Triploidy and other chromosomal abnormalities in a selected line of chickens

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Triploidy and other chromosomal abnormalities in a

selected line of chickens

Mh Thorne, Rk Collins, Bl Sheldon

To cite this version:

Triploidy

and other chromosomal

abnormalities in

a

selected line of chickens

MH

Thorne,

RK

Collins,

BL

Sheldon

CSIRO Division

_{of Animal Production, Poultry Genetics,}

PO Box

_184,

North

_Ryde,

NSW 211,!, Australia

(Proceedings

of the 9th

_{European Colloquium}

on

_Cytogenetics

of Domestic

Animals;

Toulouse-Auzeville,

10-13

_July

₁₉₉₀₎

triploid

/

chicken

_/

meiosis

_/

diploid ova

Triploidy

has been

reported

in the chicken in both

_embryos

and adults

_(de

Boer et

al,

1984).

Triploid

chick

_embryos

with ZWW sex chromosomes are not viable

_beyond

the first few

_days

of

_incubation,

but some with ZZW and ZZZ sex chromosomes survive to

_hatching

and

_maturity.

The ZZW

triploids

have an adult intersex

phenotype

and ZZZ

_triploids

a male

_phenotype.

Both are sterile

(Thorne

et

_al,

1988).

Intersex

_triploid

chickens have been detected each _year in our CSIRO

_Synthetic

layer

strains at low

_frequencies

_(0.1-0.5%).

Selection for

_triploidy

in one of the

Synthetic

lines has

_produced

a

_unique

line of chickens that have _up to

20%

triploid embryos

and

8-12%

hatched

_triploids

each

_generation.

The line also has a low

_frequency

of live

_{haploid-diploid}

and

_{diploid-triploid}

chickens

_(Thorne

et

_al,

1987).

Selection line females ovulate a

_high

incidence of

_diploid

ova from errors

at both meiosis I and II.

_Triploids

are then

_produced

after fertilization

_by

normal

haploid

spermatozoa. The

_tendency

to

_produce

_diploid

ova is

_genetically

determined

(Thorne

et

_al,

_1980).

This _paper

_presents

details of the incidence and sex ratio of

triploid embryos analyzed

in 4

_generations

of selection for

_triploidy

and the other

types

of chromosomal abnormalities observed in

_early

_embryos.

The

_{high triploid}

line was

_developed

from a

_Synthetic

_layer

selection strain that

_originated

from a White

Leghorn

x

_Australorp

crossbred flock

_(Thorne

et

al,

1987).

The first

_generation

of the line was formed

_by

_inbreeding

close relatives of intersex

_triploids

_(Thorne

et

_al,

_1980).

The second

_generation

was also

_produced

from inbred

_matings

but thereafter the line has been

_reproduced

at

_yearly

intervals

by

outbred

_matings

among selected parents. Females of

_generations

_{1, 3,}

4 and 5

were selected as breeders if

_{they produced}

one or more

_{triploid embryos}

out of 20

embryos karyotyped

at 3

_days

of incubation.

To

_{karyotype embryos,}

_eggs were incubated for 72

_h,

then 0.1 ml of

0.1%

vinblastine sulfate

_(Lilly)

was

_injected

into the air cell. After 2 more hours of

2)

slow

embryos,

3)

dead

embryos

or

₄₎

membrane

development

only.

Embryonic

malformations were recorded if

_present.

Chromosome

preparations

were made

_using

the

technique

of Shoffner et al

_(1967).

On every

slide,

5 clear

metaphase

cells were counted and _{up to} 30

metaphases

if chromosome abnormalities were

_present.

Interphase

nucleoli were counted to confirm the

_ploidy

level. As the chicken has

only

one nucleolus per

haploid

chromosome set

(Auer

et

al,

1987),

diploid embryos

will have 1-2

_nucleoli,

_triploids

1-3

nucleoli,

etc.

Chromosome abnormalities were found in 390

embryos

out of a total 2 936

early

chick

embryos

analyzed

in 4

_generations

of selection for

_triploidy

_{(table I).}

_They

included 207

_triploids

and another 28

presumptive

triploids,

each with 1-3

nucleoli,

but unclear chromosomes. Three

triploids

had

_aneuploid

cell lines

₍₁

_3AZWW-2;

1

3AZZZ-2;

1

_3AZZW+3).

The

_remaining

155 abnormal

_embryos

included 47

_haploids

(all 1AZ),

1

_tetraploid

_(4AZZWW)

and 4

_pentaploids

_{(all 5AZZZWW).}

Another 34

_embryos

had abnormal nucleoli but unclear

_polyploid

chromosomes

_including

20

embryos

with 1-5

nucleoli,

9 with 1-4 nucleoli and 5 with 1-6 nucleoli.

Haploid

mosaics included 43

_{haploid-diploids}

_{(29 Z/ZZ,}

14

_Z/ZW),

4

haploid-diploid-triploids

(2

Z/ZZ/ZZW;

1

_Z/ZZ/ZZZ;

1

_Z/ZW/ZWW)

and 3

haploid-triploid-pentaploid

(Z/ZZW/ZZZWW)

and a

_{haploid-diploid-tetraploid}

_embryo

with

_{higher ploidies}

_{(Z/ZZ/ZZZZ/HP).}

Diploid-polyploid

mosaics included 5

_{diploid-triploids}

_{(4 ZZ/ZZZ;}

1

_ZW/ZWW),

6

diploid-tetraploids

(4 ZW/ZZWW;

2

_ZZ/ZZZZ),

2

_{diploid-tetraploid-octaploids}

(both ZW/ZZWW/8n)

and 2

_diploid-high

_ploidies.

