The Federal Agency of Health Protection and Social Development
The Stavropol State Medical Academy
Biology with Ecology Department
Mackarenko E.N.,
Boldyreva G.I.,
Parshintseva N.N.
METHODS OF HUMAN HEREDITY STUDY
Stavropol 2008
ФЕДЕРАЛЬНОЕ АГЕНСТВО ПО ЗДРАВООХРАНЕНИЮ И
СОЦИАЛЬНОМУ РАЗВИТИЮ МИНЕСТЕРСТВА
ЗДРАВООХРАНЕНИЯ РФ
Ставропольская государственная медицинская академия
Кафедра биологии с экологией
The Federal Agency of Health Protection and Social Development
The Stavropol State Medical Academy
Biology with Ecology Department
Э.Н. Макаренко, Г.И. Болдырева, Н.Н. Паршинцева
Mackarenko E.N., Boldyreva G.I., Parshintseva N.N.
МЕТОДЫ ИЗУЧЕНИЯ НАСЛЕДСТВЕННОСТИ
ЧЕЛОВЕКА
Учебное пособие для студентов англоязычного отделения
METHODS OF HUMAN HEREDITY STUDY
Methodological manual for the students of the English-speaking Medium
Ставрополь 2008
Stavropol 2008
УДК 576.312.32/.38 (07.07)
ББК 28.059
М 15
МЕТОДЫ ИЗУЧЕНИЯ НАСЛЕДСТВЕННОСТИ ЧЕЛОВЕКА.
Учебное пособие для студентов англоязычного отделения (на английском
языке). – Ставрополь: Изд-во СтГМА. – 2008. – 40 с.
Авторы: Макаренко Элина Николаевна, кандидат медицинских наук,
старший преподаватель кафедры биологии с экологией;
Болдырева Галина Ивановна, старший преподаватель кафедры биологии
с экологией;
Паршинцева Наталья Николаевна, старший преподаватель кафедры
иностранных языков с курсом латинского языка.
Учебное пособие включает в себя основные темы курсов «Хромосомы
человека» и «Медико-генетическое консультирование» для студентов
англоязычного отделения. Оно состоит из следующих разделов: Структура
хромосом, Классификация хромосом, Виды хроматина, Химическая
природа хромосом, Уровни укладки ДНП, Этапы медико-генетического
консультирования и Главные методы изучения наследственности человека.
Рецензенты: Ходжаян Анна Борисовна, доктор медицинских наук,
профессор, зав. кафедрой биологии с экологией СтГМА;
Знаменская Стояна Васильевна, кандидат педагогических наук, доцент
кафедры иностранных языков с курсом латинского языка СтГМА, декан
англоязычного отделения деканата иностранных студентов.
УДК 576.312.32/.38 (07.07)
ББК 28.059
М 15
Рекомендовано к изданию Цикловой методической комиссией
Ставропольской
государственной
медицинской
академии
по
англоязычному обучению иностранных студентов.
© Ставропольская государственная медицинская академия. 2008
УДК 576.312.32/.38 (07.07)
ББК 28.059
М 15
METHODS OF HUMAN HEREDITY STUDY. Methodological manual for
the students of the English-speaking Medium (on English). – Stavropol. –
Publisher: Stavropol State Medical Academy. – 2008. – 40 p.
Authors: Mackarenko E.N., Senior Lecturers Biology with Ecology of
Department;
Boldyreva G.I., Senior Lecturers Biology with Ecology of Department;
Parshintseva N.N., Teacher of Latin and Foreign Languages Department of
Stavropol State Medical Academy
Presented methodological manual includes the basic themes of courses
“Chromosomes of a man” and “Medico-genetical consultation” for the
students of the English-speaking Medium. It consists of following chapters:
Structure of chromosomes, Classification of chromosomes, Kinds of chromatin,
Chemical nature of chromosomes, Levels of packaging of DNP, Stages of
medico-genetical consultation and main methods of human heredity study.
Reviewers: Hodzhayan Anna Boriusoivna, Professor, Doctor of Medicine,
Head Biology with Ecology of Department of Stavropol State Medical
Academy,
Znamenskaya Stoyana Vasilievna, Dean of the English-speaking Medium.
УДК 576.312.32/.38 (07.07)
ББК 28.059
М 15
© Stavropol State Medical Academy. 2008
ВВЕДЕНИЕ
Методическое пособие по биологии на английском языке
предназначено для студентов первого курса англоязычного отделения. Оно
включает основные темы из разделов «Хромосомы человека» и «Медикогенетическое консультирование».
Целью методического пособия явилось в сжатой и доступной форме
изложить сущность основных методов генетики человека, таких как
цитогенетические, биохимические методы, амниоцентез, близнецовый
метод, дерматоглифика, генеалогический метод и популяционностатистический метод.
Известно, что хромосомы являются структурным компонентом ядра
клетки, ответственным за хранение наследственного материала и его
передачу последующим поколениям. Поэтому перед описанием
цитогенетических методов в методическое пособие включена глава
«Хромосомы человека». В ней рассказывается о структуре хромосом,
химической природе и видах хроматина, уровнях укладки ДНП,
приводится классификация анафазных хромосом. Даются понятия о
кариотипе, кариограмме, идеограмме, половом хроматине. Наглядно
демонстрируется отличие между женским и мужским кариотипом.
Рассматривается Денверская классификация хромосом человека (1960) и
Парижская номенклатура (1971).
Представленные разделы биологии имеют тесную связь с
практической медициной и являются теоретической базой для диагностики
и профилактики наследственных заболеваний в человеческой популяции.
INTRODUCTION
Methodological manual in biology in English is for the first year students of
English-speaking Medium. It includes the basic themes from chapters «
Chromosomes of a man» and « Medico-genetical consultation ».
The purpose of the methodical manual is to state the essence of the basic
methods of genetics of a man, such as cytogenetical methods, biochemical
methods, amniocentesis, twins method, dermatoglyphics, genealogic method
and a population-statistical method in the compressed and accessible form.
