Practice the genetic problems!!!
Gamete formation was in the last lab… it is important to be able to set up punnett squares.
At first we will assume that genes are inherited independently. In reality, chromosomes
are inherited independently but often genes are on the same chromosome, and are thus linked.
Mom ♀ (Bb)
Eye Color
Brown Eyes
Dad ♂ (bb)
Blue Eyes
B
B
b
Bb
Bb
b
Bb
bb
Take notice; gametes were formed for the one contribution from mother and one from the
father. Mother is on the top of the square since eggs are usually met by sperm. Much in the
same way, a line graph has the changing factor on the side, minor detail but important. Gametes
combine during recombination, fertilization, and one gene of each allele is combined. If you are
keeping up from the previous week, this is the establishment of the diploid state, 2n.
Dominant alleles are capital, recessive alleles are lowercase and each letter represents a
gene. You have two copies of every gene, one maternal and one paternal. Dominant expresses
over recessive. Homozygous has both of the same type of allele so homozygous dominant or
homozygous recessive. Heterozygous has one of each copy, but appears as the dominant
phenotype. The phenotype is the expressed trait… in the example, eye color.
So that is the basics. But there are sex linked traits. So there isn’t a whole lot of info on
the y chromosome; sorry guys! Since the sex of an individual will matter for sex linked crosses,
always write X with a superscript of the gene, X+ as an example. There are also lethal alleles,
usually recessive, so if an individual doesn’t have the other allele to compensate, you will never
see them. Draw the punnet square and cross out those individuals that would die in utero.
Incomplete dominance is when the heterozygous individual is a mix between the two extremes,
think red + white = pink. Codominance is when both alleles are expressed together, think about
blood types. Unfortunately blood type is a tricky one. Since O is recessive to both B and A we
write it as i. IB and IA are the ways to write B and A copies. So you know the genotype of O and
AB individuals but A and B individuals may be homozygous or have one i gene.
Please also practice making gametes. You have 2 copies of each gene but only pass off
one to your children, think meiosis! So again AaBBCCDD can possibly be ABCD or aBCD.
Review the examples and read the lab beforehand, it helps immensely and shows. If you have
questions still, come to office hours please. And remember the lab is due next week!
GeneticsProblemsfor Practice
In cats,the B allele codesfor black fur, andthe b allele codesfor yellow fur. The geneis locatedon the Xchromosome.However,the genotypeBb resultsin fur with a mottled appeaftmcecalledtortoise-shell.Suppose
a tortoise-shellfemaleis crossedwith a black qale.
mal What offspring would be expected?Would you expectany
,6
tortoise-shell males to be produced?
Yb
hr
t, O
I
x B- btqcl(
XB/
b
X lellov^)
x-vlxoy
fit^cl
'lodooe
I
Blac! /
fl
Tello,o
l,)uft'h''P
g
The allele "Au that enablesa personto tastethe chemicalPTC is dominantover the allele for the inability to
tastePTC. In addition,recall that the allele for brown eyes(B) is dominantover the allele for blue eyes@).
Supposetwo parents,eachwith the genotypeAaBb, havechildren. What proportionof thesechildrenwould be
blue-eyedtasten of PTC?What proportionwould be blue-eyednon-tasters?
A- l^slers
ffib
v
4 - r1Dyr-ht*'fs
B - Brurn elPS
ttueaf
AB Ab oB ^b 3l /6 1,rt+dt
A8
*h
b'- trlueeles
lgo i#r:l-
ob
pig that is homozygousrecessivehaswhite fur.
3. A dominantallele Tconfers blackfur on guineapigs.
Fred would like to know whetherhis pet black-flrred guineapig is homozygousdominantor heterorygous.
How might he useMendeliangeneticsto determinehis pet's genotype?
