Lecture 16

Question 1

chromosomes

Answer 1

are the unit of transmission in meiosis, not genes
- genes are on chromosomes

Question 2

linked genes

Answer 2

can not undergo independent assortment

Question 3

crossing over frequency

Answer 3

frequency of crossing over on a single chromosome is proportional to distance between them

Question 4

recombination

Answer 4

crossing over result

Question 5

chromosome maps

Answer 5

indicate relative location of genes on chromosomes

Question 6

meiotic sequences - independent assortment

Answer 6

no linkage exhibited

Question 7

complete linkage

Answer 7

linkage without crossing over
- no crossing over between two genes
- produces parental (non-crossover) gametes

Question 8

recombinant crossover

Answer 8

linkage with crossing over

Question 9

crossing over

Answer 9

• occurs between 2 non-sister chromatids
• both parental and recombinant (crossover) gametes are produced
• occurs between homologous pairs

Question 10

linkage ratio

Answer 10

• complete linkage between two genes due to proximity (the closer the more of a link)
• unique F2 phenotypic ratio resutls

Question 11

linkage group

Answer 11

• genes on the same chromosome are part of linkage group
• number of linkage groups should correspond to haploid number of chromosomes

Question 12

chiasmata

Answer 12

• synapsed chromosomes in meiosis wrap around each other
• area of crossing over
• X-shaped intersections with points of overlap (points of genetic exchange)

Question 13

chiasma

Answer 13

• percentage offspring resulting from recombinant gametes depends on distance between 2 genes on same chromosomes
• two genes located close to each other along a chromosome are less likely to have chiasma

Question 14

sturtevant

Answer 14

• complied data from crosses
• recombination frequencies between linked genes are additive

Question 15

because a chiasma occurs…

Answer 15

crossing over is the event

Question 16

map unit (mu)

Answer 16

• 1% recombination rate between two genes on chromosomes
• also called centi-Morgans (CM)
• relative distances, not exact ones
• can help to decide the likely hood that there would be a recombinant event between 2 genes

Question 17

single crossover (SCO)

Answer 17

• occurs between 2 non-sister chromatids
• recombination is observed in 50%
• in genes 50 map units apart, crossing over can be expected between 100% of tetrads

Question 18

closer genes…

Answer 18

do not split during recombination

Question 19

farther apart genes…

Answer 19

are likely to split during recombination

Question 20

single exchange between 2 non-sister chromatids in tetrad stage

Answer 20

• 2 non-crossover (parental) gametes produced
• 2 crossover (recombinant) gametes produced

Question 21

single crossovers…

Answer 21

used to determine distance between 2 linked genes

Question 22

double crossover…

Answer 22

• double exchanges on genetic material
• used to determine distance between three linked genes
• genes must be heterozygous for 2 alleles

Question 23

3 criteria of 3-point mapping

Answer 23

1) parent must be heterozygous for all three genes under consideration
2) phenotypic class must reflect genotype of gametes of parents
3) sufficient number of offspring must be produced for representative sample

Question 24

non-crossover F2 phenotypes

Answer 24

• occur in greatest proportion of offspring

Question 25

double-crossover (DCO) phenotypes

Answer 25

occur in the smallest proportion of offspring

Question 26

reciprocal classes of phenotypes

Answer 26

- F2 phenotypes complement each other - derived from heterozygote - have a wild type and mutant for all three genes

Question 27

single cross over event is more likely than a...

Answer 27

double cross over event

Question 28

no cross over event is more likely than a...

Answer 28

single cross event

Question 29

Determining gene sequence: Method 1

Answer 29

based on three possible arrangements of genes

Question 30

Determining gene sequence: Method 2

Answer 30

uses 3 possible arrangements, also considers double-crossover event