Genome size in Calomys laucha and Calomys musculinus (Rodentia, Cricetidae)

HAL Id: hal-00893985

https://hal.archives-ouvertes.fr/hal-00893985

Submitted on 1 Jan 1993

HAL is a multi-disciplinary open access

archive for the deposit and dissemination of

sci-entific research documents, whether they are

pub-lished or not. The documents may come from

teaching and research institutions in France or

abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est

destinée au dépôt et à la diffusion de documents

scientifiques de niveau recherche, publiés ou non,

émanant des établissements d’enseignement et de

recherche français ou étrangers, des laboratoires

publics ou privés.

Genome size in Calomys laucha and Calomys musculinus

(Rodentia, Cricetidae)

Ma Ciccioli, L Poggio

To cite this version:

Original

article

Genome

size in

_Calomys

laucha

and

_Calomys

musculinus

(Rodentia, Cricetidae)

MA

_Ciccioli,

L

_Poggio

Facultad de Ciencias Exactas _{y Naturales, DePartamento} de Ciencias Biol6gt*cas,

Centro de _{Investigaciones} Gen!ticas

_{(UNLP-CONICET-CIC),}

_{CC4, Llavallol,}

182l, Buenos Aires, Argentina

(Received

12 _{April 1991; accepted} 28 December

1992)

Summary - The DNA content of 2 related species, Calomys laucha Thomas

_(C

₁₎

_(2n

= _64,

fundamental number =

74)

and Calomys musculinus Fisher

(C m) (2n

= _38, fundamental

number =

62)

was studied using Feulgen microdensitometry using Mus domesticus as a

control. Amounts of

_(haploid)

DNA in the 2 _species were _{significantly} different

_(Cl:

6.940

pg; Cm: 6.202 pg; P <

0.05).

The results were _analyzed in relation to: the total _diploid

karyotype length measured from _{synaptonemal complexes} with a light microscope

(Cl:

735.55 pm; Cm: 446.30 !m; P <

_0.0001)

and from mitotic metaphase chromosomes

_(Cl:

222.074 pm; Cm: 102.651 pm; P <

_0.0001),

the metacentric-submetacentric autosome

number

_(Cl:

_8; Cm:

₂₂₎

and the area of chromocenters showing positive staining with

C-banding technique

(heterochromatin) (Cl: 100%;

Cm:

_99.66%).

The DNA amount in pg per unit length of karyotype

(measured

from synaptonemal

complexes)

is _higher in _Calomys musculinus

_(0.028

_pg/

_M

_m)

than in _Calomys laucha

(0.019 pg/t

t

m).

This indicates that there is not a constant amount of DNA associated with a _{given length} of _karyotype, which _suggests that the difference between the 2

species may involve differential packing of DNA. This could be due to: genic differences;

differential interactions between genes and the cellular environment;

and/or

alteration of gene expression following the formation of new _{linkage groups} due to chromosomal

rearrangements.

Calomys musculinus Calomys laucha C-value / karyotype length / synaptonemal complex

Résumé - Taille du _génome chez _Calomys laucha et Calomys musculinus _(Rongeurs,

Cricétidés). La teneur en ADN de 2 espèces apparentées Calomys laucha Thomas

(Cl

2n = _64, nombre _fondamental =

_7!!)

_{et Calomys} musculinus Fisher

(Cm

2n = _38, nombre

fondamental

= 62)

a été étudiée _par microdensitométrie avec Feulgen, en utilisant Mus

*

domesticus comme témoin. Les teneurs en ADN

(haploïde)

des 2 _espèces ont montré des différences significatives

(Cl

= _6,9l!0

pg; Cm = _{6,202 pg; P <}

0,05).

Les résultats

ont été _analysés en relation avec : la _longueur totale

(diploïde)

du caryotype, mesurée

en _{microscopie optique} à _partir des _{complexes synaptonémiques}

(Cl :

_{735,55 !m;} Cm :

l!l!6,30 ¡lm; P <

_{0, 0001)}

et à partir des chromosomes en métaphase

(Cl :

_{222,07 ¡lm;} Cm

: 102,65 _{pm j P} <

_0,0001),

le nombre des autosomes _{métacentriques-submétacentriques}

(Cl : 8,

Cm :

₂₂₎

et la _surface des chromocentres montrant une coloration _positive avec

la _technique de bande C

_{(hétérochromatine) (Cl :}

100%;

Cm :

_99,66%).

