Chapter 7

Question 1

_______ student of T.H Morgan, generated the first map of chromosome based recombination frequency. He postulated that frequency of recombination could be used to determine the physical distance separating the genes on a chromosome

Answer 1

• Alfred Henry Sturtevant

Question 2

______ suggested that genes on same chromosomes segregated together, also those closely linked were rarely subject to recombination

Answer 2

• T.H Morgan

Question 3

Principle of segregation

Answer 3

• each diploid individual possesses 2 alleles that separate during meiosis, one allele to each gamete
• each allele is at the same position on a homologous chromosome

Question 4

Principle of Independent assortment

Answer 4

• two alleles separate independently of alleles at other loci

Question 5

Chromosome theory of heredity

Answer 5

• Sutton, genes are found on chromosomes

Question 6

Linked Genes

Answer 6

• those that are close together on the same chromosome travel together during meiosis and do not usually sort independently

Question 7

What is responsible for recombination?

Answer 7

• the switching of genes from one homologous chromosome to another
• genes that are normally linked now sort independently

Question 8

Single Crossover leads to what

Answer 8

• half recombinant half nonrecombinant

Question 9

Crossing over can occur in in what type of chromosomes?

Answer 9

• nonsister/nonhomologous chromatids

- if occurred between sister chromatids no genetic difference would occur in products

Question 10

__________ maize, cytological markers and 2 linked genes. Showed crossing over results from a physical change between homologs

Answer 10

• Harriet Creighton and Barbara McClintock

Question 11

Recombination frequency formula

Answer 11

=(# of recom progency)/(total #of progency) x100

Question 12

Coupling (cis)

Answer 12

• wild type alleles on one chromosome/mutant on other

Question 13

Repulsion(trans)

Answer 13

• each chromosome has one wt and one mutant

Question 14

If genes are completely linked (no crossing over) what results?

Answer 14

• only nonrecombinant are produced

Question 15

If genes assort independently what results?

Answer 15

• 1/2 are recombinant, 1/2 nonrecombinant

Question 16

With linked genes and some crossing over what is predominant?

Answer 16

• nonrecombinant

Question 17

Independent Assortment allows genes to be

Answer 17

• on different chromosomes, combine randomly

Question 18

Completely linked

Answer 18

• on same chromosome, close together so crossing over is rare

Question 19

Incomplete linkage

Answer 19

• genes on same chromosome, but some distance apart allows for some recombination

Question 20

Interchromosomal recombination

Answer 20

• between genes on different chromosomes, arises from independent assortment on sister chromatids anaphase 1 of meiosis

Question 21

Intrachromosomal recombination

Answer 21

• between genes on the same chromosome, crossing over between nonsister chromatids in prophase 1 of meiosis

Question 22

Genetic maps

Answer 22

• use recombination frequency to make chromosome maps

- distances are in terms of map units (1% of recomb freq, or centimorgans cM)

Question 23

Gene mapping with recomb frequency rules

Answer 23

1. recomb freq cannot be > 50% for two genes
2. 50% is the freq of recombination for genes on different chromosomes, so impossible to discern between two genes that are far apart on same chromosome and those on different chromosomes
3. genes that are far apart can undergo DOUBLE crossovers (its as if the crossover never occured)

Question 24

Two point test cross

Answer 24

• test cross between 2 genes

Question 25

Linkage groups

Answer 25

- distant markers can be tied together by intermediate markers - intermediate markers allow a linkage group to span greater than 50cM distance

Question 26

Why are three point crosses better than 2 point crosses?

Answer 26

1. order of genes can be established in a single cross | 2. double crossovers can be detected

Question 27

What does a double crossover yield?

Answer 27

- recombinant chromosomes with altered middle genes

Question 28

what is a map unit equal to

Answer 28

- 1% recombination | - so if 10%=10 map units

Question 29

Nonrecombinants are the ____ numerous

Answer 29

- most

Question 30

Double crossovers are the ____ numerous

Answer 30

- least

Question 31

How do we compare observed numbers to expected ?

Answer 31

- the probability of double cross occurring can be calculated by the probability of two single crossovers multiplied together Exp=(RF1xRF2) x total # observations -decimals not percents

Question 32

Interference

Answer 32

- when the incidence of a crossover affects another crossover

Question 33

Negative interference

Answer 33

- increases the chances of another crossover | - More observed DOCS occurred than expected

Question 34

Positive interference

Answer 34

- reduces the chances of another crossover taking place | - less observed DOCs occurred than expected

Question 35

coefficient of coincidence formula

Answer 35

COC= #obs crossovers/# expected crossovers

Question 36

Interference formula

Answer 36

Intf=1-COC x100 | - answer means that whatever % you get of double crossover progeny expected will NOT be observed

Question 37

If interference is 1, how many double crossovers will you get?

Answer 37

- zero crossovers

Question 38

Recombination hot spots

Answer 38

- areas where recombination occurs more than expected | - more recombination in females bc no crossing over occurs in males

Question 39

Restriction fragment length polymorphism (RFLP)

Answer 39

- changes in DNA sequence that modify restriction enzyme recognition sites

Question 40

Variable number of tandem repeats (VNTR)

Answer 40

- differences in copy number | - SSLP, minisatellite, microsatellite

Question 41

Single Nucleotide polymorphism (SNP)

Answer 41

- a single base change

Question 42

Types of molecular markers

Answer 42

1. Restriction fragment length polymorphism (RFLP) 2. Variable number of tandem repeats (VNTR) 3. Single Nucleotide polymorphism (SNP)

Question 43

Microsatellite markers

Answer 43

- di, tri, tetra nucleotide repeats - polymorphic repeats of 2-4 base pairs - codominant

Question 44

If two chromosome genes are completely linked what is the expected F2 phenotype? genotype?

Answer 44

- 3:1 phenotype | - 1:1 genotype

Question 45

If independent assortment occurs what will be the phenotypic ratio?

Answer 45

- 1:1