Chapter 14: Genetic Mapping in Eukaryotes Flashcards Preview

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Flashcards in Chapter 14: Genetic Mapping in Eukaryotes Deck (27):
1

Syntenic?

genes that are on the same chromosome

2

Linked genes?

- genes on the same chromosome that do not seem to assort independently
-loci that are on the same chromosome
- inherited together and do not assort independently
- these genes belong to a linkage group
#linkage groups = # chromosomes

3

Genetic recombination?

the process by which recombinants are produced ( progeny showing non parental combinations of alleles)

4

Genetic recombination
L> An exchange event between?
L>reshuffling of?

homologous chromosomes
- alleles
L> daugther chromosomes carry combos of alleles not present in parental chromosomes ...aka recombinants

5

Genetic recombination:
Parentals?

- progeny showing parental combination of alleles...aka non-recombinants

6

Genetic recombination:
-recombinants?

- progeny showing non-parental combination of alleles ...aka non-parentals
- crossing over occurs here
L> two homologous chromosomes line up...
chromatids...breakage and crossing over occurs...reunion: exchange is complete...recombinants have formed

7

Hz(frequency) of recombination:
-The Hz of crossing over between two linked genes is ?

proportional to their location on the chromosome
L> the closer the genes are the less likely there is going to be any crossing over...the farther away they are the more crossing over will occur in that region.

8

Hz(frequency) of recombination:
-interlocus distance?

the percentage of recombinant offspring produced between two loci and is defined as the interlocus distance

9

Hz(frequency) of recombination:
- 2% recombination = what in map units or centimorgans?

- 2 map units (mu)
- 2 centimorgans (cM)
**0.002 frequency of recombination

10

Linkage ratio?

if two linked loci are far enough apart the # of recombinants will be approximately 50%
- there would be a 1:1:1:1 ratio for all four phonos

11

Are the loci involved in linked genes different or similar to those seen in unlinked genes?

L> these loci are indistinguishable from unlinked genes

12

Linked Autosomal Genes
1. Cross wild-type parent with non wild type parent.
a+b+/a+b+ x ab/ab

F1: a+b/ab

13

Linked autosomal genes:
2. Cross a+b+/ab x ab/ab (test cross)

Parental progeny:
a+b+/ab (wild type).... ab/ab
Recombinant progent:
a+b/ab ab+/ab

14

What is the formula for map distance?

map distance = (# recombinant progeny/total # progeny) x 100

15

Nomenclature for synteny:
double heterozygote for w and m alleles, label if they are trans or cis!
- w+m+/wm
- w+m/wm+

- cis ( when two dominant alleles are on one homolog and the two recessive mutant alleles are on the other homolog...aka coupling)
- trans ( each homolog carries the dominant allele of one gene and the mutant allele of the other gene, called repulsion)
- crossing over of cis loci = w+m and wm+ recombinants
- crossing over of trans loci= w+m+ and wm recombinants

16

Order of linked genes:
- Explain the three point test cross approach!

- tripe heterozygote crossed with a triple homozygote recessive
- note the phenotypic classes seen in progeny
L> 2 ^n = phenotypic classes
- single and double crossovers to consider

16

Order of linked genes:
- Explain the three point test cross approach!

- tripe heterozygote crossed with a triple homozygote recessive
- note the phenotypic classes seen in progeny
L> 2 ^n = phenotypic classes
- single and double crossovers to consider

17

Recombination Hz for linked genes:
- whats the formula?

(Single cross over region (w+x) + double cross over region (#+#)/ total progeny )100
**this also = map distance

17

Recombination Hz for linked genes:
- whats the formula?

(Single cross over region (w+x) + double cross over region (#+#)/ total progeny )100
**this also = map distance

18

Whats the formula for the total map distance when examining recombination Hz for linked genes?

(single crossover region (w+x) + double crossover (#+#) + single crossover region (y+z) + double crossover (#+#)/ number of progeny)100

18

Whats the formula for the total map distance when examining recombination Hz for linked genes?

(single crossover region (w+x) + double crossover (#+#) + single crossover region (y+z) + double crossover (#+#)/ number of progeny)100

19

Interference:
- what is this expressed as?
- what is interference?
L>underestimation of what?

- expressed as coefficient of coincidence
- when one crossover event interferes with a second crossover event
- an underestimation of the number of double crossovers

19

Interference:
- what is this expressed as?
- what is interference?
L>underestimation of what?

- expressed as coefficient of coincidence
- when one crossover event interferes with a second crossover event
- an underestimation of the number of double crossovers

20

Formula for interference? (cc)

cc= observed double crossover Hz/ expected double crossover Hz
....Interference = 1-cc
If cc= 1 then there is no interference and all double crossovers were observed..

20

Formula for interference? (cc)

cc= observed double crossover Hz/ expected double crossover Hz
....Interference = 1-cc
If cc= 1 then there is no interference and all double crossovers were observed..

21

Interference example:
- expected # of double crossovers = 0.208(0.1)
- observed double crossovers= 6/500
L> what is CC?
L> whats the interference?
L> explain answer

cc= 0.023/0.0308= 0.577
interference= 1-0.577= 0.423
cc does not equal interference...
Therefore, in this case, only 57.7% of the double crossovers were observed.

21

Interference example:
- expected # of double crossovers = 0.208(0.1)
- observed double crossovers= 6/500
L> what is CC?
L> whats the interference?
L> explain answer

cc= 0.023/0.0308= 0.577
interference= 1-0.577= 0.423
cc does not equal interference...
Therefore, in this case, only 57.7% of the double crossovers were observed.