It is known, that chromosomes are a structural component of a nucleus of
the cell, responsible for storage of a hereditary material and its transfer to the
subsequent generations. Therefore, the chapter «Chromosomes of a man» is
included before the description of cytogenetical methods in the methodical
manual. It tells about structure of chromosomes, the chemical nature and kinds
of chromatins, levels of packaging of DNP, classification of anaphase
chromosomes. Concepts of karyotype, karyogram, ideogram, and sexual
chromatin are given. Difference between female's and male's karyotype is
evidently shown. Denver classification (1960) and the Paris nomenclature
(1971) of man chromosomes are considered.
The submitted sections of biology have close connection with practical
medicine. They are theoretical base for diagnostics and preventive maintenance
of hereditary diseases in a human population.
CHROMOSOMES
The chromosomes are the vehicles of heredity. They carry the genetic
material DNA and are responsible for transmission of hereditary characters
(traits) from one generation to the next generation.
There are two states of chromosomes. Chromosomes are visible only
during the cell division. When the nucleus enters into the kinetic state or state of
division, the chromatin (interphase chromosome) undergoes characteristic
condensation, producing chromosomes. These structures were called
chromosomes (chroma = colour) due to their affinity for basic dyes. The latter
take shape during the prophase of nuclear division.
The chromosomes disperse again into chromatin filaments at the end of
nuclear division (telophase). Chromatin appears as a highly dispersed
macronuclear reticular network suspended in the nucleoplasm. Chromatin
network appears only when the cell is in the energetic state.
Brief History
Chromosomes were discovered by Hofmeister in the cells of the plant
Tradescantia in 1849. In 1875 E.Strasburger discovered thread-like structures,
which appeared during cell division. However, the name chromosomes was
proposed by Waldeyer in 1888. Beneden and Boveri made the important
discovery that the number of chromosomes remained constant in the members of
a species.
Number of Chromosomes
The chromosomes occur in full complement (diploid number) in the
somatic cells. In germ cells (sperms and eggs) only half of that number or
haploid number occurs. While "n" normally signifies the gametic or haploid
chromosomes number, "2n" is the somatic or diploid chromosome number in
an individual.
A diploid nucleus has two chromosomes of each type. Two similar
chromosomes are known as homologous chromosomes.
The number of diploid chromosomes presented in some of the important
animals is shown below.
Name of the animal
No. of diploid chromosomes
. Plasmodium vivax (mosquito)
4
. Ascaris lumbricoides
24
. Musca domestica (house fly)
12
Name of the animal
No. of diploid chromosomes
. Drosophila melanogaster (fruit fly)
8
. Apis mellifera (Honey bee)
Male (males develop parthenogenetically)
Female
16
32
. Culex pipiens (mosquito)
6
. Rana tigrina (frog)
26
. Canis familiaris (dog)
78
. Felis domestica (cat)
38
. Equus caballus (horse)
64
. Sus scrofa (pig)
40
. Homo sapiens (man)
46
Karyotype
Karyotype is diploid chromosome number of cell, which includes
chromosome number, size, shape of individual chromosomes and other
attributes (for example, position of centromere). This term was coined by
Russian scientist G.A. Levitzky in 1924.
In all types of higher organisms (eukaryota), the well-organized nucleus
contains definite number of chromosomes of definite size and shape. The term
karyotype is given to the group of characteristics that identifies a particular
chromosome set. A group of plants or animals comprising a species is
characterised by a set of chromosomes, which have certain constant features.
Hence, karyotype is a specific sign for any species. But the karyotypes of
different groups are sometimes compared and similarities in karyotypes are
presumed to represent evolutionary relationship.
Karyotype is studied in mitotic metaphase, when chromosomes acquire a
short, stout, rod-like shape due to condensation and spirally coiling of
chromatin.
Then the individual chromosome completes – karyogram or ideogram – is
composed.
Karyogram – chromosomes of diploid set of an organism (chromosomes
of metaphase plates) are ordered in a series of decreasing size.
Ideogram – haploid chromosome number (may be diploid chromosome
number) of a man is arranged in certain order especially according groups, as it
is in Denver classification (1960).
Karyotype of a Man
In a man 46 chromosomes (diploid) are present. Out of them, 22 pairs are
autosomes and one pair – allosomes (sex chromosomes).
Autosomes are the non-sex determining chromosomes and are concerned
with somatic functions.
Allosomes are also known as sex chromosomes and participate in sex
determination. The sex chromosomes in a man are designated as X and Y. Two
allosomes occur in a diploid cell, but only one is present in germ cells.
Allosomes in a man and a woman are XY and XX respectively (Fig. 1).
A
Fig.1.
A – metaphase plate;
B – normal female karyotype;
C – normal male karyotype.
B
C
Shape and Classification of Chromosomes
During the interphase chromosomes are very loosely coiled and dispersed
into long filamentous structures, spreading through out the nucleus. These
structures are called chromatin.
Condensation of chromatin begins at the start of prophase.
At leptotene stage of meiotic prophase, chromosomes appear as beaded
structures, bead-like nodules being known as chromomeres. Size of
chromomeres and interchromomeric regions are not constant, so that every
leptotene has its own particular pattern. The DNA is though known to
concentrate in the chromomeres, but is believed to be present in the
interchromomeric regions also.
Condensation and spiralisation are completed in the metaphase. Due to
these processes, chromosomes acquire a short, stout, and rod-like shape. A close
observation of the metaphase chromosomes reveals that they are made of two
identical, spirally coiled filamentous structures known as chromatids. They are
produced as a result of the replication of chromonema during the interphase.
Hence, the chromatids are distinct structures and are held together at a
point called centromere. The latter appears as a slightly constricted region and
is known as the primary constriction. The chromosomal segments lying on
either side of the centromere, are known as chromosomal arms (long arm and
short arm). The centromere may occur anywhere on the chromosome, but its
position is fixed in a given chromosome. On the basis of the location of the
centromere, chromosomes are classified into the following types.
Classification of Anaphase Chromosomes (Fig.2).
1. Metacentric chromosome: the centromere is located near the middle of a
chromosome. Such chromosomes acquire V- shape during nuclear
division.
2. Sub-metacentric: the centromere occupies not the mid point, but some
distance away from it. As a result, unequal arms are produced and the
chromosomes acquire “L” or “J”- shape during cell division.
