CBG14

Question 1

1. A———B 2. A———b a———-b a———B

Answer 1

1. cis coupling 2. trans repulsion

Question 2

What increases the probability of gene recombination?

Answer 2

increases the further apart the gene llocu are - greater interlocus distance

Question 3

What are the units of genetic maps produced from RF?

Answer 3

cM - centimorgans or mu 1 mu = distance between genes that produce 1% recombinant offspring 1mu=1% RF

Question 4

What does recombination frequency not depend on?

Answer 4

gene configuration RF is the same whether the genes in double/hetero, dihybrid cis or trans

Question 5

How can linkage be detected?

Answer 5

a two point test cross and recombination between 2 genes calculated

Question 6

What % RF is there at linked syntenic loci?

Answer 6

0-50% recombination occurs by reciprocal crossing over in pachytene

Question 7

What %RF does non syntenic loci show?

Answer 7

50% RF -recombination occurs by independent assortment

Question 8

What %RF is there at un linked syntenic loci?

Answer 8

50% RF - so far apart that crossing over causes genes to assort independently.

Question 9

if RF=50% what type of connection do the genes have?

Answer 9

cannot tell if syntenic or non syntenic from a single cross

Question 10

How do you calculate whether syntenic and linked?

Answer 10

eg. B on x chromosome want to map locus relative to y initial cross = 50% RF Y x B need more crosses from the same chromosome as y or b ie. linkage group to check whether syntenic or linked eg. y x sn 21%RF sn x B = 36% RF yxB =57 cM =syntenic but unliked 57% RF cant be realised in a y x B cross

Question 11

Why would a single cross over only result in 50% recombinance?

Answer 11

as only 2/4 of non sister chromatids are involved. A—-B A—-B

Question 12

What is needed in total to map relative position of 3 genes?

Answer 12

3 cross overs eg. trihybrid cross. test cross DdEeFf x ddeeff 1000F2 3 traits of interest most frequent types of gametes will be the parental types with no recombinant crossover occuring recombinants results from single or double cross over.

Question 13

How do you calculate relative position of genes compared to each other after test crosses?

Answer 13

1. identify parent and recombinant types. 2. work out %RF for pairs of loci, eg. D/E D/F E/F using eqn. 3. if all are smaller than 50% then linked and syntenic 4. can sue number to work out relative gene order. D/E = 22.5 D/F=18 E/F =5.5 D—-F–E 5. investigate recombinant categories DCO is rarer eg. DFE and dfe 6. work out origin of all recombinant genotypes - lowest likely to be DCO 7. correct gene distance to include DCO. eg. calculate RF with DCO as x2

Question 14

What is interferance?

Answer 14

crossovers in chromosome regions affects liklihood of crossover in adjacent region

Question 15

What is the coefficient of coincidence?

Answer 15

observed number or frequency of DCO divided by expected number of frequency of DCo interferance = 1-COC - no DCO = complete interferance =1 1-0 =1 no intereance ob=exp =1 1-1=0

Question 16

How do you calculate number of expected DCO?

Answer 16

probability of 2 single crossovers occuring independently = RF interval/100 x RF interval2/100 x number of offspring = expected.

Question 17

What is mapping accuracy effected by?

Answer 17

chromosome interferance reducing no. of DCO and undetected recombinant.

Question 18

What do mapping functions describe?

Answer 18

relationship between map units and %RF and corrects for effect of multiple crossover and interferance interferance doesnt have major impact below 7cM

Question 19

When is mapping acccurate between 2 genes?

Answer 19

if distances are less than 7 cM

as only single cross overs can occur as interferance is complete.

declines above this due to occurance of undetected multiple crossovers and varying interference.

Question 20

What is: haldanes function kosambis function

Answer 20

haldanes function -no interferance kosambis function - interferance decreasing with distance

Question 21

What are the Recombination frequencies of:

• no cross over
• one cross over
• 2 strand double cross over
• 3 strand cross over
• 3 strand double cross over
• 4 strand double cross over.

Answer 21