Linkage and Chromosome Mapping (Lec 8 and 9)

Question 1

Genes located on the same chromosome that tend to be inherited together

Answer 1

Linked Genes

Question 2

T/F the closer together two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency

Answer 2

F, farther = higher probability

Question 3

A genetic map of a chromosome based
on recombination frequencies

Answer 3

Linkage Map

Question 4

T/F, map units indicate relative distance and order, not precise locations of genes.

Answer 4

True

Question 5

Indicate the positions of genes with respect to chromosomal features.

Answer 5

Cytogenetic Maps

Question 6

If crossing over takes place 28% of the time in the hybrid E f / e F, then what will be the frequency of the EF gamete?

Answer 6

The different gametes they can form are

EF, Ef, eF, ef.

Therefore,
28% * 1/4 = 7%

Question 7

In cotton, the dwarf red mutation (G = dwarf red, g = green) and the virescent mutation (V = non-virescent, v = virescent) were found to be 30 cM apart.

What are the expected frequencies of each gamete given the parent gamete GV/gv genotype.

Answer 7

30cM = 30%

30% = recombinants, since parents are GV and gv, the recombinants are gV and Gv, 30/2 = 15%

gV = 15% ; Gv = 15%

Therefore, 100-30= 70%
Two parents = 70/2

GV = 35% ; gv = 35%

Question 8

In cotton, the dwarf red mutation (G = dwarf red, g = green) and the virescent mutation (V = non-virescent, v = virescent) were found to be 30 cM apart.

Given Gamete frequencies:
gV = 15% ; Gv = 15%
GV = 35% ; gv = 35%

List the possible phenotypes and their frequencies.

Answer 8

Just multiply the frequencies for each combination of gametes, you should come up with

62.25% G_V_
12.75% ggV_
12.75% G_vv
12.25% ggvv

9 dwarf red, non-virescent
3 green, non-virescent
3 dwarf red, virescent
1 green, virescent

Question 9

Slow is dominant to rapid and silver is recessive to gold. Given the progeny counts below, how far apart are the gametes for the traits located from each other.

slow, golden - 58
rapid, golden - 7
slow, silver - 8
rapid, silver - 57

Answer 9

(8 + 7)/(58 + 8 + 7 + 57)
= 0.1154 = 11.54% = 11.54cM

Question 10

The inhibition of further crossover events by a crossover event in a nearby region of the chromosome is called _________

Answer 10

Interference

Question 11

This is a measure to assess the degree of interference between two crossover events in a particular region of a chromosome.

Answer 11

Coefficient of coincidence

Question 12

How is Coefficient of Coincidence calculated?

Answer 12

C = (Observed Double Crossovers)/(Expected Double Crossovers)

Question 13

Interference is calculated by?

Answer 13

I = 1 - C

Question 14

In the maize cross, the distance between v and pr is 22.3 map units, and the distance between pr and bm is 43.4 map units.

Given the following data:
NCO = 467
SCOab = 161
SCObc = 395
DCO = 86

What is the coefficient of coincidence and interference for these genes?

Answer 14

C = (DCOobs/DCOexp)
22.3mu = 0.223
43.4mu = 0.434
DCOexp = 0.223*0.434
DCOexp = 0.097 = 9.7%
DCOobs =86/1109=7.8%

C = 7.8/9.7 = 0.804
I=1 - 0.804 = 0.196

19.6% fewer DCOs occured than expected

Question 15

T/F I<1 means that there is fewer percent DCOs occuring

Answer 15

True

Question 16

Short cuts for pedigree analysis: Autosomal Dominant

Answer 16

Affected parents can have unaffected children

Question 17

Short cuts for pedigree analysis: Autosomal recessive

Answer 17

Unaffected parents can have affected children

Question 18

Short cuts for pedigree analysis: X-Linked Dominant

Answer 18

Affected fathers will always have affected daughters and never affected sons.

Question 19

Short cuts for pedigree analysis: X-Linked recessive

Answer 19

Affected mothers will always have affected sons; otherwise, 50-50 in male offspring of normal female.

Question 20

Short cuts for pedigree analysis: Y-Linked

Answer 20

Father to son only

Question 21

Short cuts for pedigree analysis: Maternally inherited

Answer 21

Affected mother to children only. Expressed phenotype of child depends on the genotype of the mother.

Question 22

Short cuts for pedigree analysis: A trait is dominant if

Answer 22

It doesnt skip a generation

Question 23

Short cuts for pedigree analysis: A trait is recessive if

Answer 23

It can skip a generation

Question 24

What is a proband?

Answer 24

The first individual to be investigated

Question 25

Short cuts for pedigree analysis: Mitochondrial genes

Answer 25

If affected female, all children inherit it

If affected male, none of the children inherit it

Dominance is not an issue because only one allele present in each individual

Question 26

In the shortcut for mitochondrial genes, why is it that only children of affected female and not male inherit it.

Answer 26

Because mitochondria can only be inherited from the mother.

Question 27

Out of questions, will try to add soon.

Answer 27

Henlo