3. Acrocentric: the centromere is located near one end of a chromosome and
the chromosomes acquire rod-shaped ones.
4. Telocentric: the centromere is located at the end of a chromosome and
such chromosomes are rare. They are absent in normal karyotype of a
man.
С
Fig. 2.
A – telocentric chromosome;
B – acrocentric chromosome;
C – sub-metacentric chromosome;
D – metacentric chromosome
Besides centromere, which produces a primary constriction in
chromosomes, secondary constrictions can also be observed in some
chromosomes. Such a secondary constriction if presents in the distal region
of an arm would pinch off a small fragment called trabant or satellite
(Fig.3). The satellite remains attached to rest of the body by a thread of
chromatin. Secondary constrictions may be found in other regions also and
are constant in their position, so that these constrictions can be used as useful
markers. Secondary constrictions can be distinguished from primary
constriction or centromere, because chromosome bends or shows angular
deviation only at the position of centromere.
Fig. 3.
secondary constriction
satellite
primary
constriction
5. Chromosomes having a satellite are marker chromosomes and are called
SAT-chromosomes. The chromosome extremities or terminal regions on
either side are called telomeres. If a chromosome breaks, the broken ends
can fuse due to lack of telomeres. The chromosome, however, can not fuse
at the telomeric ends, suggesting that a telomere has a polarity which
prevents other segments from joining with it.
Structure of Chromosomes
Detailed study of chromosome morphology reveals a coiled filament
throughout the length of a chromosome. This filament is called chromonema
(Vejdovsky, 1912). The chromonemata form the gene-bearing portions of the
chromosomes. The chromonemata are embedded in the achromatic substance
known as matrix. Matrix is enclosed in a sheath or pellicle (Fig.4). Both matrix
and sheath are non-genetic materials and appear only at metaphase when the
nucleolus disappears. It is believed that nucleolar material and matrix are
interchangeable i.e., when matrix disappears, nucleolus appears and vice versa.
A
B
Fig. 4.
A – structure of a
chromosome;
B – a mitotic metaphase
chromosome
It would be necessary here to make a distinction between chromonema
and chromatid. While a chromatid is a half of chromosome, two chromatids
being connected at the centromere, the chromonemata is a structure, which is of
a sub-chromatid nature, and there can be more than one chromonema in a
chromatid.
Euchromatin and Heterochromatin
Chromonema exhibits two types of coiling – paranemic and plectonemic
coiling (Fig.5). The chromonema are coiled together in such a way that they can
easily by separated in the paranemic coiling. In the plectonemic coiling their
separation is very difficult.
Fig. 5.
A – paranemic chromonema coiling;
B - plectonemic chromonema coiling
When chromosomes are stained with stains like acetocarmine or feulgen
(basic fuchsin) at prophase, a linear differentiation into regions having dark stain
and those having light stain becomes conspicuous. In 1930’s and 1940’s, Emil
Heitz and other cytologists studied this aspect and darkly stained regions were
called heterochromatic and light regions were called euchromatic.
Heterochromatic regions are constituted into three structures namely
chromomeres, chromocentres and knobs.
Chromomeres are regular features of all prophase chromosomes, larger
enough to reveal them, but their number, size; distribution and arrangement are
specific for a particular species at a particular stage of development.
Chromocentres are heterochromatic regions of varying size, which occur
near the centromere in proximal regions of chromosome arms. At mid-prophase,
many chromocentres can be resolved into strings of chromomeres, which are
larger than chromomeres found in distal regions. In some dipterans salivary
glands, the chromocentres of different chromosomes fuse to form large
chromocentres. The relative distribution of chromocentres is sometimes
considered to be of considerable evolutionary value.
Knobs are spherical heterochromatin bodies, which may have a diameter
equal to the chromosome width but may reach a size having a diameter, which is
several times the width of the chromosome. Very distinct chromosome knobs
can be observed in maize at pachytene stage. Knobs are valuable chromosome
markers for distinguishing chromosomes of related species and races.
Constitutive and Facultative Heterochromatin
Certain regions of chromosomes, particularly those proximal to
centromeres are constant, and are called constitutive heterochromatic regions
serving as chromosome markers. There are other heterochromatic regions, called
facultative heterochromatin and represented by whole sex chromosomes, which
become heterochromatic only at certain stages. For instance, in female humans
one X-chromosome is inactivated or becomes heterochromatic only
facultatively.
It is also established that DNA in heterochromatic regions replicates at a
time different than the DNA in euchromatic regions, and that genes in
heterochromatic region are inactive. But the earlier belief that no genes are
found in heterochromatic regions is not correct because genes could be located
in heterochromatic regions. The genes in heterochromatic region perhaps
become active for a short period. Y-chromosome is another example of
heterochromatic chromosomes having inactive genes in several dioecious plants
and animals.
Hence, depending on its stainable property, chromatin is classified into
euchromatin and heterochromatin. Euchromatin takes up little stain and
appears pale in colour. But the heterochromatin is deeply stainable and appears
dark in colour. During the interphase of the cell cycle, dispersed chromatin
produces euchromatin and condensed or undispersed chromatin produces
heterochromatin. The centromere and secondary constriction are examples for
heterochromatin.
Chemical Composition
The major chemical components of chromosomes are DNA, RNA, histone
proteins and non-histone proteins. Calcium is also present in addition to these
constituents.
DNA. DNA is the most important of chemical components of chromatin,
since it plays the central role of controlling heredity. Quantitative measurements
of DNA have been made in a large number of cases, which are reviewed by
H.Rees and R.N.Jones in 1972. The most convenient measurement of DNA is
picogram (10 12 gm), which is equivalent to 31 cm of double helical DNA. It is
interesting to note that a human diploid cell has 174 cm (5- 6 picograms) of
DNA, so that all cells in a human being may have DNA equal to 2  5  1010
km (100gm), a length of which is equal to 100 times the distance from earth to
sun. In comparison of these enormous lengths, DNA of bacteria measures only
1.1 mm – 1.4 mm.
Besides nucleic acids (DNA and RNA), there are proteins, both histone and
non-histone types, associated with chromosomes. Both kinds of chromosomal
proteins are important for regulation of gene activity in eukaryotes.
