answer 15

to determine the genotype of a testee

Question 16

if you do a testcross and get progeny that are 100% purple, what was the genotype of the testee?

Answer 16

we know something is being crossed with recessive a/a (bc testcross)

so for everything to be purple, testee must be A/A

Question 17

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?

Answer 17

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

Question 18

what is loss of function mutation?

Answer 18

loss of function mutation is a mutation that kills protein function

Question 19

are loss of function mutations usually recessive or dominant? why?

Answer 19

LOF = recessive

the remaining WT copy can mask the loss of function and compensate to give the normal function –> HAPLOSUFFICIENT

Question 20

what are the chances of 2 CF carrier parent having a child with CF? why?

Answer 20

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

Question 21

why is the prevalence of CF in Canada around 1/3600 when 1/30 are carriers?

Answer 21

HAPLOSUFFICIENT –> even if carrier, the WT gene will compensate

only when person is homozygous for the mutation will they have CF phenotype