CONTACT

EVG, molekularna diagnostika
Taborska ulica 8
SI-2000 Maribor  
Slovenia



 + 386 (0)40 566 273
(Available from 8.00 till 16.00)

 info@eurovetgene.com

   EVG@facebook

For a better understanding of inheritance we prepared a short explanation of three most common different modes of inheritance. Before we explain different inheritace patterns we would also like to give some general overview of genetics.

 

Every organism has a genetic material, which is DNA. DNA is composed of 4 nucleotides – Adenine (A), Thymine (T), Cytosine (C) and Guanine (G). DNA encodes for different proteins, which are composed of twenty amino acids. Proteins are carriers of different functions within cells and tissues (from metabolism of sugars and energy to transfer of electric pulses along neurons, cell and tissue structural elements, muscle contraction, blood filtering, hairs, nails, etc.). Even though the same genes code for same protein that performs the same function it is not necessary that nucleic acid sequence of the gene (and subsequently amino acids) is completely the same. Such variants of certain gene that lie on the same genomic locus are called – alleles. There can be many different alleles (variants of the same gene) in a population of individuals. Every animal has a diploid genome meaning that they carry 2 sets of chromosomes. One set comes from mother the other comes from father. This means that each gene in a cell is represented by two copies. This allows organisms survival in case one allele is damaged (mutated). Moreover diploidity of organisms enables recombination (exchange) of genetic material between chromosomes that is a basis of sexual reproduction of living beings. Autosomal chromosomes are chromosomes where recombination (or rearrangement of genetic material between two chromosomes) occurs freely, while sex chromosomes are chromosomes that do not exhibit recombination that enables the distinction between two sexes. There are two copies of sex chromosomes since only small genetic differences are needed for specie to develop male or female pattern. Recessive inheritance means that defect in father and mother allele are needed for expression certain phenotype (properties that can be seen or measured). Dominant inheritance means that defect of only one allele (either fathers or mothers) are needed for expression of certain phenotype. Homozygosis means that individual carries two alleles that are completely identical (DNA sequence), while heterozygosis means that individual carries two alleles that are different (DNA sequence). Below you can find further explanation of three most common patterns of inheritance found in genetic diseases tested.

 

Autosomal recessive

Autosomal recessive means that a trait is carried on »non-sex« chromosome (autosome) and that a trait is expressed only when both alleles (inherited from mother and father) are damaged (contain detrimental mutation). There are three possible genetic combinations in population of such individuals: homozygotes that carry two normal alleles, homozygote that carry two mutated alleles and heterozygote that carry normal and mutated allele. Heterozygotes in this case are the carriers of mutation since they do not express the disease (unwanted trait). It is especially important to test such animals for mutations, since mutated alleles are »silently« (without seeing unwanted phenotype) carried through the population and therefore enable out breeding of such mutations from population.

 

Autosomal dominant

Autosomal dominant inheritance means that a trait is carried on »non-sex« chromosome (autosome) and that a trait is expressed when one of alleles (inherited either mother or father) is damaged (contains detrimental mutation). There are three possible genetic combinations in population of such individuals: normal homozygote (carrying two normal alleles), affected homozygote (carrying two mutated alleles), affected heterozygote (carrying normal and mutated allele), since only single mutated allele already causes a disease.  The importance for genetic testing of such animals is primarily in early diagnostics of the disease and identification of animals before they mate because most of diseases with autosomal dominant mode of inheritance have an onset later in animals life, when animal already was able to have offspring.

 

X-linked recessive

X-linked recessive inheritance means that the trait is carried on a sex chromosome and that a trait is expressed only when both alleles (inherited from mother and father) are damaged (contain detrimental mutation). The difference is that in this case males usually carry only single copy of gene, inherited from mother, since male sex chromosome Y does not contain full DNA sequence as female X chromosome does. The females on the other hand contain two X chromosomes (one from mother and the other from father that obtained his from his mother – sibling’s grandmother). There are three possible genetic combinations in population of females: homozygotes that carry two normal alleles, homozygote that carry two mutated alleles and heterozygote that carry normal and mutated allele. Heterozygotes in this case are the carriers of mutation since they do not express the disease (unwanted trait). However there are only two possible genotypic combinations in population of males, since they carry only one copy of a gene: normal homozygote and affected homozygote. It is especially important to test such animals for mutations, since mutated alleles are »silently« (without seeing unwanted phenotype) carried through the population and therefore enable out breeding of such mutations from population.