Methods in behavioral genetics
Категория: БиологияБиология

Methods in behavioral genetics. Pedigree Method: the history and the practical facets

1. Methods in behavioral genetics

Pedigree Method:
the history and the
practical facets


Genealogia (from Greek - γενεα + λογος) - a description of family history and
a building of a family tree.
It is a way to understand who we has descended from.
The purpose of making the pedigree may be different: either to find out all
the relatives or to raise the personal significance.
There is an ancient tradition of the remembering ancestors to ask them about
help and protection.
In later times pedigrees were a respectable proof of noble origination and had
being played a role in establishing of rights to the throne.
Genealogical Map Of The Plantagenette House


Nowadays, genealogy has become
more common, and many people
explore and maintain their lineage.
If in previous times the dynasty
founder was placed on the roots of
the tree nowadays the charts are
started from the upper position.
To complete a pedigree there is
necessary to use a maximal variety of
information sources:
- church and civil records about birth,
death, marriage, divorce, adoption;
- medical records;
- gravestones inscriptions, cemetery
records, and funeral home records


The history of connections between genealogical
trees and hereditary traits begins with the
name of Francis Galton (1822 – 1911).
Being Charles Darwin's half-cousin he also was a
multi-facetted person of Victorian age:
statistician, sociologist, tropical explorer,
geographer, anthropologist, meteorologist,
proto-geneticist, eugenicist, psychologist and
psychometrician, etc.
His name bonds with the first applications of
statistical methods to the study of human
differences and inheritance of intelligence, and
introduction in use of questionnaires and surveys
for collecting data.
He was a pioneer in eugenics, coining the term
itself and the phrase ‘nature versus nurture’.
His book Hereditary Genius (1869) was the
first social scientific attempt to study genius
and greatness.


A pedigree chart showing the inheritance of ability in the Wedgwood,
Darwin and Galton families (Eugenic Society, 1909)


Francis Galton: Intelligence & Eugenics


Genealogical symbols
1 – male
2 – female
3 – unknown sex
4 – married couple
5 – related couple
6 – siblingls or sibs
7 – identical twins
8 – non-identical twins
9 – miscarriage
10 – medical abortion
11 – born dead
12 –childless marriage
13 – carrier female
14 – dead kins
15 – proband
(a person whom from
the investigation has


Common type of pedigree
- All generations numbered with the Roman numerals
- The members of each generation are signed by the Arabic ones
- Signes of the people with visible traits are filled with solid or hatched colour
a – diabetes, b – neurofibromatosis, ! – personally observed


Round type of pedigree


Consider the pedigrees attentively and answer the
- What is the average frequency of the
(in each generation, over generation, once in few
- To a what sex the trait holders are belong?
(both sexes, female, male)
- What is the proportion of carriers of the trait
in the genus?
(more than half, less than half, singular cases)
- What children are born to carrier women?
(the ratio of possession of the trait and gender)
- What children are born to affected fathers?
(the ratio of possession of the trait and gender)



1. The symptom occurs in each generation of the
pedigree, which is called vertical disease transmission.
2. The ratio of sick and healthy persons approaches
3. In normal children of affected parents, all
offspring is healthy.
4. The ratio of affected boys and girls is equal.
5. Sick men and women equally transmit the disease to
their children - boys and girls.
6. The more severe the disease is reflected in
reproduction, the greater the proportion of sporadic
cases (new mutations).
7. Homozygotes can be born to two affected parents.
Their illness is usually more severe than that of



1. Parents are usually clinically healthy.
2. The more children in the family, the more than one
affected child are expected.
3. The less frequency of a mutant gene is in a
population, the more often the parents of the sick
child are close relatives.
4. If both spouses are sick, then all children will be
5. If one of spouses is sick but the other is healthy
unaffected children are born (if the last one is not
6. If a patient gets married a carrier of a mutant
allele, 50% of sick children are born, which imitates
the dominant type of inheritance).
7. Both sexes are affected equally.



1. Both men and women are affected, but the last
ones are 2 times more.
2. Sick women pass a pathological allele to 50% of
their sons and 50% of their daughters, on average .
3. A sick male transfers a pathological allele to all his
daughters, but not to his sons.
4. On average, women (because of heterozygosity)
suffer less than men, due to homologous chromosome
probably carries the normal allele .



1. Affected individuals are only boys.
2. About two-thirds of the cases descend from
mothers, and the other one-third due to new
mutations in a maternal X-chromosome.
3. Sick boys can have affected brothers and
maternal uncles.
4. New mutations are sporadic or singular cases.
5. Sisters of sick brothers have a 50% chance of
being carriers.
6. Carrier sisters pass on the gene to 50% of their
sons (affected) and 50% of daughters (carriers).
7. Healthy men do not transmit the disease.



1.The trait is inherited by only all boys.
2. If mutations are harmful to the formation of
testes or spermatogenesis, they are not inherited,
because the carriers are sterile.


Geschwind syndrome or Gastaut-Geschwind, is a group of behavioral
phenomena evident in some people with temporal lobe epilepsy.
Geschwind syndrome includes five primary changes: hypergraphia,
hyperreligiosity, circumstantiality, atypical sexuality (usually reduced), and
intensified mental life.
Individuals may demonstrate an intensified mental life, including deepened
cognitive and emotional responses. This tendency may pair with hypergraphia,
leading to prolific creative output and a tendency toward intense, solitary
Individuals that demonstrate hyper-circumstantiality (or viscosity) tend to
continue conversations for a long time and talk receptively
Some individuals may exhibit hyperreligiosity, characterized by increased
religious feelings, philosophical and spiritual interests
People with hypergraphia display extreme attention to details in their
writing. Some such patients keep diaries recording meticulous details about
their everyday lives. In certain cases, these writings demonstrate extreme
interest in religious topics. Also, these individuals tend to have poor
The novelist Fyodor Dostoyevsky showed symptoms of Geschwind
syndrome, including hypergraphia.



Revising of Mendel rules
General approaches to an estimation of heritability
Pedigree method
Twins method
Adopted children studies
Population studies
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