Histones. There are five fractions of histones, which have been differently
designated according to the method of isolation. However, in 1975, histone
nomenclature has been standardised and new designations have been proposed.
These designations of different types of histones are the next: H 1 , H 2 B, H2A, H3,
H4 .
H 1 - histone is most easily removed and so is least tightly bound. This may
thus be concerned with holding together a chromosome fibre. H 3 and H 4 are
extremely conserved; having the same structures in different species and should
thus have a common structural role.
Histones, isolated from diverse materials showed considerable similarity. It
is also assumed that general similarities in histones have been conserved during
evolution. This feature alone suggested that these proteins should play a
structural role rather than regulatory role. However, some important chromatin
reconstitution experiments conducted in the recent years have established that
histones do play a regulatory role. This regulatory role of histones is more of a
general nature rather than specific and is exercised by repressing the activity of
genes.
Non-histones. They display more but still limited diversity. In variety of
organisms, number of non-histones can vary from 12 to little more than 20 (in a
human being may have approximately 100). Heterogeneity of these proteins
suggested that these proteins are not as conserved in evolution as histones.
These non-histone proteins differ even between different tissues of the same
organism suggesting that they regulate the activity of specific genes. Chromatin
reconstitution experiments described in 1973 by R.S.Gilmour and J.Paul,
established that specific non-histone proteins switch on specific genes. These
experiments have since been confirmed in a number of cases (Barrett et al.,
1974; Groner et l., 1975).
Nucleosome – Subunit of Chromatin
and Solenoid Model
In 1974, R.D. Kornberg and J.O. Thomas proposed an attractive model for
basic chromatin structure involving DNA and histones. They suggested that
DNA interacts with a tetramer (H32 – H42) and an oligomer (H2A – H2B)2 , so
that a tetramer involving two molecules each of the histones H3 and H4, is
associated with two molecules each of the histones H2A and H2B and with 200
base pairs of DNA. This makes a repeating unit (Fig.6).
One molecule of H1 is also associated with each repeating unit. They also
proposed that the tetramer makes the core of the unit and oligomers determine
the spacing thus giving a flexible structure. This model is supported from
biochemical and electron microscopy results.
P. Outdet et al (1975) proposed the term nucleosome for repeating units,
which were observed as beads on strings under electron microscope.
Fig. 6. Original proposal for nucleosome repeating units, with DNA wound on
a series of beads.
In order to accommodate the nucleosome model for DNA, F.H.C. Crick
and A. Klug (1975) proposed a kinky helix for DNA. In 1982, Prof. A.Klug was
awarded Nobel Prize in Chemistry for his work on the development of
crystallographic microscopy and his discoveries on the structure of nucleic acid
protein complexes. Prof. F.N.C. Crick was awarded Nobel Prize in medicine
much earlier along with, J.D. Watson and M.N.F. Wilkins, for their discovery of
double helical structure of DNA.
More details of nucleosome structure are now available, which are
described in a recent article published in Scientific American (Vol. 244, 2.
1981). It has been shown that a nucleosome core consists of a chain of DNA
having 146 base pairs (rather than 200 base pairs) making 1 3/4 turns and coiled
around an octamer consisting of two molecules each of H2A, H2B, H3 and H4.
Nucleosome
=
200 base pairs + 2 molecules each of
H2A, H2B, H3, H4
11 nm in diameter
146 base pairs of DNA
of nucleosome core
60 base pairs of linker–DNA
H2 B
Linker DNA ( 60 base pair)
H2A
core
H4
Core forms octamer
Linker
H
4
DNA
+ 146 base
H3
pairs of DNA
H2 B
H3
H2 A
Thus it makes a string (DNA chain) on beads rather than beads on string.
One molecule of H1 holds the two ends of DNA in a nucleosome and is thus not
an integral part of a nucleosome. The nucleosome core having 140 base pairs
(instead of 200) is an enzymatically reduced form of the nucleosome (Fig.7).
Fig.7.
Model of full
nucleosome (not the
core particle)
showing role of H1
histone, which is
attached at the entry
and exit of two turns
of 166 base pairs
long DNA.
core
The nucleosomes are once again coiled into what is called a solenoid, so
that a solenoid model proposed.
Packaging of Hereditary Material
There are three levels of DNP packaging.
Fig.8.
Solenoid model, with a helix having about six
nucleosomes per turn, where H1 molecules on
adjacent nucleosomes are in contact
Second level - condensation
First level - compactization
First level –
compactization
nucleosome fibre
second level –
condensation
solenoid fibre
thin, long and “beadson- -a-string” chromatin
is condensed
fibre
third level –
spiralization
supersolenoid fibre
coiling
super coiling
L = 7 time
L = 40 time
L = 104 time
d = 11 nm
d = 30 – 40 nm
d = 1400 nm
300 – 400 A
140.000 Ao
o
o
110 A
Is characteristic for :
☻heterochromatin of
☻euchromatin of
interphase chromocome interphase chromocome;
☻prophase chromocome
☻metaphase
chromocome
Third level of hereditary material packaging
The hypothetical scheme of highest levels
of DNP packing (chromatin) (Fig. of M. Molitvin).
1-4 — nucleomere loops of packing different density;
5 — a site of nucleomere loops, having nucleosome
character of the organization; 6— nucleomer fragment
in inter-chromomeric sites of DNP; 7, 8 — proteins of
structural matrix ( 7 — in chromomere region, 8 — in
inter-chromomeric region of DNP).
Special Types of Chromosomes
The preceding section in this chapter dealing with chromosomes in
eukaryotes was devoted to structure and function of chromosomes as observed
in mitotic or meiotic cells in plants and animals. In certain organisms there are
special tissues where these chromosomes take up a special structure. Lampbrush
chromosomes of the vertebrate oocyte and giant chromosomes of salivary gland
cells of dipterans are such special types of chromosomes. Due to special
significance of these chromosomes, a relatively detailed account of these two
types of chromosomes will be presented.
Lampbrush Chromosomes
As indicated earlier, chromosome structure at the same stage of cell
division remains constant in the different kinds of cells in the same organism.
