Page 61 - Biology - XII

EXPERIMENT - 11

Objective
Preparation and analysis of pedigree charts.

Principle/Theory
Pedigree is the study of a family for a particular trait/disease/defect. It helps us to predict accurately a trait
that is passed in future generation/children if related individuals are married. Thus, Mendelian concept of
inheritance—dominance and segregation of traits can be studied in human beings, also. Internationally
approved symbols for pedigree chart drawing is used. A careful study of the pedigree chart helps us to
understand whether the gene is—autosome linked in dominant/recessive, X-chromosome linked dominant/
recessive, Y-chromosome linked or not.
Pedigree Chart Traits

S. No. Type Explanation Traits
1. Autosome-linked Encoding gene present on any one of Brachydactyly, Polydactyly, Dimple
dominant traits the autosomes. And wild-type allele is in cheeks.
recessive to its mutant allele. Mutant
allele is dominant.
Males and females are equally aff ected.
2. Autosome-linked The mutant allele of a trait is recessive to Albinism
recessive traits its wild-type allele.
Males and females are equally aff ected.
3. Sex chromosome X-linked Encoding gene is present on Duchene muscular dystrophy (oral
dominant traits X-chromosome and its mutant allele is facial digital syndrome)
A rare trait dominant to its wild-type allele. Result: Absence of teeth, cleft/bifi d
tongue, mental retardation
4. Sex chromosome X-linked Encoding gene is present on Red green colour blindness,
recessive traits X-chromosome and its mutant allele is haemophilia
recessive to its wild-type allele.
Males express it even if they are hemizygous and females express the trait only when they are homozygous.
Aff ected persons are related to one another through the maternal side of their family.

5. Sex chromosome Encoding gene is present on Presence of hair on pinna
Y-linked traits Y-chromosome. It is present in all males. (hypertrichosis)

Only in males

1. Pedigree is the study of a family for a particular trait/disease/defect, etc.

2. It helps in accurate predictions concerning a trait in future children if related individuals or those
with a family history for such traits are married.
3. The fi rst step is to fi nd/know whether the trait in case study is dominant/recessive.

4. Above 4,000 human traits and diseases have been associated with specifi c genes.
5. Carriers cannot be identifi ed until an aff ected child is born to the carrier individual.
6. Recessive traits are frequently expressed in which father and mother are closely related.

7. Sex-linked (X-linked) recessive traits from pedigree analysis can be identifi ed as—the trait frequently
occurs in males, trait is transmitted to grandsons of an aff ected male through his daughter. It is never

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