Heredogram: What is it? Chromosomes, Population Genetics, Symbology and Generated Information

The human body comprises about 50 trillion to 100 trillion cells.

These cells form the basic units of life and combine to create more complex tissues and organs.

Genes form a blueprint for protein production within each cell that determines how the cell will function.

Genes also determine physical characteristics or traits. The complete set of about 20,000 to 25,000 genes is called the genome.

Most cells have a similar basic structure. An outer layer, called the cell membrane, contains a cytoplasm fluid.

Within the cytoplasm are many specialized “little organs” called organelles. The most important is the nucleus, which controls the cell and houses genetic material in chromosome structures.


Chromosomes carry hereditary genetic information in long strands of DNA called genes.


Humans have 22 autosomal chromosomes and a single pair of sex chromosomes: XX in women and XY in men. Each chromosome pair includes one inherited from the father and one from the mother.

For most of the human genome, we receive half of our genes from our father and a half from our mother.

Each half represents a random combination of DNA passed down to our ancestors.

This recombination process makes it difficult to study the lines of descent because it creates a genetic mix of everyone that has come before.

Fortunately for anthropological geneticists, parts of the genome are passed on continuously from parent to child.

In these segments, the genetic code varies only through occasional mutations – random misspellings in the long sequence of letters that make up our DNA.

Population’s genetics


Random “copy errors” along the long orthographic sequence of base pairs of a genome are called mutations.

Mutations are random changes in an individual’s DNA sequence, which rarely occur in each new generation.

During reproduction, the DNA double helix of each cell separates into two unique strands. Individual threads are duplicated for the next generation, but the process is not always perfect.

Genetic diversity

As genetic markers are inherited, they are passed down from generation to generation, forming a complex history that can be traced back in time.


In the Y chromosome DNA, it is passed from father to son, and mitochondrial DNA is passed from mother to daughter.

Genetic information can be traced through time to an individual’s ancestors, and the ancestor can be identified by performing a herdogram.

It is also called genealogy, pedigree, or genealogical tree and can be used to determine the occurrence of a pattern of transmission of a characteristic.

Divergent branches of the genealogical tree, or hologram, can be traced to the “nodes” in the tree, where a unit divides in two directions (Father, mother) and so on.

Herdograms are diagrams that describe the biological relationships within a family and represent the transmission mechanism of the characteristics of the genome.

In other words, diagrams represent kinship relationships where each individual is represented by a symbol.

Through herdograms, it is easier to identify the types of genetic inheritance and the chances of a person having a hereditary characteristic or disease.

The purpose of a hologram is to have an easy-to-read graph that shows a particular characteristic or the presence of a genetic disorder in an individual.

It can be used for characteristics like having loose earlobes or genetic disorders like color blindness, Huntington’s disease, and other genetic factors.

Symbology of a hologram

The herdogram is a representation, made using an agreed symbology, of the kinship relationships between individuals.

We can develop a hologram from some pretty simple rules and knowledge of the system of representation of individuals.

To assemble a hologram, specific symbols represent the family genealogy. That is the kinship relationships and the characteristics present in the family.

Symbology includes using a square for males, a circle for females, and a rhombus for individuals of the anonymous sex.

The filled symbol represents the individual who exhibits the characteristic, while the empty symbol represents the individual who does not have the characteristics.

A diagonal line over the symbol (empty or filled) represents that the individual has passed away.

A line joining a pair of individuals represents the marriage between unrelated individuals. In contrast, the use of two lines indicates that the marriage is consanguineous (between related individuals, that is, between any relative).

A dotted line represents an extra-conjugal (extramarital) relationship, and a diagonal line on the marriage line represents divorce.

Children generated from weddings (any relationship) are represented by a line derived from the marriage line.

Specific representations for twins, miscarriages, and prenatal death are present in the symbology.

Identical twins highlighted in red rectangles in the figure above are of particular interest to genetics, as it is an unusual situation, discordant monozygotic twins.

Despite sharing the same genetic material, the pair disagrees in one or more characteristics, which is generally linked to mutations in one of the team members.

The information generated by a herdogram

The first thing to notice on a herdogram is whether the inheritance is recessive or dominant.

It is necessary to observe if couples with the same characteristics have different children.

In this way, it is enough to perceive that the characteristics not present in a child are determined by recessive genes.

Basically, from a deeper interpretation, the genotype of all the representatives can be inferred, and the premises followed, from the moment in which it was identified what type of character is dominant or recessive if it is linked to sex and the probability that they appear—genetic characteristics in the next generations.