La _quantité d’ADN _exprimée en _{picogrammes par} unité de longueur du _caryotype

(mesurée

sur les _complexes

synaptonémiques)

est plus élevée chez Calomys musculinus

(0,028

pg/¡tm)

que chez Calomys laucha

(0,019

pg/p,m).

Cela indique et suggère que la

différence entre ces 2 espèces pourrait impliquer un _{empaquetage différent} de l’ADN. Cela

pourrait être dû à des _{différences géniques,} des interactions _{différentielles} entre les gènes

et le milieu cellulaire,

et/ou

des expressions de _{gènes modifiées} suite à la formation de

nouveaux _groupes de liaison _{par suite} de remaniements chromosomiques.

Calomys musculinus _{/ Calomys} laucha _/ valeur-C _/ longueur du caryotype / complexe synaptonémique

INTRODUCTION

The genus

Calomys

(Phyllotinae)

has not been

completely

studied and the

tax-onomical and

_{phylogenetical relationships}

between its

_species

are still somewhat

uncertain

_(Cabrera,

_{1961; Hershkovitz, 1962;}

_Reig,

_1984).

The ancestral

_karyotype

of the

_Phyllotinae

is 2n = 70, fundamental number

(NF)

=

_68,

_most of the

chromo-somes

_being

acrocentric

(Pearson

and Patton

1976).

The _present

species

of

Calomys

exhibit a _range of chromosome numbers from 2n = 64

(NF

=

68)

to 2n = 36

(NF

=

68) (Hurtado

de Catalfo and

Waimberg,

1974; Lisanti et

al,

1976; Pearson and

Patton,

1976; Gardenal et

_al,

_1977; Forcone et

_al,

_1980).

’

C laucha and C musculinus are 2 cricetid

rodents,

significant

from a health

point

of view because

_they

are vectors of the Junin virus which causes the

Argentine

haemorrhagic

fever

_(Gardenal

et

al,

1977).

These 2

_species

are

_synmorphic

and

sympatric species

(Hershkovitz,

1962; Massoia et

al,

1968; Gardenal et

_{al, 1977;}

Reig,

1984)

and it is very difficult to differentiate them in the field.

_However,

_they

present very distinctive

karyotypes

since C laucha has 2n = 64

(NF

=

74)

and

C musculinus has 2n = 38

(NF

=

62)

chromosomes

(Pearson

and

Patton,

1976;

Gardenal et

al, 1977;

Ciccioli,

1988,

1991).

The main mechanism involved in the chromosomal evolution of rodents is that

of Robertsonian fusions

_(White,

1973;

Capanna

et

al, 1976;

Gropp

and

_Winking,

1981). Although

this mechanism would be the most

_{parsimonious explanation}

in

Calomys

(Pearson

and Patton

_1976),

other _types of _{rearrangements} are needed

to

_explain

the

_karyotype

_change

between the 2

_species,

such as

superimposed

pericentric

inversions

_(Forcone

et

al, 1980; Ciccioli,

1991).

In C musculinus a double

centromeric

region

was observed

by

electron

microscopy

(EM)

on

synaptonemal

complexes

(SC) (Ciccioli, 1991)

in ca 12 of a total of 19 bivalents

(Ciccioli

and

Rahn, 1984; Ciccioli,

in

_{preparation).}

Moens

₍₁₉₇₈₎

observed in

_{Neopodismopsis}

double in size and structure&dquo;. In house

_mice,

Redi et al

₍₁₉₈₆₎

said that &dquo;it has been inferred

_(Gropp

and

_Winking,

₁₉₈₁₎

that Rb translocation occurs with loss of

the 2 shortest arms of the acrocentrics involved in

_{translocation, probably}

followed

by

functional inactivation of a centromere

_(Hsu

et

_al,

_1975)&dquo;.

This mechanism does

not

_{necessarily imply}

a

_quantitative

variation in total DNA content since in Mus

poschiavinus

there is

_apparently

little or no

_quantitative

change

in genome size

(C-value) (Manfredi-Romanini

et

_{al, 1971;}

_Comings

and

_{Avelino, 1972;}

Redi et

al,

1986).

