Unit 7- Linkage, Recomb, and Eukaryotic Gene Mapping

Question 1

Principle of Segregation

Answer 1

alleles at same locus of homologous pairs separate during meiosis

Question 2

Indep Assortment

Answer 2

alleles at one locus sort indep from alleles at another locus

Question 3

recombination

Answer 3

alleles sort into new combinations

Question 4

complete linkage

Answer 4

leads to nonrecombinants
- genes very close together and no crossing over

Question 5

crossing over with linked genes

Answer 5

leads to recombinants (at most half: a single crossover only affects 2 of 4 chromatids)

Question 6

calc recomb freq

Answer 6

of recomb progeny/ total # of progeny x100%

Question 7

coupling (cis config)

Answer 7

wild-type alleles are found on 1 chromo; mutant alleles are found on the other chromo
*mostly parental pheno

Question 8

Repulsion (trans config)

Answer 8

wild-type alleles and mutant allele are found on the same chromo
* mostly recomb pheno

Question 9

INTERchromosomal Recombination

Answer 9

crossing over between genes located on DIFFERENT chromosomes (due to indep assortment. Mendelian)

Question 10

INTRAchromosomal Recombination

Answer 10

crossing over between genes located on the SAME chromosome

Question 11

chi-square test of independence

Answer 11

1. Set up table of parents and their progeny (like a punnet sq) with row/column totals
2. calc expected: row total x column total / grand total)
3. sum of (O-E)^2 / E
4. d:f (# rows-1) x (# columns -1)

Question 12

Gene mapping with recomb freqs

Answer 12

• genetic maps determined by recomb freq (1 mu = 1%)
• map units: centiMorgans
  (as % goes up, so does distance)

Question 13

constructing a genetic map with the 3pt testcross

Answer 13

• more efficient mapping technique
• order of the 3 genes can be established in a single set of progeny
• some double crossovers can usually be detected
• provides more accurate map distances

Question 14

steps in determining gene order in 3pt cross

Answer 14

1. identify the nonrecomb progeny (2 most numerous)
2. Identify the recomb progeny (2 least numerous)
3. compare the pheno of double-crossover progeny with the pheno of nonrecomb progeny. (should be alike in 2 characteristics and differ in 1)
4. differing characteristic is encoded by the middle gene

Question 15

calc recomb freq

Answer 15

sum of all single and double crossovers/ total progeny

Question 16

coeff of coincidence

Answer 16

of obs double crossovers/ # of expected double crossovers

Question 17

interference

Answer 17

The degree to which one crossover interferes with
additional crossovers in the same region
1 - coeff of coincidence

Question 18

Poisson distribution

Answer 18

predicts the probability of multiple rare events

Question 19

mapping techniques

Answer 19

• mapping with molec markers (RFLPs)(variations in DNA sequence detected by cutting the DNA with
  restriction enzymes)
• Genome-wide association studies (associations w/in pops, haplotype, and linkage disequilibrium)

Question 20

genetic markers

Answer 20

variable genes with easily observable phenos for which inheritance could be studied
- ex: lower color, seed shape, blood types, and biochemical difference

Question 21

Physical-mapping methods are used to determine the physical position of genes on particular chromo

Answer 21

• somatic-cell hybridization
• deletion mapping
• physical mapping through molec anaysis (in situ hybridization)

Question 22

hetrokaryons

Answer 22

hybrid cells formed during somatic-cell hybridization (look for differing presence of chromo)

Question 23

Fluorescence in Situ Hybridization (FISH)

Answer 23

uses a single-stranded complementary DNA probe for the gene

Question 24

Recomb rates exhibit extensive variation

Answer 24

• among species
• among chromos of same species
• among males and females

Question 25

Walter Sutton’s Chromo Theory of Inheritance

Answer 25

genes are physically located on chromo

Question 26

Netti Steven’s and Edmund Wilson’s

Answer 26

sex was associated with specific chromo in insects

Question 27

Calvin Bridges’

Answer 27

nondisjunction of x chromo was related to the inheritance of eye color in Drosophilia

Question 28

Harriet Creighton and Barbara McClintock

Answer 28

interchromosomal recomb was the result of physical exchange between chromos

Question 29

linkage analysis

Answer 29

based on the detection of physical linkage between genes,
as measured by the rate of recombination

Question 30

genomewide association studies

Answer 30

looks for associations between traits and alleles in a POP

Question 31

haplotype

Answer 31

A specific set of linked alleles

Question 32

linkage disequilibrium

Answer 32

nonrandom association
between alleles in a haplotype

Question 33

single-nucleotide polymorphisms
(SNPs)

Answer 33

positions in the genome where people vary in a single nucleotide base

Question 34

deletion mapping

Answer 34

homo for mutation x hetero for deletion
- if trait in deletion area, 50% recomb
- if trait isnt in area, wild-type