I ;,)
)A,sa
c)orr,nqnlirrAil
u
dvJ
&es/ cl^oss
fti{'
o_i$;-,.AR
3W
w
receg,le
'
u
u*'l * ")k^* t5 J5
*irffi,Lt\o
"u,tive'n,
"l
Plantsthat breedtrue for tallnessandalso for red flowers are crossedwith shon white-floweredplants. The
resultingF1generationconsistsentirely of tall pink-floweredplants.Assumingthe genesaxenot linked, predict
the offspring that would be producedin the Fzgeneration.
1A {r +R t(fR,
(r
{
^
F,,
7TR,r
3 tuAGtt
b P,rrK'trtll
,
t Qedthot{
A P,rt( 51Y.!
IR
all
z wr,e
,^lh;l<.thNr
iJI\(Y-
iC
t4.\
5. In humans,
normalskinpigmentation
is dueto a dominantallele"A". Albinism(thelackof r[ir, tffi5Ltatilfi
is dueto its recessiveallele "a". Supposea nomnl manwhosemotherwasalbino marriesa normal woman
whosefatherwasalbino. What arethe chancesthat thev will havean albino child?
A' no{nal
qlbr /uo
d '
#,
q
AAIM
Aalaq
Q{1,
I
U
d.
Blood typing hasbeenus,edas eridencein paterTry
( meanngfatherhood)cases,whenthe blood tlpe of the
motherandchild may indicatethata manaitiea
to be tne ruiirr.ouia.rot possiblehavefathered
the child. For
the following motherand,cfritacombinations,lndicate
which bloodgroup,ofpotentiarfatherswourdbe
exonerated.Tharis' which broodtype(s)*ourd
b" it p"rili;;;;idrr,",
to have?
Man exoneratedif he belongsto blood groups
/
b. O, 4
c.A
d. AB
e. B,O
7'
supposethat geneb is sex-linked,recessiveand le1h4!-when
it is
marriesa womanwho is heterozygousfor this g";;Trth;;;fi;L"" not maskedby the dominantallele. A man
manynormarchildren, what would be
thepredictedsexratio ofthesecliiArenf
XB Y,
;ur-f"'fro
8'
ag:1,/
x3
AII the offspring glodugedby crossing.red-flowered
plantswith white-floweredplantshavepink
flowers.
flower colors(and in whatpropottio;) would be
ro*o in trr" offspring i"
Jitrrc following crosses:
"".r,
RR-rnl,,
'o?'"0,-
-"0',1.0':
fffil
!,'::LlM
(
r l-Br
lrr I l(n/Rr,l
e'
f,: HfiYJil:$H*t#if;""j*|
nies,
ageneticist
d.j"ry'lg"
Berween
Aandc:rlo/o
crossing-over
berween
genes
occurred
in
Dsrwevu
Between
vcandD:4oo/o
{ruur
3:,ffi:il1,ili3i3/in","
T p",+L"s
l
*'fl"ffi,?ruin;l*"..
u""",
s.rr#n$ irrYc,Yo"r"
? A
qdA
qrn'v'q*s
"f
141,andsolidcolor(,f) is dominant
,9J
l0' In cockroaches'
blackcolor(B) is dominantto nro*n
cockroach
heterozygous
for boththesehaitsy"r::.*tF
:nXf"t#lT;J::::ffi:i
fi-LlaeK
i - -anwl,
7
) ,.1
ilS
S
to spotted(s). A
4 uro*n, spottediochoach. rt eyprooucehundre4s
of
ratio
istoutact<
sorid
:5ui".l-'p'ffii;ffiffi1 ,i!"il.f*,,spotted.
How
Lbss
rJO'"rs
Bbicxx "":
n, t!: #: #s . t:2
Bs BB 8B qtr65 5s
1;3:3;t elrych)e.a gB
65
Yrett
A t!;lr,tl,l,n,
8-sptt
EB BbSs IJ],tt
t
BtSt_663s f LSa
As Bb4 Abas\b4 [bag
w
l'
A fruit fly having a geno0pe of
ffis
what is the genotypicratio of the many.resultingoffspring?
ryd.
