Sex-Influenced (Autosomes)
P Horned x
Hornless
HH
H'H'
H
H'
F1 Horned x
Hornless
HH'
HH'
1/2 H 1/2 H' 1/2 H 1/2 H'
F2
Genotypes
Phenotypes
_______
_______
1/4 HH
Horned
Horned
2/4 HH'
Horned
Hornless
1/4 H'H'
Hornless Hornless
F2 genotypic ratio - 1:2:1
F2 phenotypic ratio - 3:1 - Horned:hornless
- 1:3 - Horned:hornless
H - horned - dominant in males
H' - hornless - dominant in females
.
155
Sex-influenced dihybrid cross
B = bald
B′ = haired
F = long index finger length
F′ = short index finger length
♂
bald
haired
♂
♀
BB
BB′
bald
haired
♀
long index fingers
short index fingers
B′B′
B is dominant in
B′ is dominant in
FF′
F′F′
♂
♀
Heterozygous bald man,
with long index fingers
BB′ FF
FF
long index fingers
short index fingers
F is dominant in ♀
F′ is dominant in
X
X
♂
Bald woman, heterozygous
for long index finger length
BB FF′
B
B
BB
B′
BB′
B
BB
BB′
1/2 ♂
1/2 x 1/2 x 1/1 = 1/4
P.R. = 1:1:1:1
F′
FF′
FF′
1/2 bald, 1/2 haired
1/1 long index fingers
♂ with long index fingers
bald ♂ with short index fingers
bald ♀ with long index fingers
haired ♀ with long index fingers
1/2 x 1/1 x 1/2 = 1/4 bald
1/2 x 1/2 x 1/1 = 1/4
F
FF
1/2 ♀
1/1 bald
1/2 long , 1/2 short
index
index
fingers
fingers
1/2 x 1/1 x 1/2 = 1/4
F
F
FF
Sex-Limited (Autosomes)
H - hen feathered
h - cock feathered - sex-limited to the male
P
Hen feathered x
hen feathered
HH
x
hh
H
h
F1
Hen feathered x Hen feathered
Hh
Hh
1/2 H 1/2 h
1/2 H 1/2 h
F2 Genotypes
Phenotypes
__________
__________
Hen feathered Hen feathered
Hen feathered Hen feathered
Cock feathered Hen feathered
1/4 HH
2/4 Hh
1/4 hh
F2 genotypic ratio - 1:2:1
F2 phenotypic ratio - - 3:1 - hen feathered:cock feathered
- 1 - hen feathered
.
156
CockFeathering
• Pointed
Feathers
HenFeathering
• Rounded
Feathers
Barred Plymouth Rock
CockFeathered
• Pointed
Feathers
• hh genotype
and male sex
• Cock feathering
is a sex-limited
trait!
• (limited to
males)
Hen-Feathered
• Rounded
Feathers
• hh genotype
and female sex
• Or any sex with
a H allele in the
genotype
Sebright
Chickens
Hen-Feathered
• Rounded Feathers
• This is a rooster
• He just has a
genotype with a
Hen feathered
allele, H
• Possible
genotypes: HH, Hh
Hen-feathered males
are desired in
Sebright Chickens
Hen-Feathered
• Rounded
Feathers
• Females can be
any genotype
(HH, Hh, or hh)
and will still be
Hen-feathered
• Cock-feathering
is a sex limited
trait-limited to
males
SEX-LINKAGE
Morgan (1910): Established the sex-linked inheritance of white eyes
in Drosophila melanogaster.
Example: P white male x red female, F1, F2, and reciprocal.
Criteria for identifying sex-linked recessive genes from pedigrees in
humans:
1. Occurs more often in males than females.
2. Gene is transmitted from an affected male through his
daughters to 1/2 of his grandsons.
3. Never transmitted from father to son.
4. An affected female had to have an affected father and
an affected or carrier mother.
