Genetics is the field of how traits and characteristics get passed from generation to generation. One of the key concepts in genetics is the mode of inheritance, which refers to the way in which genes are passed down from parents to their offspring. Understanding modes of inheritance and the concept of dominant and recessive gene inheritance and variation is important for predicting the likelihood of inherited diseases and conditions and making informed decisions about genetic testing and counseling. 

 

Dominant and Recessive Gene Inheritance and Variation

 

Dominant Gene Inheritance

 

Dominant inheritance is a type of inheritance where only one copy of a gene is needed to express a trait. This means that if one parent has the dominant allele and the other parent does not, there is a 50% chance that their child will inherit the dominant allele and express the trait. However, for many disorders, a dominant mutation may occur in de-novo. This means that it is not inherited, but has accrued as a new event in the embryo.

 

An example of dominant inheritance is Huntington's disease, tuberous sclerosis inhereditary cancer genes which are caused by a dominant gene mutation. If a person inherits the mutant allele from one parent, they will develop the disease.

 

Recognizing dominant inheritance patterns in family trees is important. Affected individuals may have at least one affected parent, and the trait is often seen in every generation. However, dominant inheritance can also skip generations, or the previous generation may be very mildly affected.

 

A Clinical geneticist can study the family tree by making a pedigree and trying to understand the inheritance dominant or de-novo. Recurrence risk in future generations can vary from 50% to negligible depending on whether it was inherited or de-novo.

 

Recessive Gene Inheritance and Recessive Gene Definition

 

Recessive inheritance is a type of inheritance where two copies of a gene are needed to express a trait. This means that if both parents carry one copy of the mutant allele, but do not express the trait themselves, their child has a 25% chance of inheriting two copies of the mutant allele and expressing the trait.

 

An example of recessive inheritance is thalassemia, spinal muscular atrophy, and cystic fibrosis. To develop the disease, an individual must inherit two copies of the mutant allele, one from each parent, to develop the disease.

 

It is important to diagnose and identify the genetic cause of childhood disorders so that genetic counseling and reproductive options may be discussed with the complex.

 

Co-dominance and Incomplete Dominance

 

Co-dominance and incomplete dominance are two types of inheritance patterns that do not fit neatly into the categories of dominant or recessive gene inheritance.

 

Co-dominance occurs when both alleles of a gene are expressed equally in a heterozygous individual. An example of co-dominance is blood type, where a person with AB blood type has both A and B antigens on their red blood cells.

 

Incomplete dominance occurs when neither allele is dominant and the heterozygous individual expresses a phenotype that is intermediate between the two homozygous phenotypes. An example of incomplete dominance is snapdragon flower color, where a homozygous red plant crossed with a homozygous white plant produces pink offspring.

 

Chromosomal Disorders

 

Some genetic disorders occur not due to genes that are present on chromosomes but due to the normal number or structure of chromosomes. Chromosome deletion and duplications are reported in many disorders such as poor growth, developmental delay, autism, obesity, congenital defects etc.

 

Mitochondrial Disorders

 

Mitochondrial are known as the powerhouse of the cell Mitochondrial disorders occur due to changes in Mitochondrial DNA or other genes that impact the functioning of Mitochondria. The mitochondrial disorder can be inherited as autosomal recessive or it passes only through the maternal lineage. A  Mitochondrial disorder can evolve virtually any system of the body and present at any age, therefore a high index of suspicion is necessary for diagnosis.

Variations in Modes of Inheritance

 

Variations in modes of inheritance can occur when the expression of a trait is influenced by multiple genes or environmental factors. An example of a variation in the mode of inheritance is the inheritance of height. While height is influenced by multiple genes, it is also influenced by environmental factors such as nutrition and physical activity.

 

Recognizing variations in modes of inheritance patterns in family trees can be difficult, but studying the distribution of the trait in the population can provide clues.

 

Conclusion

 

Recognizing and correctly diagnosing genetic conditions can be challenging, but understanding the underlying genetics can provide clues. By understanding modes of inheritance, we can better predict the likelihood of a trait being expressed in future generations and make informed decisions about genetic testing and counseling and parental diagnosis.