Lesson #8 Gene Mapping
AGRO 315 Genetics
Questions due Monday, March 5, 2012, 11:59 pm
1. Marker Assisted Selection in Cattle
a. Fill in the question 1 square above, 10 map units between the B,b and F,f loci means
that the percent of parental gametes from BbFf cow is…
b. The color to select among the test cross calves above if you want to raise lean cattle
is….
c. Bf / bF cattle are in
cis
trans
d. I want to raise lean cattle so in the BF / bf X
____ black
____ red
bbff cross I would select….
_____ it does not matter since ½ are ff
2. Mapping Mysterious Mouse Genes:
A hard working group of UNL animal geneticists mapped a gene in mice that causes
juvenile blindness. Let’s tell their story with this problem.
Part 1: Some mice in a family were found to have cataracts. Their first crosses with
these blind mice showed that a single gene controlled the trait and blindness was
recessive.
a. The F2 family ration of normal to blind must have been ________
There next experiment was to set up a test cross.
Bb : normal vision but carry the blind allele
Tt: Black but carry the albino allele
The cross BbTt X bbtt was then performed to generate these testcross offspring.
Offspring:
Blind, albino
182
Blind, colored
18
Normal, albino
22
Normal, colored 176
398
:
b.) Why could they tell that the blind gene was on the same chromosome as the albino
gene from this result?
c. ) Calculate the map distance from the B,b to T,t loci from this data.
d.) Based on this result, what are TWO possible map unit distances between the B,b
locus and the Fes locus that is mapped to mouse chromosome 7 (Go to the mouse
genome link on Blackboard)
e.) The mouse lab in the UNL animal science department continues to do research on
this blindness trait. Go to the pictures taken recently of three mice families that are on
our Blackboard site and match the family picture with the cross Punnet square diagrams
below.
Cross #1 is….. A B C
Cross #2 is ……. A
B
C
Cross #3 is ……A B C
tB
Tb
tb
TB
tb
tb
Tb
tB
tB
tb
A
TB
Tb
tB
tb
B
TB
Tb
T_ : black
tt: white
tB
B_: sighted
bb: blind
tb
C
f. Which family could the UNL gene mappers NOT use to estimate the T,t to B,b map
distance because NEITHER parent is able to make recombinant gametes that are
crossovers between the T,t and B,b loci and detectable?
___ cross #1
___ cross #2
___ cross #3
g. Draw a picture that show the chromosomes of the parents from this cross and be
ready to explain why you cannot map from following thes
3. Human genome mapping
Gene mapping in humans requires cooperation among geneticists, doctors and many
families. The data sets provided in this lab represent information similar to what human
geneticists would obtain to map genes onto human chromosomes. The following traits
have been examined.
Phenotype
Genotype
Normal X-chromosome XFXF, XFXf ,
XFY
Fragile X
XfXf ,XfY
Phenotype
Normal fat metabolism
Phenotype
Genotype
H
Normal blood clotting X XH, XHXh,
XHY
Bleeding disease
XhXh,XhY
(hemophilia B)
Phenotype
.
Normal immune system XIXI, XIXi,
XHY
i
SCID
X Xi, XiY
adrenoleukodystrophy
(ALD)
Genotype
XAXA, XAXa,
X AY
XaXa, XaY
50 sons of females with the genotype FH/fh (XFHXfh ) have the phenotypes below:
Son’s phenotype
Normal X chromosome, normal blood clotting
Fragile X, normal blood clotting
Normal X, hemophilia B
Fragile X, hemophilia B
Number Mom’s gamete?
21
2
2
25
a) Indicate the genotype of the gamete the mom donated to each type of son by filling
in the table above.
b) Explain why we do not need the father’s phenotype in these crosses to map these
loci.
c) Determine the genetic distance between the F and H loci.
d. Color blindness is not a disease but is an X-linked trait. The gene for color blindness
is recessive (b) and the normal color vision allele is dominant (B). Geneticists find
women who are heterozygous at the A,a; B,b and I, i loci and all had the same
arrangement of these genes on their X chromosome. They determine the phenotypes
among the 248 sons of these trihybrid women and from this deduce the following:
Trihybrid women’s
gametes
ABI
ABi
AbI
Abi
aBI
aBi
abI
abi
Number
8
84
24
2
4
34
82
10
a. Use this data to map the A,B and I loci.
e. Place the color blind locus on the map above.
f. Explain why the hemophilia A trait is independent of the DMD trait, even though the
genes controlling these traits are on the same chromosome.
4. Gene mapping in Corn
Thousands of acres in Nebraska have high pH soils. Some corn hybrids grow very
poorly in these soils because of iron chlorosis. There is Fe in the soil, but the corn plant
cannot extract it with the high pH.
Some hybrids have the ability to grow well in these high pH soils. There is a mysterious
gene that controls this ability. Because a breeder needs to be able to select offspring
with the desired gene, even under normal pH soils, some seed companies are trying to
map, then discover the identity of the high pH tolerance gene. The mapping is done
with DNA markers, little segments of DNA that are copied from a specific locus and can
be tracked from parents to offspring with a technique called electrophoresis (we will
learn about this after exam #2).
A. Use the data below to map these three loci. F,f is the high pH tolerance gene, Plant
that are F_ tolerate the high pH (are green), ff plants get the Fe deficiency phenotype
(see link to Blackboard) A,a; B,b; D,d, E,e and G,g are DNA markers.
Cross #1 AaBbFf X aabbff
Gamete from the trihybrid:
ABF
24
ABf
84
AbF
1
Abf
141
aBF
143
aBf
2
abF
83
abf
22
500
Map the A,a ; B,b and F,f loci
B. Cross #2 AaEeFf X aaeeff
Gamete from the trihybrid:
AEF
24
AEf
42
AeF
3
Aef
182
aEF
193
aEf
2
aeF
33
aef
21
500
Map the A,a ; E,e and F,f loci
C . Cross #3 DFG / dfg
X ddffgg
Gamete from the trihybrid
DFG
102
DFg
24
DfG
23
Dfg
99
dFG
100
dFg
27
dfG
26
dfg
98
500
Map the D,d ; F,f and G,g loci
4. D. Draw a map that represents what you have discovered from your mapping.
4.E. Which DNA marker will most help a plant breeder select for high pH tolerance even
in normal pH soils.
5. Tracing Genealogy The X and Y chromosomes pair in males during meiosis
because of the psedoautosomal regions at the ends of the Y chromosome.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/SexChromosomes.html
Explain…
…………. why it would be difficult to determine a linkage map for most of the loci on the
Y chromosome. Use the term, “crossing-over”, in your answer.
….how recent DNA analysis could be performed to test the hypothesis that Living
relatives of Sally Hennings, a slave of Thomas Jefferson, were actually President
Jefferson’s relatives.
……why is the Y chromosome more valuable than the X in tracing long term
genealogy? Use the terms “crossover” and “recombination” in your answer.
…… If you have a Y chromosome, name three people in the world today who should
have the same Y chromosome as you.