Two other abnormalities

in-cluded a trisomic

_embryo

(2AZW+2)

and a

_{diploid embryo}

with a Robertsonian translocation

_involving

chromosomes 3 and 4.

Most of the abnormalities observed in our data have been

_reported

_by

others

(reviewed

in

_Fechheimer,

_1981).

The chicken appears to have errors of

_meiosis,

fer-tilization and

_{early cleavage}

that can

_produce

_complex

chromosomal abnormalities. In

_general,

the

_haploid

cells of

_haploid

mosaics are derived from mitotic divisions of

supernumerary

spermatozoa

(Fechheimer, 1981),

while the

_{diploid-polyploid}

mo-saics

_(eg,

_{2n/4n, 2n/4n/8n)}

are

thought

to result from failure

_{of cytokinesis}

in

_early

cleavage

divisions

_causing

_doubling

of some cells. The

diploid-triploid

_mosaics,

how-ever, have been

postulated

to arise from binucleated

_oocytes

with meiotic errors in one nucleus

_{(Fechheimer, 1981).}

The 3n and 5n cells of the

_ln/3n/5n

embryo

may

have been derived from a binucleate

_oocyte

with meiotic errors in both nuclei.

Triploids

may arise

androgenetically

from the union of a

_haploid

ovum with a

_diploid

_sperm or 2

_spermatozoa

_(dispermy),

or

_{gynogenetically}

from the union of a

_diploid

ovum with a

_haploid

_sperm.

_Diploid

_gametes

_may be

_{produced by}

chromosomal

non-disjunction

at meiosis I or II and also in females after

_suppression

of

_{polar body}

extrusion or

by

_re-entry

of a

polar body.

The ZWW

triploids

can

only

be derived from

_females,

while ZZW and ZZZ

_triploids

can arise from either maternal or

_paternal

errors. The sex ratio of

_triploid

_embryos

_{(table II)}

_supports

a

_{gynogenetic origin.}

The sex ratios of the 4

_generations

were not

_{significantly}

different

_(P

>

_0.5),

so the data were

pooled. They

show a ratio of ZWW:ZZW:ZZZ

triploids

which is not

_{significantly}

different

_(P

>

_0.1)

from the 1:2:1 ratio

_expected

after fertilization of

_WW,

ZW or ZZ

_diploid

ova if MI and MII failed with

_equal

frequency

in females. It _appears

_unikely

that _any of the ZZW or ZZZ

triploids

are

_androgenetic

in

_origin.

In

_mice,

the

_LT/Sv

strain

_produces

over

30%

_triploid

embryos

because females

_{spontaneously}

ovulate a

_high

incidence of

diploid

_primary

oocytes

(O’Neill

and

_Kaufman,

_1987).

Non-disjunction

at

_metaphase

of MI and MII is

_thought

to be a

_possible

cause

of

_diploid

ova in females. This is

_{supported by}

the observation that

_haploid

(lAZ)

and

_pentaploid

_(5AZZZWW)

_embryos

_(and

_{unkaryotyped embryos}

with

androgenetic resulting

from fertilization of a

_nulloid

_{polar body}

or ovum in which the chromosomes have been lost

_{by non-disjunction.}

The

_pentaploids

_may result from fertilization of a ZZWW

_tetraploid

ovum formed

_by

non-disjunction

at both 1VTI and 3/III.

The

_development

of

_{triploid embryos}

at 3

_days

of incubation

supports

the observation that ZWW is lethal

_{(table III).}

_Only

22%

were

alive,

but all of these

were retarded or malformed and were not

_expected

to survive. In

_comparison,

50%

or more of ZZW and ZZZ

_triploids

were

_normally

developed embryos.

Membranes

lacking

an

_embryo

accounted for almost

80%

of

_presumptive

triploids

_showing

1-3 nucleoli. Lack of mitoses in this tissue made

_karyotyping

difficult.

_Among

the malformations observed in

_{triploid embryos, microphthalmia}

was the most common. The response to selection for

triploidy

was

_rapid

_{(table IV).}

The

_proportion

of tested females

_producing

triploid embryos

was

82.0%

by

the S5

generation

and

the incidence of

_triploid

_embryos

reached

20.8%.

The

_genetic

basis of the

_tendency

for

_diploid

ova is

currently being

studied. The data

_suggest

that there may be a

genetically

mediated

_{susceptibility}

to

_{non-disjunction}

in selection line females which

is

_responsible

for the

_high

incidence of

_diploid

ova.

REFERENCES

Auer

_{H, Mayr B,}

Lambrou

_M,

_Schleger

W

₍₁₉₈₇₎

An extended chicken

_{karyotype, including}

the NOR chromosome.

_Cytogenet

Cell Genet

_45,

218-221

de Boer

_LEM,

de Groen

_TAG,

Frankenhuis

MT,

Zonneveld

AJ,

Sallevelt

_J,

Belterman RHR

₍₁₉₈₄₎

Triploidy

in Gallus domesticus

_embryos,

_hatchlings

and adult intersex

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O’Neill

GT,

Kaufman MH

₍₁₉₈₇₎

Ovulation and fertilization of

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and

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27-36

Shoffner

RN,

Krishan

_A,

Haiden

_GJ,

Bammi

R,

Otis J

₍₁₉₆₇₎

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Thorne

MH,

Sheldon

BL,

Bobr LW

₍₁₉₈₀₎

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_apparently

inherited

triploid

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_{Proceedings of}

the South

_Pacific

Poultry

Science

Convention, Auckland,

65-70

Thorne

MH,

Collins

RK,

Sheldon BL

₍₁₉₈₇₎

Live

_{haploid-diploid}

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_{(Gallus domesticus).}

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Cell

_{Genet 45,}

21-25