Pedigree Analysis: Definition, Methods, and its Importance For Class 12th, and NEET
Family studies have been employed in anthropological fieldwork and research for a very long time. It is regarded as a crucial technique in ethnographic research. Family studies help in understanding both the history of the family and the relationships among its members. Understanding a society’s social structure and network of relationships among its members also benefits from a family studies perspective.
The family and its members help in identifying a certain genetic characteristic that runs in the family. Pedigree analysis, which examines the inheritance pattern seen from mating lines, can be used to identify these human genetic features. The Latin words pes, which means “foot,” and grus, which means “crane,” are combined to form the word “pedigree,” which is used to denote lines of descent. Pedigrees are family trees that display the parents, children, and descendants along with the generations, as well as those who had special characteristics.
Pedigree Analysis: Definition
A Pedigree is a diagrammatic description of how a specific trait or traits are passed down genetically across two or more generations of biologically related people. In other words, it is the use of symbols and ancestral lines to symbolize the links between family members. It helps in putting family relationships into perspective, especially for big extended families. To ascertain how various genetic illnesses are inherited, it is frequently utilized. Drawing a family tree using common symbols allows one to trace their family history and better comprehend inheritance types. In a Pedigree, males and females are symbolized differently, and relationships are depicted using various line patterns. Additionally, several symbols are used to symbolize carriers of a genetic characteristic or those who are impacted by it.
Techniques and Importance of Pedigree Analysis
Understanding the nature of inheritance for a specific trait can be accomplished through pedigree analysis. Autosomal (recessive and dominant), X-linked (recessive and dominant), or Y-linked inheritance patterns are all possibilities. In the sections below, we’ll talk about a few of the inheritance patterns.
A) Autosomal Recessive Inheritance
The homozygous recessive alleles on the autosomal chromosome are what define autosomal recessive inheritance. Individuals with the homozygous autosomal recessive allele had the afflicted phenotype, and the matching autosomal dominant allele is thought to reflect the unaffected phenotype. Both male and female progeny are equally affected by this altered phenotype, which also shows in the offspring of unaffected parents. Both parents are required to carry the afflicted gene to create a recessive homozygote person. The likelihood of heterozygote carriers joining together determines whether an afflicted person develops. When relatives mate, this likelihood of being impacted rises. In comparison to mating between nonrelatives, mating between relatives increases the likelihood of developing an affected homozygous recessive trait. Therefore, a significant share of recessive disorders in human populations are brought about by first cousins or close family marriages. One such autosomal recessive disorder is albinism, which is brought on by a problem with the enzyme that produces melanin. Because the red haemoglobin pigment in the blood vessels in the retina is being revealed, the affected albinos have light-colored hair, lack of skin pigmentation, and pink eye pupils. For instance, an allele, let’s say ‘a,’ determines albinism, and ‘A,’ is the normal condition. The ‘albinos’ of the condition would have a genotype of ‘aa,’ whereas unaffected people would have either an AA or an Aa genotype.
The afflicted allele must have been present in both parents for a recessive homozygote to be conceived. The likelihood of heterozygote carriers joining forces usually determines whether an afflicted person is formed. When the relatives’ mating takes place, the likelihood of being impacted rises. The risk increases when relatives mate.
B. Autosomal Dominant inheritance
An autosomal dominant allele is what distinguishes autosomal dominant inheritance. In other words, while the aberrant allele is dominant, the normal allele is recessive. In autosomal dominant inheritance, the affected person often manifests in every generation since the aberrant allele they carry is a product of one of the affected parents. It implies that every affected person has at least one affected parent. All of the siblings can be impacted by either the mother or the father, but not both. The trait is equally passed on to boys and daughters by the affected parents. Achondroplasia, Huntington’s disease, Phenylthiocarbamide (PTC) taste, etc. are a few instances of autosomal dominant diseases that commonly affect humans.