Sex-linked Cross (P generation)
P homogametic parent x heterogametic parent
homozygous x hemizygous
AA x aY
or aa x AY
Genotypes are contrasting
F1 homogametic sex is heterozygous: Aa
F1 heterogametic sex is hemizygous: AY or aY
F2 is produced by crossing
+
F1s.
159
170
Reciprocal crosses - Drosophila
Sex-linked
1. P
F1
red
XWY
white
XwY
x
x
x
x
white
X wXw
red
XWXw
2. P
F1
white
x red
XwY x XWXW
red x red
XWY x XWXw
Autosomal
P
F1
normal
VV
normal
Vv
x
x
x
x
vestigial
vv
normal
Vv
P
F1
vestigial
vv
normal
Vv
x
x
x
x
normal
VV
normal
Vv
If the genes are on autosomes, reciprocal crosses in the P generation
will give similar results (F1 and F2).
If the genes are on x chromosomes (sex-linked), reciprocal crosses in
the P generation will not give similar results (F1 and F2).
160
1. Sex-Linkage in Drosophila melanogaster
Male = XY; Female = XX
W = red eye color (dominant); w = white eye color (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
Female
P
(ph) red
x
white
(ge) XWY
x
XwXw
(ga)
x
___
F1
(ph)
x
___
(ge)
x
___
(ga) ___
x
___
F2
F2
F2
Males
Females
Phenotype Genotype Phenotype Genotype
_________ _________ __________ _________
_________ _________ __________ __________
Genotypic ratio _____________________________
Phenotypic ratio (sex and eye color)_____________
(eye color) ___________________
(sex) ________________________
.
162
1. Sex-Linkage in Drosophila melanogaster
Male = XY; Female = XX
W = red eye color (dominant); w = white eye color (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
Female
P
(ph) red
x
white
(ge) XWY
x
XwXw
(ga) ½ XW ½ Y
x
1/1 Xw
F1
(ph) white
x
red
(ge) XwY
x
XWXw
(ga) ½ Xw ½ Y
x
½ XW ½ Xw
F2
F2
F2
Males
Females
Phenotype Genotype Phenotype Genotype
red
XWY
red
XWXw
white
XwY
white
XwXw
Genotypic ratio
1:1:1:1
Phenotypic ratio (sex and eye color)
1:1:1:1
(eye color)
1:1
(sex)
1:1
.
162
2. Sex-Linkage in Drosophila melanogaster
Male = XY; female = XX
W = red eye color (dominant); w = white eye color (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
Female
P
(ph) white
x
red
(ge) XwY
x
XWXW
(ga)
x
F1 (ph)
x
(ge)
x
(ga)
x
F2
Males
Females
Phenotype Genotype Phenotype Genotype
F2 Genotypic ratio __________________________
F2 Phenotypic ratio (sex and eye color) __________
(eye color) _________________
(sex) ______________________
.
163
2. Sex-Linkage in Drosophila melanogaster
Male = XY; female = XX
W = red eye color (dominant); w = white eye color (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
Female
P
(ph) white
x
red
(ge) XwY
x
XWXW
(ga) ½ Xw ½ Y
x
1/1 XW
F1 (ph) red
x
red
(ge) XWY
x
XWXw
(ga) ½ XW ½ Y
x
½ X W ½ Xw
F2
Males
Females
Phenotype Genotype Phenotype Genotype
red
XWY
red
XWXW
white
XwY
red
XWXw
F2 Genotypic ratio
1:1:1:1
F2 Phenotypic ratio (sex and eye color) 2:1:1
(eye color)
3:1
(sex)
1:1
.