The difference in genome size between C laucha and C musculinus are studied

by

Feulgen

microdensitometry

in the _{present paper.} The aim of this work is

focused on the

_{relationships}

between DNA content and the total

_karyotype

_length

(TKL) (measured

on

synaptonemal complexes

(SC)

and on

_metaphase

mitotic

chromosomes

_(MMC)),

as well as other

nucleotypical

_parameters

(Bennett,

1987;

Grant,

1987).

Moreover,

additional information on _genome size will be discussed.

MATERIALS AND METHODS

Six male individuals from

_{Laguna Larga}

_(Province

of

C6rdoba,

Argentina)

of

each

_species

_(C

laucha and C

_musculinus)

and one individual of Mus domesticus

(Province

of Buenos

_Aires)

were studied.

DNA content measurements

_{(Feulgen microdensitometry)}

Slides were

prepared by

dispersion

and

air-drying

from

_specimens

which had not

been

_pretreated.

In C

musculinus,

slides of meiosis

_{(from testis)}

and mitosis

_(from

bone

_marrow)

were made. In C laucha and M

_{domesticus ,}

the same

_procedure

was

followed

_using

_only

bone marrow.

Hydrolysis

was carried out with 5 N HCl at 20°C. Different times of

_hydrolysis

were tested

(10,

_{20, 30,}

_35,

_40, 50 and 60

min)

and

hydrolysis

curves were

determined. After

_hydrolysis,

the slides were rinsed 3 times with distilled water

for 10 min each.

Staining

was carried out with

_Feulgen

stain at

_pH

2.2 for 2 h. Slides were rinsed

3 times in

S0

2

-water

for 10 min each

_time,

and then in distilled water

_{(10 min).}

The slides were air-dried in the dark and mounted in

_Euparal.

In slides of _testes, measurements were made on

spermatids

and _sperm, and

lymphocytes

were measured in slides of bone marrow. The values obtained were

expressed

in

_arbitrary

units

_(AU),

or in absolute units

_(pg

of

_DNA)

_using

Mus

domesticus as a

control,

the DNA content of which is known

_by

chemical methods

(C

= 7 pg

(Lewin,

1980)).

To ensure the accuracy of the measurements in the case of C

musculinus,

the

relationships

between DNA content measurements at

_prophase

_(4C)

and

_telophase

(2C)

was checked to

_correspond

to the ratio 2:1 in

mitotic

_lymphocytes

_(AU

35.23 and AU 16.85

_{respectively)}

and 4:1 in

_prophase

I

_(4C)

and

_telophase

II

_(1C)

of meiotic cells

_(AU

_36.24; AU

_9.63).

The amount of

_Feulgen

_staining

per nucleus was measured at a

_wavelength

of 570 nm

_using

the

_scanning

method in a Zeiss

_Cytoscan.

In both

_species,

the

measured. The differences in DNA content between

_species

were tested with a

Student t-test.

Synaptonemal

complexes

using light microscopy

(L1V1)

Synaptonemal

complexes

(SC)

were studied

_using

the method described

_by

Solari

(1983)

for electron

_microscopy,

_adapted

_by

_modifying

the stain to 50%

_(W/V)

of

AgN0

3

in distilled water. Two or 3

_drops

of silver nitrate solution were

placed

on

previously

air-dried slides.

_{Floating coverslips}

were put on the

slides,

which were

incubated in a moist chamber at 60°C for 3-5h.

_Staining

was monitored under a

phase

contrast

_objective

until

_{yellowish pachytene}

nuclei were seen with dark brown

SCs. The process was

_{stopped by washing}

with distilled water. Slides were air-dried

and mounted in DEPEX.

The total

_{karyotype length}

_(TKL)

was measured from

_{optical micro-photographs.}

Five

_{mid-pachytene}

nuclei were measured for each

_species.

The

_length

of the SC was measured 3 times and an _{average value} was determined for each autosomic

bivalent. The same

_procedure

was followed for the lateral elements of the X and

Y chromosomes. The TKL

_(SC)

was’calculated

_{by doubling}

the average value for

each autosome and

_adding

that of the lateral elements of the sexual

_pair.

All

mea-surements were carried out

_using

a

_Mini-Mop

_(Kontron)

_Image

_Analyzer.

The dif-ferences in TKL

_length

measured on SC

(LhI)

between

_species

were tested with a

Student t-test.