Chromosomes of a special kind are, however, found in a variety of primary
oocyte nuclei both in vertebrates and in invertebrates. Special kind of
chromosomes known as lampbrush chromosomes are found during the
prolonged diplotene stage of first meiotic division and in spermatocyte nuclei of
Drosophila.
Structure of Lampbrush chromosomes:
1 – DNP fibrils;
2 – chromomeres (coiled fragments of DNP in
prophase of cell division);
3 – single chromomere with loop of DNP (loop is
uncoil region of transcribed DNP);
4 – inter-chromomeric fragment of DNP
These lampbrush chromosomes are characterized by a remarkable change
in structure. The change in structure includes an enormous increase in length.
These chromosomes may sometimes become even larger than polytene giant
salivary gland chromosomes. The largest chromosome having a length up to l
mm has been observed in urodele amphibian. The chromosomes seem to have a
chromomeric pattern with loops projecting in pairs from majority of
chromosomes. One to nine loops may arise from a single chromomere. The size
of loops varies from an average of 9.5 μ in frog to up to 200μ in newt. The
chromomeres are connected by inter-chromomeric fibres. These pairs of loops in
these chromosomes give them the characteristic lampbrush appearance.
Frequently these loops exhibit a thin axis (which probably consists of one DNA
double helix), from which fibres project which are covered with a loop matrix
consisting of RNA and protein.
Total view of Lampbrush chromosomes
(B) a single loop
(observed structure)
(C) a single loop
(observed structure)
The number of pairs of loops gradually increases in meiosis till it reaches
maximum in diplotene. As meiosis proceeds further, number of loops gradually
decreases and the loops ultimately disappear due to disintegration rather than
reabsorption back into the chromomere. H. Ris, however, had thought that the
loops were integral parts of chromonemata, which are extended in the form of
major coils.
It is also believed that the loops represent the modified chromosome
structures at the loci of active genes. It has been observed that, if the activity of
these genes is checked by actinomycin D, the loops will collapse.
Numerous small nucleoli are commonly formed from the lampbrush
chromosomes due to the rings detached from the loops at specific loci. The
significance of the formation of numerous nucleoli is not known.
Polytene Chromosomes
In salivary gland cells of dipteran species, giant chromosomes were
observed by E.G. Balbiani for the first time in 1881. The availability of these
chromosomes greatly helped the study of cytogenetics in fruit fly. These
chromosomes may reach a size up to 200 times (or more) the size of
corresponding chromosomes of meiosis or in nuclei of ordinary mitotic cells.
Another characteristic of these giant chromosomes is that they are somatically
paired. Consequently the number of these giant chromosomes in the salivary
gland cells always appears to be half of the normal somatic cells. The giant
chromosomes have a distinct pattern of transverse banding, which consists of
alternate chromatic and achromatic regions. These bands have greatly helped in
the mapping of the chromosomes in cytogenetic studies. The bands occasionally
form reversible “puffs”, known as “chromosome puffs” or “Balbiani rings”,
which are associated with differential gene activation.
Structure of polytene chromosome:
1 – DNP fibrils;
2 – dark band (chromatic regions);
3 – chromosome puffs (regions with high gene
activity;
4 – light band (achromatic regions).
The giant chromosomes represent a bundle of fibrils, which arise by
repeated cycles of endo-reduplication of single chromatids. Endo-reduplication
means that the chromatin replicates without cell division, as a result of which the
number of chromonemata keeps on increasing. This is why these chromosomes
are also popularly known as polytene chromosomes and the condition is
described as polyteny. The number of chromonemata (fibrils) per chromosome
may reach up to 2000 in extreme cases.
In dipterans, the preparation of a slide of these chromosomes is rather easy.
The larvae are taken at the third instar stage and the salivary glands are dissected
out and squashed in aceto-carmine. In such preparations, these chromosomes in
aggregate reach a length of as mush as 2000 μ in Drosophila melanogaster.
In D. melanogaster, the giant chromosomes are found in the form of five
long and one short strands radiating from a single more or less amorphous mass
known as chromocentre. One long strand corresponds to the X-chromosome and
the remaining four long strands are the arms of II and III chromosomes. The
short strand is the small dot-like IV chromosome. The centromeres of all these
chromosomes fuse to form the chromocentre. In the male flies the Ychromosome is also found fused within the chromocentre and is therefore not
seen as a separate strand.
Chromosomes of
Drosophila
melanogaster:
A,B – Salivary gland
chromosomes;
C – Mitotic
chromosomes
(A)
(B)
How this enormous increase in size of these chromosomes is brought about
in salivary glands is not known and various hypotheses are available to explain
this issue. It should however, be emphasized that these giant chromosomes
though, commonly found in salivary glands, have also been found in malpighian
tubules, fat bodies, ovarian nurse cells, gut epithelia and some other tissues.
GENETICS OF MAN
The genetics of a man (anthropogenetics) is an independent section of
genetics, which studies features of a heredity and variability of a man. A man is
specific object of anthropogenetical studying, as:
1) it is impossible to apply the basic method of genetics –
hybridologic method;
2)
3)
4)
5)
difficult karyotype – 46 chromosomes;
the big number of groups of linkage genes – 23 groups of linkage;
has a small number of offsprings in each generation;
there is a slow alternation of generations.
Medico – Genetical Consultation
Medico-genetical consultation (MGC) is a kind of medical aid rendered to
the population with the purpose of preventive maintenance of hereditary
diseases.
The purpose: ● to lower frequency of a hereditary pathology in human
populations;
● to reduce expression of clinical symptoms of hereditary
diseases.
Medico-genetical consultation is carried out in some stages, which are
submitted in the table
Stages MGC
I. Specification
diagnosis
of
The actions which are carried out at a stage
1. Studying of phenotypes;
2. Drawing up and research of family trees
(genealogic method)
3. Cytogenetics method
the
4. Biochemical methods
5. Amniocentesis
6. Electrographic methods (cardiographia,
encephalographia, myographia, etc.)
II. Calculation of risk degree
of a hereditary pathology
III.
