Topic 4 Linked Genes And Chromosome Mapping

Question 1

What does it mean for genes to be linked

Answer 1

When the alleles of two different genes do not assort independently and are seen at differing frequencies from 1:1:1:1 ratio

They are close enough to each other to disrupt independent assortment

Question 2

What are genes on the same chromosome called?

Answer 2

Syntenic

Question 3

What is cis conformation of alleles

Answer 3

WT alleles on same homolog

a+b+/ab

Question 4

What is trans confirmation of alleles

Answer 4

WT alleles on diff homologs

a+b/ab+

Question 5

What is RF

Answer 5

Recombinant factor, % of recombinants in progeny
If RF is 0.3, 70% of progeny is parental
Measured in centimorgans (cM)

Question 6

What is a chiasmata

Answer 6

Cross shape that forms during meiosis when two dyads form a tetrad (bivalent)
(Cross over)

Question 7

If linked gene are further apart, the change of crossing over is ____

Answer 7

Higher
And vise versa

Question 8

Formula for RF

Answer 8

RF= total recomb/total offspring

Times 100 to get percent

Question 9

why do we use a three gene test cross

Answer 9

To determine gene order
And relative distance of all three genes

Question 10

What is the equation to find how many gametes a cross makes

Answer 10

2^n
For n= number of genes

Question 11

How do you find the order of linked genes from a three gene test cross

Answer 11

Take RF and which ever value is largest is the two genes furthest apart.

Question 12

For gene test crosses the offspring with the most observed number with specific genotype, that genotype is ____
Ones with least observed is

Answer 12

Parental
Double crossovers

Question 13

What do you do for recombination frequncies for double crossovers

Answer 13

Count the observed number of offspring with the DCO twice then recalculate RF.

Question 14

How to find the middle gene using the dco and parent genotypes

Answer 14

Which ever gene flips in the DCO when compared to parental is the middle gene

Ex Parental: Abc aBC
DCO: AbC aBc

Question 15

How to calculate coefficient of coincidence (c)

Answer 15

Observed DCO/Expected DCO

Question 16

How to calculate interference (I)

Answer 16

(1-c)x100

Question 17

What does the answer from interference tell us

Answer 17

The percent of DCO prevented by interference

Question 18

How do you determine map distance for genes greater than 50cM apart

Answer 18

Add more genes and find distance between them and original genes to find accurate measure of distance

Question 19

1cM is how many base pairs

Answer 19

1 million

Question 20

What is null hypothesis when carrying out chi test for linkage

Answer 20

The genes are not linked

Question 21

What are the steps to finding if genes are linked using the efficient way

Answer 21

1. Set up cross between genes and fill in given values
2. Calculate the frequency of each gene (fA= total A/total offspring)
3. Multiply that frequency by the frequencies of the corresponding squares in the box and by total off spring to get expected count of each genotype
4. Use chi square test normally but with new expected values with DF 1

If linked, RF is what you thought