Conventional

_karyotypes

The animals were

_injected

with a _yeast solution on 2 successive

_days

to increase the mitotic index

_(Lee

and

_Elder,

_1980).

On the third

_{day they}

were

_injected

with a colchicine solution

(0.0025%).

Two hours _later,

_they

were etherized and

the bone marrow extracted

_according

to routine

_techniques

_(Evans

et

_al,

_1964).

The

_preparations

were made

_{by dispersion}

and

_air-drying.

The

_karyotypes

were described

_according

to the nomenclature

_{proposed by}

Levan

et al

_{(19G4) (m,}

sm and st: chromosomes with centromeres in the

median,

sttbmedian and subterminal

_region,

_{respectively).}

The _{average centromeric}

_indexes,

short

arms,

long

arms, total chromosome

length

and chromatid width were measured

and calculated in 3 cells. The total chromosome volume

_(TCV)

was

obtained

by

considering

each chromosome as 2

_cylinders.

The formula used was

(II

x

r

2

x

_h)

x 2

_(r

= half the chromatid

width;

h = chromosome

length).

Measurements _were carried

out

_using

a

_Mini-Mop

(Kontron)

_Image

Analyzer.

The differences in TKL

_length

on

mitotic

_metaphase

chromosomes between

_species

were tested with an

_approximate

Student t-test

_(Games

and

Howell,

1976),

on the

_assumption

of

_{heterogeneity}

of

variances

_(Sokal

and

_Rohlf,

_1981).

C-banding

The

_{C-banding technique}

was

performed

on

conventionally prepared

slides as

follows:

_a)

60% acetic acid for 30 _min;

_b)

0.2 N HCl for 1

_h;

_c)

solution

_(OH)

₂

e)

2% Giemsa in buffer

_{phosphate ph}

6.8 for 10-12 min. The heterochromatin

area _per

_interphase

nucleus was obtained

_{by measuring}

the area of each C _positive

chromocenter within each nucleus. The total area of chromocenters from 10 nuclei was

averaged

in each

_species.

The values obtained are

expressed

in table I where

C laucha is

_given

the 100% value. The measurements were carried out

_using

a

Wini-Mop

(Kontron)

Image Analyzer, working

with

_{photomicrographs}

with similar

exposure

time, development

procedure

and

enlargement

in both

species.

RESULTS AND DISCUSSION

The

_karyotype

of C laucha

_(2n

=

_64;

NF =

74)

comprised

8 m-sm

(pairs 1-4)

+ 54

st-t + X

_(m)

Y

_{(m) (fig 1A).}

C musculinus

_(2n

=

38;

NF =

62)

had _a

karyotype

with 22 m-sm

(pairs

1 to

₁₁₎

+ 14 st +

X(m)

Y

_(m)

_{(fig 1B).}

The

_species

were measured at their

_optimum

hydrolysis

time,

ie: C laucha:

lym-phocytes

30 _min; C musculinus:

spermatids

35 _{min, sperm} 40 min and

_lymphocytes

between

_spermatids

and

_sperm

in C musculinus

_{(arbitrary units)}

are remarkable

and _may be

_{explained by}

the

_{higher degree}

of chromatin condensation in _sperm. This could be due to the chromatin condensation

_gradient

which could have

hydrolysis

(Holmquist, 1979).

This could also

_explain

the small differences found in

the

_optimum

_hydrolysis

time between both

_species.

Table I shows the DNA content

_expressed

in absolute values

_(pg)

in both _species. The differences in C-values between C musculinus and C laucha were

_significant:

t

(46)

= 2.331,

P =

0.0226) (Bartlett

_test for

homogeneity

of variances,

X

Z

=

1.8877,

DF

_{= 1,}

P =

0.1656).

The DNA content and TKL

presented

_a

positive

relationship

with chromosome number

_(table

_I).

Synaptonemal complexes

in

_{mid-pachytene}

nuclei of C laucha and C musculinus

prepared

for the

_light

_microscope

_(L1!I)

are shown in

figure

3. The difference in the

total

_karyotype

_length

_(TKL)

between C laucha and C

_musculinus,

as measured

from

_SCs,

was

highly significant:

t(8)

=

7.88,

P = 0.000076

(Bartlett

test for

homogeneity

of variances

_X

₂

=

_1.3288,

DF = _1, P =

0.2475) (table I).

