Topic 6: Gene Mapping and Linkage

Question 1

_____________ won the Nobel Prize in physiology/medicine in 1933

Answer 1

Thomas Morgan

Question 2

Thomas Morgan’s work validated which three foundational theories?

Answer 2

Chromosomal Inheritance theory
Genes ae physical entities that are integral on chromosomes
Closely related species have similar number and arrangement of chromosomes

Question 3

when does homologous recombination occur?

Answer 3

prophase I of meiosis

Question 4

homologous recombination results in…

Answer 4

recombinant chromosomes (non-parental chromosomes)

Question 5

________ & _________: chromosomes that do not cross over retain all the same alleles as the parent chromosomes

Answer 5

parental chromosomes
nonrecombinant chromosomes

Question 6

_______ genes: genes that are located on the same chromosome

Answer 6

syntenic genes

Question 7

what happens when syntenic genes are located closely together?

Answer 7

alleles may be unable to independently assort, resulting in genetic linkage (!)

Question 8

true/false: syntenic genes that are very far apart do assort following Mendel’s law of Independent Assortment

Answer 8

true

Question 9

true/false: linked genes do not assort independently

Answer 9

true!

Question 10

true/false: linked genes are always syntenic

Answer 10

true!

Question 11

true/false: linked genes don’t cause less recombinant gametes made

Answer 11

false!

Question 12

genetic linkage leads to _____ number of parental gametes than recombinants (compared to independent assortment)

Answer 12

greater/higher

Question 13

if unlinked, genes produce ______ genetically different gamete combinations in a ratio of….

Answer 13

four
1:1:1:1

Question 14

________: no recombination at all occurs between linked genes

Answer 14

complete linkage

Question 15

_______: resulting recombination between the homologs produces a mixture of parental and recombinant gametes

Answer 15

incomplete linkage (this is way more common than complete linkage!)

Question 16

if we have a dihybrid cross with incomplete linkage, what kinds of gametes will be produced?

Answer 16

two parental gametes
2 recombinant gametes
(but these are not produced in equal amounts, parental will have frequencies of >50%, recombinants <50%)

Question 17

what is the formula for the recombination frequency? (rate of recombination of syntenic genes)

Answer 17

r = number of recombinant offspring/ total number of offspring

Question 18

1. Crossing over occurs ar a higher rate between genes that are further apart than those closer together
2. Linked genes with higher recombination frequencies are more distant from each other than other linked genes with lower recombination frequencies

are two interpretations to which idea?

Answer 18

recombination frequency, the two ways to interpret the equation!

Question 19

Who are the three men behind the discovery of genetic linkage? what did they study?

Answer 19

William Bateson and Reginald Punnett (studied sweet peas, and saw that the offspring didn’t have a traditional 9:3:3:1 dihybrid ratio)

Thomas Morgan confirmed genetic linkage and indirectly constructed one of the first genetic maps in 1911

Question 20

which three people came up with cytological evidence of recombination?

Answer 20

Harriet Creighton and Barbara McClintock in 1931 (corn)

Curt Stern (drosophila)

Question 21

true/false: in genetic linkage mapping,
smaller recombination freq. indicated genes were closer together
larger recombination freq. indicated genes were further apart

Answer 21

true!

Question 22

Alfred Sturtevant proposed the first….

Answer 22

genetic linkage map!

Question 23

what does m.u stand for?

Answer 23

map units

Question 24

what does cM stand for?

Answer 24

centi-Morgan

Question 25

1% recombination = ____________ between genes

Answer 25

1 map unit between genes

Question 26

what kind of test do we use to calculate recombination frequency between two linked genes?

Answer 26

two-point test crosses

Question 27

what kind of test do we use to identify genetic linkage between 3 genes?

Answer 27

three-point test cross, provides data for determining recombination freq. between linked genes

Question 28

three genes in a three-point test cross results in ______ genetically different genotypes from each parent

Answer 28

eight

Question 29

true/false: “parental” and “recombinant” are relative to the trihybrid organism

Answer 29

true! the double crossover of one parental may be the original genotype of the other parental!

Question 30

when viewing raw data of genetic linkage, the largest numbers represent…
the smallest numbers represent…

Answer 30

overrepresented parental phenotypes

double crossovers

Question 31

Rollins Emerson studied genentic linkage using 3-pt. test crosses using what….

Answer 31

corn

Question 32

chiasma ____________ (I): reduction in the observed number of DCO’s relative to the number expected if the two SCO’s happened independently

Answer 32

interference,
indicates the influence of some process(es) that limit the number of crossovers in short length chromosomes

Question 33

what is the formula for the coefficient of coincidence (c)? (!)

Answer 33

observed DCO / expected DCO

Question 34

negative interference is when…

Answer 34

I < 0, zero is larger than our interference

Question 35

true/false: map distances often underestimate the physical distance between genes

Answer 35

true!

Question 36

heterogametic organisms have _______ recombination in general

ex: male mammals (XY)
female birds (ZW)

Answer 36

lower

Question 37

true/false: in humans, genetic recombination is more frequent in females!

Answer 37

true (larger recombination map)

Question 38

what do hotspots and coldspots mean in terms of genetic linkage?

Answer 38

hotspots: recombination happens more frequently than expected based on # of nucleotides present
coldspots: recombination happens less frequently than expected based on # of nucleotides present