Z
L pe'rts n"kA h receJS'v
FT
{ FreI
1{.C,'IC€
, \\
t \
I
€tN
In peaplants,the allele for tallnessis dominantover the
allele for shortness.If you crossa plant that breedstrue
for shorfiresswith a heterozygousplant, what percentage
of the resurtingoifrpri.rj*o,itJi"
tiE!
"*p..r"a
-r-:'qll
f
f
5cz
+-5Aur4
+
X
gLorl
A man andhis wife both havenormalcolor vision, but a
daughterhasred-greencolorblindness,a sexIinkedrecessive
trait. Themansueshis wife for divorpeoo
fo*or ofinna"rity. can geneticsprovide
evidencequpportinghis case?
+
t'- fiotrtral
I
I
... r mal?
Y1e{ficll
a
X-
_X'
X-IX*y*lf.r-l
x'x- ;^"'";r^',;;'-prolw(
X ukbli;
v
Ca{fief le^o leE
Xy
Supposetwo genesarelinked, with genesw and
zon onememberof a homologouspair of chromosomesand p
andz on the othermember.tran inaivioual hasa g"notyp.
oi iihr,what
-sameteswould that individual
produceifcrossing-overdid occurbetweenthose
ivo g"i"ri
'rl
v),th
c fDsrtng ov((r l)ttlla7e il
5o
I
tl-
WWLZ
v
l
nelalel
}
Summer)qu4ru
uuruusr
squash4rc
areerrnertilnlre
eitherwhitetfyeltow.
or yellow, To
getw![e squash,at
To get
white. Theallelefor whichcororii oominantz"n*prffiyoi" rr*o,
;€
MalQ
u)h;lL
q
yellods CaA
receJl;,J4r two
i5
,
dh;lL
V
I
b+h
a{e
Tellow't^,
/- parcri{ aft
DPPDiltq
lo
t: ;l't ltt
*rh;#
Jrh,'/ni5 donitta'rr
6.
A womanwith type AB blood marriesa manhomozygousfor type
A blood, what could be the possible
blood typesof their children?
,t
t2
TN
-Lt
T'
TA
l
/
A+ lB
Tr^lT'f
7'
All the offsRrine.qrodycedby crossingred-floweredplantswith
white-floweredplantshavepink flowers.
what flower colo(s) (and in what proportionslwould be found in
the offspring ortr," rotio*iog cros.:
pink x
.n/'\
O
/) |
;q(-ke"(
.N
rT
'a
,I
r lUrlrr I
Rr-P|nR
r'r v)h;+L r tkQ\
,
tfa
,/a
^
P;nK
tDA,tz
A womanis a carrier for-a sex'linkedgenethat causesan embryoto
-- -'spontaneouslyabort. she hasnine
children.How manyof thesectrilaren$VE expgct!oU. Uoyri-
I"i': ti4nYa"!'J'3
a9:lD
/'Y
lnl
{
F-c*
-
aBer tke
Supposethat-indragons,the ability to breathefire is dueto a dominant
allele,andthe inability to breathe
fire (smolderingonly) is dueto itsrecessiveallele. The dominant
alleieof anothergeneis responsible
for
scaleson the dragon'sskin; its reces-sive
allelegivesa scale-less
.onaition. what genotypicand
phenotypicratios would be expectedfrom a cro-ssbetween
one smolderingscalelessdragonand one firebreathingdragonthat hasscales?
l"l; / :l
s,rolder,nl
Khlcl
; - ro
10. Thepercentage
of crossing-over
l{ue aft
[ (,,eL'lal
is L,iluozY1
'lrrlo ryof€-,.'
betweenfour linkedgenes(K, L,M &N) is asfollows: ....BerweenM andN: 8 %
Betweenr *a l: ffi
t;;;;
M andL: 19 Yo
BetweenKandN 5 %
BetweenNandL:ll%
What is the sequenceof geneson the chromosome?
,]-
h
5
fthe *W95
tl
Yl @KN ffiL
Al
b+hl: \