Comparisons

of TKL based on SC measurement can be

_inaccurate,

because of

at least 2

_possible

sources of error

(Anderson

et

al,

1985).

One is the

_biological

variability

among different

substages

of

pachytene.

This variation must be discarded

in the present

study

because

_only

nuclei in

_{mid-pachytene}

were chosen. The other is

the

_{physical stretching}

of SCs

_{during dispersion}

in the

_{hypotonic hypophase.}

In the

present

work,

those nuclei which showed evidence of

_stretching

were discarded. Still

another source of error, when different

species

are

_compared,

involves the

_quantity

of heterochromatin.

_Compared

to

_euchromatin,

heterochromatin

_is,

on _average, 2

to 5 times

_{under-represented}

in the

_length

of

_pachytene

_chromosomes,

due to its

different condensation state in

_pachytene

and

_metaphase

_{(Stack 1984).}

In both

_species

of

_{Calomys C-banding}

revealed that the amount of

100%;

Calomys

musculinus =

99.66%) (table

I).

Thus,

the effect of differences in

the

_quantity

of heterochromatin on SC

_length

between the

_species

is

_negligible.

The heterochromatin was

expressed

in absolute value and not in relation to the nuclear

area of

lymphocytes

since both

_species

differ

significantly

in this _parameter

_(Cl

=

100%,

Cm =

54.43%).

This difference follows the _same

pattern of variation as the

TKL. Such differences in TKL measured on mitotic

_metaphase

chromosomes are

larger

than those found on SCs

_(table

_I).

Differences in the TKL between C lauch,a a

and C musculinus measured on mitotic

_metaphase

chromosomes was

_highly

signif-icant:

_t’(5)

= _37.27, DF = 4.72 .:; _5, P = 0.00002

(Bartlett

test for

_{heterogeneity}

of variances

_X

₂

=

4.2227,

DF =

1,

P =

0.0375).

The _use of mitotic

_arresting

_agents

such as colchicine _may also lead to errors because

they produce

dose-related

vari-ation in chromatin contraction. In the _present

_{work, however,}

this should not be an

_important

source of error since the same dose concentration and exposure were

used

_during

the _experiments.

Variations in TKL for both sets of data

_{(SC, MMC)}

show the same _pattern of

variation which suggests that the

_{highly significant}

differences between the

_species

are not an artefact but have a

high

_genetic

_component.

Anderson et al

₍₁₉₈₅₎

showed that there is a _strong correlation between TKL

(SC length)

and genome size in

_{higher plants, indicating}

that a constant amount

of DNA is associated with a

_given

_length

of

_SC,

at least when

_averaged

over the

whole genome. Whereas this statement is

_convincing

when

_species

within the same

genus are

_compared

_{(eg Allium)}

_indicating

that

_they

have a similar chromosomal

organization,

the range in variation in DNA content _{per unit} of SC

_length

is much

larger

when other _genera are included

_(eg

Solanum

_sparsi

_P

_ilum).

C laucha and

C musculinus also _present a

_positive

relationships

between DNA content and SC

length.

However, in _spite of

_{being closely}

related

_species,

the TKL of C musculinus

is 39.3%

_(SC)

and 54.3%

_(l!Il!IC)

lower than that of C

laucha,

while the difference

in DNA content is

_only

10.6%. It may be worth

mentioning

that the difference

of chromosome volume in mitotic chromosomes -

_though

not

_accurately

measured because chromosome width was near the resolution limit of our

_{Mini-Mop Image}

Analyzer -

is of the same order

(6.5%,

Cl = 318

;

3

p,m

Cm = ₂₉₇

¡tm

3

)

_as the

difference in DNA content.

Consequently,

the amount of DNA _per unit

_length

of

_karyotype

is much

_higher

in C musculinus than in C laucha

_{(Table I),}

and in these

_species

a

_given

length

of

karyotype

does not contain a constant amount of DNA. This _may be

_{explained by}

the existence of different interactions between the

_{nucleotypical}

_parameters such as SC

length

and DNA amount. This could indicate that differential

_packing

of DNA is an

_important

difference between the

_species,

due _{to, among} other reasons:

a)

genetic differences,

b)

differential interaction between _genes and the cellular

environment,

and/or c)

alteration of gene

expression

due to the formation of new

linkage

groups

following

chromosome _{rearrangements.} The TKL variation _pattern is similar to that of the nuclear area