Delivery
of
the
conclusion and recommendations
1. On the basis of genealogic method
2. On the basis of twins method
3. Use of population-statistical method at
monogenic autosome – recessive diseases
4. Use of tables of empirical risk at
polygenic-inherited diseases
The note:
up to 10 % - a low degree of risk of a
hereditary pathology;
10 % - 20 % - an average degree of risk;
over 20 % - a high degree of risk
Methods of Human Heredity Study
I.
Cytogenetics Methods include:
1.1.
1.2.
1.3.
Karyotyping without differential dyeing;
Karyotyping with differential dyeing;
Research Barr bodies.
1.1. Karyotyping without Differential Dyeing: it is carried out under the
following circuit:
1. Placing lymphocytes (kind of leukocytes) in a medium
containing phitohemagglutinin.
2. Cultivation of the cells (mitotic division of the cells).
3. Stopping mitosis at metaphase by introducing colchicines
into the medium. Marking micropreparation, obtaining
microphotos of metaphase plates (karyotype).
4. Composition the individual chromosome complete
(karyogram).
Fig. 1
Fig. 1. Karyogram of normal female organism
Hence, last step of karyotyping is drawing up karyogram or ideogram
according to Denver classifications.
Karyogram – is the ordered arrangement of chromosomes of a metaphase
plate (a graphic representation of karyotype).
Ideogram – is distribution of chromosomes on groups in view of specific
attributes, for example as in Denver classifications.
DENVER NOMENCLATURE OF CHROMOSOME
The size, the form of chromosomes and centromere index are put in
basis of Denver classification (1960).
Centromere
index
=
length of chromosome short arm
length of the whole chromosome
DENVER CLASSIFICATION, 1960
Group Number
of chromosomes
Morphology of chromosomes
Size,
μm
Types of
chromosomes
A
1-3
Large
11-8,3
Metacentric
chromosomes
B
4,5
Large
7,7
Submetacentric
chromosomes
6-12;
Middle
7,2-5,7
Submetacentric
chromosomes
Middle
4,2
Acrocentric
chromosomes
Small
3,6-3,2
Small
2,3-2,8
Submetacentric
Chromosomes
Metacentric
Chromosomes
C
Xchromosome
D
E
F
G
X -chromosome
13-15
16-18
19-20
21,22
Y -chromosome
Ychromoso
me
Small
2,3
Acrocentric
chromosomes
All chromosomes are distributed on groups. In Denver classifications are
allocated seven groups – A, B, C, D, E, F, G.
Lack of Denver classifications: it is difficult to determine a serial number
of a chromosome inside group according to Denver classifications.
1.2.
Karyotyping with Differential Dyeing: it is carried out with the
purpose of identification of each chromosome. To identify any chromosome
became possible due to the Paris nomenclature, 1971.
Chromosomal and interchromosomal sites are painted differently at
processing of chromosome by special dyes. The chromosome gets characteristic
« striped kind ». Alternation of light and dark disks is strictly specific to each
chromosome, due to what it is possible to define its serial number.
PARIS NOMENCLATURE, 1971
1.3.
Research Barr Bodies
In man the presence of a Y-chromosome in a fertilized egg causes it to
develop into a male and it is the absence of the Y-chromosome that causes it to
develop into a female.
In man there are 23 pairs of chromosomes of which 22 pairs are known as
autosomes and one pair sex chromosomes. In a male the complement is 22
pairs of autosomes and the sex chromosomes are X and Y, while in female the
complement is 22 pairs of autosomes and one pair of X chromosomes.
Autosomes do not have any role in sex determination. A smear of the
epithelial tissue from the cavity of man can be examined to know the sex
chromosome complement. The cells of a female bear a special structure known
as Barr body or (Murray body). Normal male buccal smear cells do not have a
Barr body. The female is termed as sex-chromatin positive and male – sexchromatin negative. One of the X chromosomes in the female is inactive and is
presumed to form the Barr body. A variant of the sex chromatin occurs in the
neutrophil white blood cells. Here a ‘drumstick’ consisting of a fine stainable
thread and a round stainable head, protrudes from a nuclear lobe in a small
percentage of female cells but is nearly absent in nearly all male cells.
II.
Biochemical Methods take place at diagnostics of molecular
diseases. With their help it is possible to determine the quantitative contents of
enzymes, initial and intermediate products of a metabolism.
As a rule, on the first stage the screening - test (qualitative reaction to
presence of metabolism products) precedes to biochemical research. Various
mediums of an organism (blood, urine, cerebral fluid, amniotic fluid, etc.) are
exposed to biochemical research.
III.
Amniocentesis is a research of amniotic fluid, what is spent at term
of 16-18 weeks pregnancy for exception of molecular and chromosomal diseases
at a embryon.
1st stage is an obtaining amniotic fluid with embryonic cells
2nd stage is a carrying out cytological or biochemical researches.
AMNIOCENTESIS
amniotic fluid sampled
Mother’s body wall
Wall of uterus
Placenta
Fetus (16 weeks)
centrifuged
fluid
fetal cells
Chromosomes
examined
Chemistry of fluid
and cells analyzed
Cell cultured
IY. Twins Method
During evolution, selection has strongly favored the birth of only one
human baby at a time. The energy available from the mother, for nourishing the
unborn child and for milk production and care after the child is born, is limited.
Babies borne singly tend to be larger, and healthier, with a better chance of
survival, than those with wombmates. However, multiple births result from a
small percentage of pregnancies (1%).
Nonidentical twins (2/3) also called fraternal twins or dizygotic (“twozygote”) twins, result when two eggs are ovulated at the same time and both are
fertilized and implant in the uterine wall. Because the resulting embryos come
from different eggs and different sperm, they are no more alike than any other
children of the same parents, except that they are the same age. Dizygotic twins
are genetically non identical and may be as well of the same sex as of the
Fig. 2
A
Fig. 2. A – identical twins;
1- general placenta;
2- own amnion
3- general smooth chorion
4- general decidua capsularis
5-decidua parietalis
B
B – nonidentical twins.
1- own placenta;
2- own amnion;
3- own smooth chorion
4- own decidua capsularis
different sex. Hence, likeness of traits may be explained by influence of external
environment at the dizygotic twins.