163
F1
Parents
Male
Female
Male
Female
Progeny at 4 days
Male
Female
Progeny at 21 days
Female
Progeny at 6 weeks
Male
Progeny at 6 weeks
Progeny at 3 months
Male
Female
Sex-Linkage in Chickens
XY = female; XX = male
B = barred (dominant); b = nonbarred (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
P (ph) nonbarred
(ge) XbXb
(ga)
F1 (ph)
(ge)
(ga)
F2
x
x
x
x
x
x
Female
barred
XBY
Males
Phenotype Genotype
_________ ________
Females
Phenotype Genotype
_________ ________
_________ ________
_________ ________
F2 Genotypic ratio ________________________________
F2 Phenotypic ratio (sex and pattern) ________________
(pattern)
_______________
(sex) ________________
166
Sex-Linkage in Chickens
XY = female; XX = male
B = barred (dominant); b = nonbarred (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
P (ph) nonbarred
(ge) XbXb
(ga) 1/1 Xb
x
x
x
Female
barred
XBY
1/2 XB 1/2 Y
F1 (ph) barred
(ge) XBXb
(ga) 1/2 XB 1/2 Xb
x
x
x
nonbarred
XbY
1/2 Xb 1/2 Y
F2
Males
Phenotype Genotype
barred
XBXb
nonbarred
XbXb
Females
Phenotype Genotype
barred
XBY
nonbarred
XbY
F2 Genotypic ratio
F2 Phenotypic ratio (sex and pattern)
(pattern)
(sex)
1:1:1:1
1:1:1:1
1:1
1:1
166
Sex-Linkage in Chickens
XY = female; XX = male
B = barred (dominant); b = nonbarred (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
Male
P (ph) barred
(ge) XBXB
(ga)
F1 (ph)
(ge)
(ga)
F2
x
x
x
x
x
x
Female
nonbarred
XbY
Males
Phenotype Genotype
_________ ________
Females
Phenotype Genotype
_________ ________
_________ ________
_________ ________
F2 Genotypic ratio ________________________________
F2 Phenotypic ratio (sex and pattern) ________________
(pattern)
_______________
(sex) ________________
168
Sex-Linkage in Chickens
XY = female; XX = male
B = barred (dominant); b = nonbarred (recessive)
ph = phenotype; ge = genotype; ga = gametes; circle gametes
P (ph)
(ge)
(ga)
F1 (ph)
(ge)
(ga)
F2
Male
barred
XBXB
1/1 XB
barred
XBXb
1/2 XB 1/2 Xb
Males
Phenotype Genotype
barred
XBXb
barred
XBXB
Female
nonbarred
XbY
1/2 Xb 1/2 Y
barred
XBY
1/2 XB 1/2 Y
x
x
x
x
x
x
Females
Phenotype Genotype
barred
XBY
nonbarred XbY
F2 Genotypic ratio
F2 Phenotypic ratio (sex and pattern)
(pattern)
(sex)
1:1:1:1
2:1:1
3:1
1:1
168
1) A cock-feathered rooster is mated with a heterozygous hen-feathered hen. In a clutch of 4 eggs,
what is the probability of hatching 3 cock-feathered male and 1 hen-feathered female chicks (no
order specified)?
1/2
1/2+
1/2 cock-feather
1/2 hen-feather
1/1 hen-feather
hh x Hh
H h
h Hh hh
h Hh hh
P = 4! (1/4)3(1/2)1 = (4)(1/64)(1/2) = 4 = 1
3! 1!
128 32
2) A non-barred rooster is mated with a barred female. In a clutch of 4 eggs, what is the probability
of hatching 2 barred male and 2 nonbarred female chicks (no order specified)?
P = 4! (1/2)2(1/2)2
2! 2!
XB
y
Xb
Xb
XB Xb XB Xb
X by
X by
3) A woman heterozygous for long index finger length marries a man also with long index finger length.
What is the probability that they will have 1 daughter with long index fingers and 2 sons with long index
fingers (no order specified)?
long
short
+
FF′
F
F
1/2
1/2 long
1/2 short
FF
FF′
F′F′
x
F
FF
FF
+
long
short
FF
F′
FF′
FF′
1/2 +
1/1 long
P = 3!
(1/2)1(1/4)2
1! 2!
P = (3)(1/2)(1/16) = 3/32