_{(table I).}

Cavalier-Smith

₍₁₉₈₃₎

states that &dquo;the nuclear volume is

_jointly

determined

_by:

₁₎

nuclear DNA content;

2)

the

_degree

of

folding

of the DNA and its pattern of attachment to the nuclear

_{envelope&dquo;.}

In the

present

work,

the main factor

_responsible

for the

_significant

differences in nuclear

area and TKL could be the

_degree

of

_folding

as

_{suggested by}

the differences found

nuclear

_{envelope, probably}

due to the decrease in telomere number in

_Calomys

musculinus. These interactions could be considered _part of the _genome

_ecology

of

the genus

(Bennett 1987).

ACKNOWLEDGMENTS

The authors are _especially indebted to PE Brandham

_(Jodrell

_{Laboratory, RBG, Kew,}

UK),

CA Naranjo for critically reading the manuscript and for their valuable suggestions,

to the laboratory of virology

(Depto

Quimica Biol6gica, FCE y Nat, UBA) for the

specimens of C musculinus, and to F Kravetz for the specimens of C laucha and Mus domesticus. _They also thank R Cabrini for the use of a microdensitometer _belonging to

the CNEA and the statistician B Gonzalez for a careful revision of tests and data. This work was _{supported by} a CONICET _grant.

REFERENCES

Anderson

_LK,

Stack

SM,

Fox

MH,

Chuanshan Z

₍₁₉₈₅₎

The

_relationship

between

genome size and

synaptonemal complex length

in

higher plants. Exp

Cell Res 156,

367-378

Bennett MD

₍₁₉₈₇₎

Variation in

_genomic

form in

_plants

and its

_ecological

implica-tions. New

_{Phytol 106}

_(suppl),

177-200 .

Cabrera A

₍₁₉₆₁₎

_Catilogo

de los mamiferos de America del Sur. Rev Mus

_Arg

Cien Nat Bernardino

_Rivadavia,

Cien

_{Zool 4(22),}

309-732

Capanna

E,

Gropp A, Winking

H,

Noack

_G,

Civitelli MV

₍₁₉₇₆₎

Robertsonian

metacentrics in mouse. Chromosoma _58, 341-353

Cavalier-Smith T

₍₁₉₈₃₎

Cell volume and genome size. In: Kew Chromosome

Conference

II

_(Brandham

_PE,

Bennett

_MD,

_eds)

_Royal

Bot

_{Gardens, Kew,}

London Ciccioli

MA,

Rahn I

₍₁₉₈₄₎

Estudios mei6ticos en

Calomys

musculinus

(Rodentia,

Cricetidae).

In: XV

_Congr

_Arg

Genet

Corrientes,

25, Soc

_Arg

Gen6tica

Corrientes,

Argentina

Ciccioli MA

₍₁₉₈₈₎

_Cytogenetic

studies in

_Calomys

musculinus

_(Rodentia,

Criceti-dae).

Cytologia

53,

7-17

Ciccioli MA

₍₁₉₉₁₎

_Classical,

C- and

_{Cd-banding karyotypes}

in mitotic and meiotic

chromosomes of

_Calomys

musculinus

_{(Rodentia, Cricetidae).}

_Caryologia

_44(2),

177-186

Comings

DE,

Avelino E

₍₁₉₇₂₎

DNA loss

_during

Robertsonian fusion studies of the tobacco mouse. Nature

(Lond)

New Biol 237, 199

Evans

E,

Breckon

G,

Ford C

₍₁₉₆₄₎

An

_air-drying

method for meiotic

preparations

from mammalian testes.

_Cytogenetics

_3, 289-294

Forcone

_AE,

Luna

_MV,

Kravetz

_FO,

Lisanti JA

₍₁₉₈₀₎

Bandas C _y G de

_Calomys

musculinus

_(Rodentia,

_Cricetidae).

Mendeliana _4, 57-65

Games

_PA,

Howell JF

₍₁₉₇₆₎

Pairwise

_multiple

comparisons

procedure

with

_unequal

Ns

_and/or

variances: a Montecarlo

_study.

