Unit 7 - Gene Mapping and Linkage

Question 1

Synthetic Genes

Answer 1

*Genes located on the same chromosome

Question 2

Linked genes

Answer 2

*when synthetic genes are very close togeather their alleles cannot sort independantly
*these are called linked genes

Question 3

Recombanant genes (2)

Answer 3

*Alleles of synthetic genes can be reshuffeled when crossing over occurs = recombanant genes
*Homologs that do not reshuffle alleles are called parental chromosomes

Question 4

Gene linkage and gametes (3)

Answer 4

*Genetic linkage leads to the production of significantly more gametes with parental allele combos.

*This is beacuse crossing over is much less likley to occur wwith linked genes

*therefore we can detect linked genes by looking for hieghtened parental allele frequencies

*For example, a dihybrid AaBb with unklined genes will produce four gamete combos in equal frequency (AB, Ab, aB and ab, 25% each) but if A and B are linkede then the parental combos will occur much more (AB and ab >50% when paretns are AABB and aabb)

Question 5

Complete Genetic linkage (3)

Answer 5

*When there is no crossing over due to linked genes; only parental gametes are formed

*male fruit flies display this

*For example a homo dom (AABB) and homo recess (aabb) only produce AB and ab gametes

Question 6

Incomplete genetic linkage (3)

Answer 6

*Much more common than complete linkage

*Parental combos occur more frequantly, but in equal proportions to eachother.

*for example, a gamete will have a parental combo (AB or ab) 70% of the time, but AB and ab each appear 35% of the time

Question 7

Recombination frequency (2)

Answer 7

R = #of recombanants / total number of children

*If the R < 50% the tested genes are linked

Question 8

Recombination frequency and gene distance (2)

Answer 8

*Crossing over occurs more frequently between genes that are far appart, and at a lower rate when close togeather

*i.e. the higher the recombination frequency the farther apart two genes are

Question 9

Map Units (2)

Answer 9

Recombination frequencies between two genes can be converted into units of physical distance; called map units (m.u.)

*1% recombination frequency = 1 m.u.

Question 10

Chai Squared and gene linkage

Answer 10

Expected results follow a 1:1:1:1 ratio, n is the number of combonations - 1