C) X linked Recessive Inheritance
Affected phenotypes displayed sex differentiation in an X-linked recessive inheritance pattern. Usually, more males than females are afflicted. This is because only a mating in which both the mother and father carry the allele may create a female with the phenotype, whereas only a mating in which the mother contains the allele can result in a male with the phenotype. For instance, if the mother has the condition and the father is healthy, all of the sons will also have it, whereas only half of the daughters will have the condition. Sons will be born to a normal father and a carrier mother, with half of the sons being affected and the other half being normal. On the other side, none of the children are impacted when the mother is normal and the father has the condition. Since females inherit one of their X chromosomes from their fathers, all the daughters must be heterozygous “carriers,” even though all the sons will be healthy. Haemophilia, DMD, testicular feminization syndrome, and other conditions are typical examples of X-linked recessive illnesses in humans. Hemophilia, a condition in which a person’s blood cannot clot due to a lack of a protein called factor VIII, is likely the most well-known example of an X-linked recessive illness. The royal families of Europe have some of the most well-known haemophilia instances in their lineage.
For instance, the gene Xa determines haemophilia, and the allele XA determines the normal state. Male and female XaX and XaY, respectively, are the stand-in for the affected haemophiliac. For the trait to manifest in males, just one copy of the afflicted allele is needed. Females with one copy of the XAX and an afflicted allele do not manifest the illness phenotype. Such a person is referred to be a carrier of the illness, whereas a healthy, unaffected person would have the genotypes “XAX A” or “XAY” for males and females, respectively.
D) X linked Dominant Inheritance
One affected allele is enough to result in the condition in X-linked dominant inheritance. Both men and women are equally impacted by this kind of disease. In humans, it is an uncommon inherited illness. All of the affected males’ daughters inherit the trait, but none of their sons do. Half of the sons and daughters of affected females who marry unaffected males inherit the illness characteristic. Hypophosphatemia, a kind of vitamin D-resistant rickets, Rett syndrome, fragile X syndrome, and others are some of the more typical human X-linked dominant illnesses. For instance, the existence of the XD allele determines the presence of hypophosphatemia. A person with hypophosphatemia is symbolized by the letters XDX d, XDX D, and XDY. The disease phenotype can only be expressed by one allele. Men and women are both equally impacted. For males and females, respectively, XdX d and XdY indicate the typical genotype.
E) Y-linked Inheritance
Sex-specificity applies to the Y-linked inheritance. Due to the Y chromosome’s exclusivity in normal males, inheritance of this Y-linked genetic characteristic is only seen in males. In females, these characteristics are not seen. All boys inherit the Y chromosome from their fathers, so if the father has a condition, all of his sons will also have that condition. No daughter of the parents will inherit this chromosome. Only men are affected by the phenotype of this genetic characteristic. Y-linked disease, such as infertility, is one of the more prevalent types. For instance, the presence of the ‘I’ allele, often known as ‘XYI,’ is what causes Y chromosomal infertility. All of their boys, but not any of their daughters, are affected by the condition when a father is affected.
Finding the cause of a disease phenotype that runs in the family can be done by looking at the family pedigree. Additionally, it aids in estimating the likelihood that specific future occurrences will likely take place. To identify the inheritance of genetic disorders, pedigree analyses are utilized in newborn genetic testing. Additionally, it is useful for screening before symptoms show up and for testing heterozygotes (carriers). Hereditary counsellors use the pedigrees of certain families to help them in educating families who might be at risk for a variety of genetic diseases.
When using pedigree reasoning, there are five points to keep in mind.
(1) No allele of a dominant trait can be present in an unaffected person. (because each individual is impacted by a single allele of a dominant characteristic).
(2) It is presumed that anyone marrying into the family has no disease alleles, meaning they will never be afflicted and cannot ever carry a recessive trait. (Due to the rarity of the character in the population)
(3) A recessive characteristic can be carried by an unaffected person who carries one of the alleles. (because a recessive trait requires two alleles to manifest in an individual)
(4) A male can be impacted by an X-linked characteristic with just one recessive gene. The man is hemizygous, which means that he only possesses one allele of an X-linked trait.
(5) A father’s daughters inherit his X-linked gene allele, but not his sons. An X-linked gene allele is passed from a woman to both her daughters and sons.