Genetics is a science concerned with structure and function of all genes in different organisms.

Gregor mendelFather of genetics

WHY SHOULD A STUDENT OF ORTHODONTICS BE INTERESTED IN

GENETICS????• Because they effect growth and

development and function of oral and facial structure which is important for an orthodontics.

• It also help us to diagnose ,treat and subsequently maybe prevent malocclusion from occurring in next generation.

• Genetic disorders in a general aspect can be considered to be of two types:-

Numerical disorder.Structural disorders.

• Numerical disorders:- These are those in which there is a change in the number of chromosomes within the cell.

• Eg:-– Polyploidy– Monosomy– Trisomy – Turner’s syndrome.– Klinefelter’s syndrome.

• Structural disorders:- Those in which there is change in basic composition & structure of chromosomes.

• Eg:-– Translocation.– Deletions. – Ring chromosomes.

MODE OF TRANSMISSION MODE OF TRANSMISSION OF MALOCCLUSION:-OF MALOCCLUSION:-

3. VARIABLE TRAITS :-• Occurrence of different but related type of

malocclusion within several generation of same family.

• Traits seen with variable expression eg,missing teeth,which are commonly seen feature in some families, but the same teeth may not be missing in different generations or within the same generation.

• A diagnosis of genetic malocclusion should be made on bases of longitudinal studies of padigree same family.

• Human potentialities are determined by the genotype, but their manifestation depends on environment.-also known as epigenetics

• Evidence of genes being responsible for a particular characteristic in the production of an anomaly can be masked by environmental conditions such as climate, economic condition ,oral hygiene.

• Knowledge of human inheritance is possible only from study of pedigree and not on experimentation.

• Humen twins can be of 2 types:-– Monozygotic twins.– Dizygotic twins.MONOZYGOTIC TWINS:- They

are two individuals developed from single fertilized ovum,which divides into two at an early stage of development.

These twins thus have a genetic make-up identical to each other.

• Dizygotic twins:- They are two individuals developed fromm two saperate ova,ovulated & fertilized by two different sperms.

• These twins are not genetically identical as they develop from two different embryos.

• AUTOSOMAL DOMINANT INHERITANCE• Trait appear in every generation .• An affected child must have at least one

affected parent.• About one half of the offspring of an affected

person are affected(reoccurrence risk is 50% at each conception)

• Both male & female persons are affected.

• Abnormal recessive genes are transmitted through hetrozygotes.

• Characteristics:• The trait visible only in siblings but not in their

parents and relatives .• Parents of an affected person may have been

blood relatives .• About one fourth of children are

affected;reccurrence risk is 25%.• Both male and female children have equal chance

of being affected.

• This type of inheritance is mostly X-linked • Predominantly males are affected • Heterozygous females are carriers expected to produce

normal & affected sons in ratio of 1:1 • An affected male never produces an affected son (for ex:

hemophilia)• Characteristic of x-linked recessive inheritance • males are affected more frequently than females• When the female parent is carrying the trait then 50% of

her sons are affected & 50% daughter are carriers• Affected male parent cannot transmit the trait directly to

his sons i.e. trait will skip a generation

• Affected male parent transmit the trait to his daughter but not to the son

• When affected females are homozygous they transmit the trait to all children irrespective of their sex

• When affected females are heterozygous – only 50% of children of both sexes have a chance of being affected

• The clinical features are due to cummulative effects of all polygenes as well as other factors

• Other factors may be certain other genes or local or general environmental factor

• Classical ex – cleft lip & cleft palate

• Developmental hereditary characteristics are influenced by local and general environmental factors and their penetrance and expressivity can be greatly modify by these influence

• Occlusal variations are polygenic that is control by many genes and various environmental factors

• Extreme deviation are due to chromosomal or single gene effect.

Genetics related to malocclusions

Class II :- The size ,position & relation of the jaws are to a large extend by genes.thus class II malocclusion exibiting skeletal anomalies such as prognathic maxilla or retrognathic mandible can be due to hereditary cause.

Class II div 1 malocclusion-Extensive cephalometric studies have been caried out to determined the heretibility of certain craniofacial parameter in class II div. 1 malocclusion.

• These investigation have shown that in the class II patient the mandible is significantly more retruded than in class I patients with the body of mandible smaller & overall mandibular length reduced.

• These studies also showed a higher correlation between the patient & his immediate family.

• Class II division 2 malocclusion:- this malocclusion is a distinct clinical entity & is a more consistent of definable morphometric features occuring simultaneously i.e. a syndrome than the other malocclusion types put forward by angle in early 1900s.

• These malocclusion comprises the unique combination of deep overbite,retroclined incisors,class II skeletal discripency.

• Class III :- true class III malocclusion underlying skeletal imbalance is usually inherited.

• These are said to have a strong genetics basis.

• Features include:– A retrognathic maxilla– Prognathic mandible or bothProbably the most famous eg.

Of genetic trait in humans passing through several generations is the pedgree of the so called Hapsburg jaw,

• Hapsburg family line that the mandibular prognathism was transmitted as an autosomal dominant trait. This could be regarded as an exception & in itself does not provide sufficient information to predict the mode of inheritance of mand. Prognathism.

1. Micrognathia2. Macrognathia.3. Cleft lip & palate.4. Gardners syndrome.5. marfan’s syndrome.6. Cherubism.7. Cleido-cranial dysplasia.8. Mandibulo-facial

dysplasia.9. Osteogenesis

imperfecta..

10.Downs syndrome.11.Bimaxillary protrusion.12.Bimaxillary atresia.13.Retarded eruption of

teeth.14.Hypodontia,

anodontia,oligodontia,etc

15.Abnormal overjet & overbite.

16.Openbite.17.High arched palate.18.Abnormal number &

arrangement of teeth