Identical twins (1/3) are produced when the mass of cells formed by cell
division of the zygote separates into two groups in the fits week after
fertilization. Each group of cells develops into a separate embryo. Because these
cells contain identical genes, the resulting embryos are genetically identical and
so must be of the same sex. Identical twins are also called monozygotic twins
because they originate from a single zygote. Thus, likeness of traits may be
explained by equal genotypes at the monozygotic twins.
Concordance is likeness of traits at both twins, marking in percent (%). If
the sign absent at one from them it is called discordance (%).
Twin method helps to study the influence of environmental factors and
heredity on the development of traits.
V.
Genealogical Method includes some stages:
1st stage – gathering of data on members of family of several generations;
2nd stage – drawing up of a family tree;
proband – the person for whom the family tree is under construction;
sibs – brothers and sisters of proband;
rd
3 stage – the analysis of a family tree and an establishment such as inheritance;
4th stage – definition of proband’s genotypes and close relatives;
5th stage – grows degrees of risk on a family tree.
Designations at drawing up of a family tree
Designations
Symbol
male organism
female organism
proband
carrier of trait
●
carrier of a gene
marriage
allied marriage
sibs
infantile death
I
II
repeated marriage
The analysis of a family tree occurs under the following circuit:
1) the parity of sexes is determined;
2) number of trait carriers in pedigree (analysis on horizontal);
3) quantity of individuals with signs on a vertical;
4) specific features of pedigree.
Autosomal - Dominant Type of Inheritance
Аа
аа
аа
аа
аа
аа
Аа
Аа
1)
2)
3)
4)
аа
Аа
аа
Аа
аа
Аа
Аа
Аа
аа
аа
аа
аа аа
Аа
Аа
Аа
аа
Аа
Аа
аа
Аа аа
the trait equally frequently meets both in men, and in women;
there are many sick organisms in horizontal;
patients are in each generation;
one of parents of the sick child is necessarily sick.
Autosomal - Recessive Type of Inheritance
АА
●
▪
Аа
.
.
1)
2)
3)
4)
5)
●
аа
●
●
Аа
Аа
аа
Аа
●
●
Аа
●
Аа
Аа
●
Аа
аа
the trait equally frequently meets both in men, and in women ;
the pathological heredity takes place on a horizontal ;
the pathological heredity is traced on a vertical through 1-2 generations;
the indication in a family tree on allied marriage;
phenotypically healthy parents are carriers of a pathological gene.
The Х-linked, Dominate Type of Inheritance
ХАХа
ХаХа
ХАХа ХаУ
ХАХа ХАУ ХАХа
ХАУ
ХаУ
ХаУ
ХАУ
ХаУ
ХаУ
ХаХа
ХАХа
ХаУ
ХАХа
ХаХа
ХаХа
ХаХа
ХаУ
1) the trait equally frequently meets both in men, and in women;
2) the pathological heredity is traced at the big number of individuals on a
horizontal;
3) ill organisms are in each generation;
4) one of parents of the ill child is sick necessarily;
5) only sick girls and health boys are born from the sick father.
Х-linked, Recessive Type of Inheritance
ХАХа
ХАУ
●
ХАХа
ХАУ
●
ХаУ
ХАХа
●
●
ХАХа
1)
2)
3)
4)
ХАУ
ХАХА
ХАУ
ХаУ
●
ХаУ
ХаУ
ХаХа
ХАХа
ХАУ
ХАУ
ХАУ
ХАХА
ХаУ
ХАХА
ХАХА
male organisms is ill more than female organisms;
on a horizontal half of boys are ill, half of girls are carriers in family;
the trait is traced through 1-2 generations on a vertical;
sick individuals are relatives of a male on the part of proband’s mother.
The У-linked Type of Inheritance
X УА
XX
XX
X УА
X УА
X УА
X УА
XX
XX
XX
XX
XY
XY
1) only boys are ill;
2) proband brothers are sick too;
3) the sick boy is born from the sick father, that is inherited the abnormal
trait from generation to generation on a man's line.
VI.
Dermatoglyphics. Thumbprints found on contracts over two thousand
years ago show that the Chinese have long used fingerprints for signature and
identification. But for the Western World, fingerprints were ‘discovered’ by Sir
Francis Galton, a cousin of Charles Darwin, in 1893. Since then, massive
research has proven that there is a direct correlation between fingerprints and a
person’s medical and behavioral profile.
Dermatoglyphics is the scientific term for the study of fingerprints and
related line and hand shape designations. The word “dermatoglyphics” comes
from two Greek words (derma = skin and glyphic = carve) and refers to the
friction ridge formations, which appear on the palms of the hands and soles of
the feet. Characteristically, hair does not grow from this area. The ridging
formations serve well to enhance contact, an area of multiple nerve endings
(dermal Papillae) and aids in the prevention of slippage. People of African
ancestry display reduced skin pigmentation in the designated locations. All
studies of the dermal ridge arrangements including genetics, anthropology are
classified under the term dermatoglyphics.
The ridge formations of the skin of an individual begin to appear during the
third and fourth month of fetal development. After death, decomposition of the
skin is last to occur in the area of the dermatoglyphic configurations. There have
been many instances in which the only identifiable part of a deceased person
was the friction ridge formations.
Dermal palmer and plantar ridges are highly useful in biological studies.
Their notably variable characteristics are not duplicated in other people, even in
monozygotic twins or even in the same person, from location to location.
Because dermal ridges are found on a number of animals, it will be interesting to
observe whether dermal patterns are replicated in cloning and if they vary, how
they vary. The details of these ridges are permanent. Yet while the individual
characteristics are variable, that diversity falls within pattern limits that permit
systematic classification.
Dermatoglyphics is subdivided on
a) Dactyloscopy
b) Palmeroscopy
c) Plantaroscopy
Dermatoglyphics studies a skin relief and skin pattern on fingers
(dactyloscopy), on palms (palmeroscopy) and soles (plantaroscopy).
The dactyloscopy gives special attention on papillary patterns of fingers.
