Mutations and major variants of skeleton in chicken Prepared by Pravin Budhathoki Department of Animal Breeding IAAS, TU, Nepal

1. MUTATIONS AND MAJOR VARIANTS OF SKELETON IN CHICKEN
PRESENTER
PRAVIN BUDHATHOKI
R-2020-ANB-06M
IAAS, TU

2. outline
1. Variation in appendicular skeleton
• Polydactyly
• Diplopodia
• Brachydactyly
• Ungual Osteodystrophy
• Creeper
• Wingless
• Micromelia
2. Variation in axial skeleton
• Rumplessness
• Abnormal or Missing maxillae
• Short upper beak
• Missing mandible

3. I. Variation in Appendicular skeleton
1. Polydactyly
• So called fifth toe
• Arises from the metatarsal of the first toe, or hallux, on the inner side of
the foot.
• Fifth toe normally consists of one metatarsal and two phalanges
• Action of a single dominant gene ‘Po’
• But its expression is extremely
irregular
Phalanges

4. No bird has more than
four toes except chickens of the Dorking,
Faverolle, Houden, Sultan, and Non-bearded
Silkie Bantams, all of which have five toes.
In these breeds the extra toe arises above the
base of the hallux and projects upward, never
touching the ground.

5. 2. Diplopodia
Partial doubling of structures in the foot
Consists of six toes per leg being grouped in two
complements of three toes each
Three toes of one complement are in the position of
digits II, III and IV of the normal foot.
The other complement, located on the medial side of
the normal tarsometatarsus, represents the
supernumerary group.
Normal digits are as usual
Supernumerary digits are generally smaller and
highly variable in size and in structure.
Action of autosomal recessive lethal gene dp.

6. Cont…

7. 3. Brachydactyly
In normal fowls IV is about 10 percent longer than II or a little more,
but in brachydactylous ones IV is as short as II or shorter.
There is a strong correlation with foot feathering - ptilopody
Regulate by autosomal incomplete dominant gene ‘By’.

8. 4. Ungual Osteodystrophy
This abnormality which affects
only a small part of the skeleton
i.e. ungual phalanx
The claw of the middle toe is
absent, shortened, or distorted on
one or both feet.
In the extreme cases all digits are
abnormal.
The exact genetic basis is not
clear.

9. 5. Creeper
All the long bones of the limbs are shortened.
Tibia appears more affected.
Some birds have the toe permanently curled.
All the adult creeper fowls are heterozygotes.
‘Cp’ gene, produced the condition in
heterozygotes.
Homozygote-lethal
Distinguishing characteristics of some breeds:
Japanese Bantams, Germen creeper or kruper

10. 6. WINGLESS
Most of the affected embryos lack wings completely, but a few may
show various degrees of development between rudimentary humeri
and normal wings.
All the abnormalities result from homozygosity for an autosomal
recessive gene ‘wg’
7. Micromelia
The limbs of the affected embryos are small
The femur, tibia and tarso-metatarsus are less than half of the normal
length but much thicker.

11. For some breeds rumplessness is distinguish characters such as:
 Rumpless Game, Araucana
A single dominant gene, Rp, is responsible for hereditary rumplessness.
ii. Variation in axial skeleton
1. rumplessness

12. Normal tail Accidental
Rumplessness
Complete genetic
rumplessness
Synsacral vertebrae
fused with the
synsacrum or pelvis
16 0 0
Free caudals 5 0 0
Pygostyle 1 0 0
Synsacral vertebrae 5 3 or 4 (Last one or
two vertebrae is lack)
3 or 4 ( Centre one or
two vertebrae is
missing)
Uropygial gland/oil
gland
1 0 0
Rectrices or tail
feathers
14 or 16 0 0
Small bony knob Present( on the end of
the last vertebrae)
Absent Present

14. 2. Abnormal or Missing maxillae
The character is recessive homozygous, and heterozygotes are normal.
In homozygous embryos the maxillae in the upper beak are either
absent or much reduced.
Premaxillae are normal in many cases but smaller than usual in some
embryos.
Nasal are present
The upper beak is frequently bent to one side
In some cases the eyes appear to be slightly smaller than normal.
Single recessive gene ‘mx’ in homozygous condition was responsible
for the abnormality.

16. 3. Short upper beak
The upper beak is shortened by amounts varying from about a millimeter up
to half its normal length.
Lower beak is apparently unaffected
Embryos thus affected are homozygous for an autosomal, recessive gene ‘su’.
4. Missing mandible
The mandible or lower beak, is reduced to vestige
The upper beak is also reduced but remains from one-quarter to two-thirds of
normal size.
Its is frequently pointed upward or even curved over the front part of the
head.
Recessive autosomal gene ‘md’ is responsible for this mutation.

17. References
Poultry Genetics -Mutations2 (edelras.nl)
Genetics of the Fowl: The Classic Guide to Chicken Genetics and
Poultry Breeding - F. B. Hutt - Google Books
Further studies on diplopodia | SpringerLink
Association of SNP rs80659072 in the ZRS with polydactyly in Beijing
You chickens (plos.org)
DIPLOPODIA: A LETHAL FORM OF POLYDACTYLY IN
CHICKENS | Journal of Heredity | Oxford Academic (oup.com)

18. Thank You