Based on Genetic

Pedigree analysis: Pedigree analysis is the study of a specific attribute that is passed down from generation to generation. It aids in interpreting the pattern of inheritance for a specific characteristic, as well as determining if the trait is dominant or recessive. Application of Pedigree Analysis: Determination of Mode of Inheritance Example: A trait appearing in every generation and affecting both sexes suggests autosomal dominant inheritance. Identification of Carriers Example: In Sickle Cell Anemia, individuals with genotype AS appear normal but can transmit the gene to offspring. Risk Prediction for Offspring Example: Two carrier parents (Aa × Aa) have a 25% chance of producing an affected child in an autosomal recessive disorder. Genetic Counseling Example: A woman with a family history of Hemophilia is advised on the probability of having affected sons. Diagnosis of Genetic Disorders Example: A pedigree showing mostly affected males and no father-to-son transmission suggests X-linked recessive disorders like Color Blindness. Tracing Inheritance of Traits Across Generations Example: Tracking a trait like widow’s peak or attached earlobes through three generations in a family. Study of Rare Genetic Diseases Example: Pedigree analysis helps track rare conditions like Huntington’s Disease within affected families. Detection of Consanguinity Effects Example: Increased occurrence of recessive disorders in children born from cousin marriages. Evaluation of Penetrance and Expressivity Example: In Polydactyly, some individuals express extra fingers strongly while others show mild expression. Pedigree symbol: The rows indicate generations of a family in the pedigree chart. The squares and circles represent males and females, respectively. The people in the same row are from the same generation. A horizontal bar between the square and the circle represents a marriage or mating. A consanguineous (marriages between relatives) mating or marriage is indicated by a double bar between the symbols. The symbol of a black diamond indicates that the sex is unspecified and affected. A vertical line suspended perpendicular to the horizontal bar or marriage bar indicates the offspring. Individuals who are homozygous and affected by the trait are shown as fully darkened symbols. Individuals who are heterozygous or carriers are indicated by half-shaded symbols. Wild type refers to a normal or natural genotype. Individuals that are normal or unaffected are represented by unshaded squares and circles. A black mark in the middle of the symbol represents the carrier of a sex-linked recessive gene. Types of pedigrees On the basis of mode of inheritance, pedigree analysis is classified into five types. That are listed below: Autosomal dominant X-linked dominant Autosomal recessive X-linked recessive Y-linked Autosomal dominant When a disease is produced by a dominant allele of a gene, everyone who carries that allele will develop disease symptoms. Only one allele is able to affect the individual here. As a result, every affected person must have a parent who is also affected. Autosomal dominant is characterised by a pedigree with affected individuals in each generation. If the affected parent is heterozygous, there is a possibility with no affected children in a family. Examples of autosomal dominant traits are brachydactyly, polydactyly and dimple in the cheek. Characteristic features of autosomal dominant inheritance Transmission of trait occurs from parents to either sex. Males and females can be equally affected. The pedigree is vertical, which means that the trait is marked as present in all generations. Typically, multiple generations are affected. Autosomal recessive Autosomal recessive diseases require at least one copy of the disease allele in both parents of an affected individual. Most of the individuals having autosomal recessive traits are carriers. Autosomal recessive trait is distinguished from autosomal dominant and X-linked dominant in a way that affected offsprings have unaffected parents. These traits can skip a generation. The common example of this type of trait is albinism. Salient features of autosomal recessive inheritance Multiple male and female siblings, whose parents are normal but carriers, had an equal number of cases. The siblings are homozygous for the defective allele, but their parents are clearly heterozygous, that means they are only carriers of the trait, even if some of them appear normal. Consanguinity occasionally results in the appearance of such traits. X-linked dominant In X-linked dominant inheritance, the disease-causing gene is found on the X-chromosome, and the diseasecausing allele is dominant over the normal allele in females. Females have twice as many X-chromosomes as males, hence they are more likely to be influenced in the population than males. The X-linked dominant disorders are inherited by males from their mothers because they inherit their X chromosome from mothers. Example of this disorder is oral facial digital syndrome. Characteristic features of X-linked dominant inheritance The trait can be found in almost every generation, and it is passed down vertically. If the mother is affected, approximately half of her sons are also adversely affected. All of the male's daughters will be affected if he is affected, but none of his sons will be affected. There is no male to male transmission of disease in this inheritance. X-linked recessive Due to the fact that males only have one X-chromosome, any male who inherits an X-linked recessive disease allele will be affected. Therefore, in this type of inheritance, males tend to be affected more frequently as compared to females in a population. This type of inheritance can be seen in red green colour blindness and haemophilia. Salient features of X-linked recessive inheritance Females only show the trait if they are homozygous for the mutant allele. Men show it even if they are hemizygous. The males are most affected by this trait. Half of the sons of carrier females are affected. If the female is homozygous, all of her sons and 50% of her daughters are affected. Affected individuals are related to one another through their maternal family. Y-linked inheritance It is a rarest type of inheritance in which only males are affected. The disease transfers from father to son. As expected, all sons inherit this feature from their father, but no daughters. Y-linked inheritance is also called holandric inheritance. Examples include hypertrichosis of the ears (hairy pinna), porcupine man and webbed toes. Salient features of Y-linked inheritance Y-linked inheritance occurs only in males. It usually appears in all sons of males. It is absent in daughters as the father cannot transfer the Y-linked genes to the daughters. The daughters appear normal phenotypically. Daughters cannot become the carriers of the disease trait.