J Educ Stat _1, 113-125

Grant WF

₍₁₉₈₇₎

Genome differentiation in

_{higher plants.}

In.:

_{Diffe.rentiation}

Patterns in

_Higher

Plants

_(Urbanska

_KM,

_ed)

Academic

Press,

New

York,

ch _1,

9-32

Gropp

A,

Winking

E

₍₁₉₈₁₎

Robertsonian translocation:

_cytology,

meiosis,

segrega-tion _patterns and consequences of

heterozygosity. Symp

Zool Soc Lond _47, 141-181

Hershkovitz P

₍₁₉₆₂₎

Evolution of

_neotropical

cricetine rodents

_(Muridae)

with

special

reference to the

_phyllotine

group. Fieldia!a:

Zool 46,

1-524

Holmquist

G

₍₁₉₇₉₎

The mechanism of

_{C-banding depurination}

and

_{;3-elimination.}

Chromosoraa

_72,

203-224

Hsu

_TC,

Pathak

_S,

Chen TR

₍₁₉₇₅₎

The

_possibility

of latent centromeres and a

proposed

nomenclature system for total chromosome and whole arm

translocations.

Cytogenet

Cell Genet

_15,

41-49

Hurtado de Catalfo

_G,

_Waimberg

R

₍₁₉₇₄₎

_Citogen6tica

de

_Calomys

callosus callosus

_{(Rengger 1830), (Rodentia Cricetidae).}

Anllisi fi

m6trico del

_cariotipo

somatico.

_Physis

C 33

₍₈₇₎

215-219

Lee

MR,

Elder F

₍₁₉₈₀₎

Yeast stimulation of bone marrow mitosis for

_cytogenetics

investigations.

Cytogenet

Cell Genet _26, 36-40

Levan

A,

Fredga

K,

Sandberg

AA

₍₁₉₆₄₎

Nomenclature of centromeric

_position

on

chromosomes. Hereditas _52, 201-220

Lewin B

₍₁₉₈₀₎

Gene

Expression

2.

_Eukaryotic

Chromosorn,es. John

_Wiley

and Sons

Inc,

New

York,

1160

Lisanti

_JA,

Kravetz

FO,

Ramirez CL

₍₁₉₇₆₎

Los cromosomas de

_Calomys

co,lloszis

(Rengger) (Rodentia Cricetidae)

de la Provincia de Cordoba.

Physis C 35,

221-230

Manfredi-Romanini

_1!IGM,

Minazza

E,

Capanna

E

₍₁₉₇₁₎

DNA nuclear content in

lymphocytes

from Mus musculus

_L,

and Mus

_poschiavinus

_(Fatio).

Biol

Zool 38,

321-326

Massoia

_E,

Fornes

_A,

_Waimberg

_R,

Fronza T

₍₁₉₆₈₎

Nuevos _aportes al conocimiento de las

_especies

bonaerenses del

_{g6nero Calomys}

Rev Inv

_Agrop

INTA _5, 63-92 Moens PB

₍₁₉₇₈₎

Kinetochores of

_grasshoppers

with Robertsonian chromosome

fusions. Chromoso!n.a

_67,

41-54

Pearson.OP,

Patton JL

₍₁₉₇₆₎

_{Relationships}

among South American

phyllotine

rodents based on chromosome

_analysis.

J Mammal

_{57, 2,}

339-350

Redi

_{CA, Garagna}

_S,

Mazzini

_G,

_Winking

H

₍₁₉₈₆₎

Pericentromeric

heterochro-matin and A-T content

_during

Robertsonian fusion in the house mouse. Chromo-soma

94,

31-35

Reig

OA

_{(1984) Significado}

de los m6todos

_{citogen6ticos}

para la distinci6n e

interpretaci6n

de las _especies con

_especial

referencia a los mamiferos. In:

_Conf

_III,

Congr

Iberoam Zool IV.

_Peru,

Soc

_Zool,

Peru

Sokal

_RR,

Rohlf FJ

₍₁₉₈₁₎

_Biometry.

WH Freeman and

_Co,

New York

Solari AJ

₍₁₉₈₃₎

Recombination bars in human

_synaptonemal

_{complexes spread}

with sodium

dodecyl sulphate.

Microsc Elec y Biol

Cel7(1),

1-11 1

Stack SM

₍₁₉₈₄₎

_{Heterochromatin,}

the

_{synaptonemal complex}

and

crossing-over.

J Cell Sci _71, 159-176

White MJD

₍₁₉₇₃₎

Animal

_Cytology

and Evolution.

_Cambridge

Univ

_Press,