They have specific features at each person. In criminalistics they are used for
identification of the person. Papillary patterns on fingers distinguish as
L
A
W
loops – L (LU – the loop opens aside ulna; LR – the loop opens aside radius)
arches – A
curls – W
L> W> A
60 % of 34 % of 6 % - on hands
A> W> L – on soles
Palmeroscopy studies dermal palmer relief. It includes palmer lines and
heights. Central palmer dimple settles down on a palm. It is surrounded with six
heights. The largest is thenar (at basis of I finger). On the contrary lays
hypothenar (at the basis of V finger). Four heights are between fingers.
Manual triradii are formed at the basis of II, III, IY, V fingers – a, b, c, d
accordingly.
Triradius – a point where three of different direction papillary lines are
converged.
Triradius
Main triradius t (the line on border of a brush and a forearm at the basis of
IV tarsus bones) settles down on staple folding.
Palmer angle atd is 48о – 57о in norm. At a hereditary pathology it can
increase or decrease accordingly.
a, b ,c, d, t and td triradii
atd
angle
locations
Some of the main lines allocate on palms of the healthy person. At
hereditary syndromes they can merge, forming transversal palmary folding.
Vll. Population - Statistical Method
The totality of alleles of all genes in a population is the gene pool of that
population. The total gene pool continues as a constant representation of a
population. Modest alteration of the allelic frequency does not bring, marked
changes immediately, but over period of time such changes produce marked
alterations in the characteristics of a population.
Hardy and Weinberg (1908) proposed that the frequencies of alleles and
even the ratios of genotypes tend to remain constant from one generation to the
next in sexually reproducing populations under certain conditions. These
conditions include:
1. A very large population;
2. No change in mutation rates;
3. Complete randomness in mating so that success is the same for all allelic
combinations;
4. No large – scale migrations into or out of the mating pool.
In such populations gene frequencies follow simple laws of probability.
If the allele A has a frequency of “p” in a population and allele ‘a’ has a
frequency of “q” and there are no other alleles for this gene, p + q = 1.
The probability that allele A occurs is also its frequency p. The probability
that ‘a’ will occur is q. Thus the probability of the occurrence of homozygous
dominants AA or its frequency in a population is p x p = p2.
The frequency of ‘aa’ homozygotes is q2.
Since there are two ways of forming heterozygotes Aa (i.e. A allele from
mother and ‘a’ from father or vice versa) the frequency of Aa in the population
is 2 pq.
The sum of all these frequencies is
P2 + 2pq + q2 = 1
or
2
(p+q) = 1 This is a binomial expression.
Example: in a population in Hardy – Weinberg equilibrium, for a gene
with only two alleles, if the gene frequency of allele A is 0.4, then we can
calculate
frequency of a = 1 – p = 1 – 0.4 = 0.6
.. The frequency of various genotypes is
AA = p2 = (0.4) (0.4)
= 0.16
Aa = 2pq = 2 (0.6) (0.4)
= 0.48
2
Aa = q = (0.6) (0.6)
= 0.36
2
2
P = 2pq = q = 0.16 = 0.48 = 0.36 = 1
The selection pressures on the population are expressed by the deviations
from the Hardy – Weinberg gene genotype frequencies.
B I B L I O G R A P H Y:
1.
2.
3.
4.
5.
A textbooik of cytology, genetics and evolution, ISBN 81-7133161-0, P.K. Gupta ( a textbook for university students0, published
by Rakesh Kumar Rastogi for Rastogi publications, Shivaji Rood,
Meerut- 250002.
Biology, fourth edition, Karen Arms, Pamela S.Camp, 1995,
Saunders college Publishing.
Intermediate First Year, Zoology : Authors (English Telugu
Versions): Smt. K.Srilatha Devi, Dr. L. Krishna Reddy, Revised
Edition: 2000.
Review Committee, Dr. K. Malla Reddy, Sri Y. Krishnanandam, Sri
B.V.Gopalacharyulu, Sri G.Rama Joga Rao, Teludu Akademi.
Биология/ А.А. Слюсарев, С.В.Жукова. – К.: Вища шк.
Головное изд-во, 1987. – 415 с.
C O N T E N T S:
CHAPTER I: CHROMOSOMES
Introduction………………………………………………………….4
Brief history………………………………………………………….5
Number of chromosomes…………………………………………….5
Notion about karyotype………………………………………………6
Karyotype of a man…………………………………………………..7
Classification of anaphase chromosomes…………………………….8
Structure of chromosome……………………………………………..9
Kinds of chromatin…………………………………………………..10
Chemical composition of chromosomes……………………………..11
Solenoid model………………………………………………………12
Packaging of hereditary material…………………………………….15
lampbrush chromosomes………………………………………….....17
polytene chromosomes……………………………………………....19
CHAPTER II: GENETICS OF MAN
Medico-genetical consultation………………………………………...21
Cytogenetics methods………………………………………………....22
 karyotyping without differential dyeing……………..……22
 karyotyping with differential dyeing……….………….….24
 research Barr bodies……………………………….……...26
Biochemical methods……………………………………….………...26
Amniocentesis…………………………………………….…………..27
Twins method………………………………………….……………...27
Genealogical method……………………………………………..…...29
Dermatoglyphics……………………………………………………...32
Population-statistical method…………………………………………35
* DENVER CLASSIFICATION, 1960……………………...…...23
* PARIS NOMENCLATURE, 1971……………...…………..….25
METHODS OF HUMAN HEREDITY STUDY
Methodological manual for the students
of the English-speaking Medium (On English).
МЕТОДЫ ИЗУЧЕНИЯ НАСЛЕДСТВЕННОСТИ ЧЕЛОВЕКА
Учебное пособие для студентов
англоязычного отделения (на английском языке).
Авторы: Макаренко Элина Николаевна, кандидат медицинских наук,
старший преподаватель кафедры биологии с экологией;
Болдырева Галина Ивановна, старший преподаватель кафедры биологии
с экологией;
Паршинцева Наталья Николаевна, старший преподаватель кафедры
иностранных языков с курсом латинского языка.
Authors: Mackarenko E.N., Senior Lecturers Biology with Ecology of
Department;
Boldyreva G.I., Senior Lecturers Biology with Ecology of Department;
Parshintseva N.N., Teacher of Latin and Foreign Languages Department of
Stavropol State Medical Academy