Pedigree Charts
Exercise 11
Aim: Preparation and analysis of Pedigree Charts
Principle: The Mendelian concept of dominance and segregation can also be studied in humans by preparing and then analysing the pedigree charts. The internationally approved symbols for indicating males and females, marriages, various generations (I, II, III), etc., are given below.
Requirement: Information about characters/traits in a family for more than one generation
Procedure
Select a family in which any one of the monogenic traits such as tongue rolling, widow's peak, blood groups’, red-green colour blindness, dimple in
LABORATORY MANUAL: BIOLOGY
the cheek, hypertrichosis of ear, hitch-hiker's thumb, etc., is found. Ask the person exhibiting the trait to tell in which of his/her parents, grand parents
(both maternal and paternal), their children and grand children the trait in question is present. Among surviving individuals the trait may also be examined. The information made available is the basis for the preparation of pedigree chart using the appropriate symbols. A careful examination of the pedigree chart would suggest whether the gene for the character is autosomelinked dominant or recessive, X - chromosome linked dominant or recessive,
Y- chromosome linked or not.
Explanation
1.
Autosome Linked Dominant traits: These are the traits whose encoding gene is present on any one of the autosomes, and the wildtype allele is recessive to its mutant allele, i.e., the mutant allele is dominant. The pedigree-chart can be of the undernoted pattern (Fig. 11.2), where the female being interviewed is exhibiting the trait, and is indicated by an arrow-mark in the chart.
The characteristic features of inheritance of such type of traits are:
(a) Transmission of traits occurs from parents of either sex.
(b) Males and females are equally affected.
(c) The pedigree is vertical, i.e., the trait is marked to be present in each of the generations.
(d) Multiple generations
Aim: Preparation and analysis of Pedigree Charts
Principle: The Mendelian concept of dominance and segregation can also be studied in humans by preparing and then analysing the pedigree charts. The internationally approved symbols for indicating males and females, marriages, various generations (I, II, III), etc., are given below.
Requirement: Information about characters/traits in a family for more than one generation
Procedure
Select a family in which any one of the monogenic traits such as tongue rolling, widow's peak, blood groups’, red-green colour blindness, dimple in
LABORATORY MANUAL: BIOLOGY
the cheek, hypertrichosis of ear, hitch-hiker's thumb, etc., is found. Ask the person exhibiting the trait to tell in which of his/her parents, grand parents
(both maternal and paternal), their children and grand children the trait in question is present. Among surviving individuals the trait may also be examined. The information made available is the basis for the preparation of pedigree chart using the appropriate symbols. A careful examination of the pedigree chart would suggest whether the gene for the character is autosomelinked dominant or recessive, X - chromosome linked dominant or recessive,
Y- chromosome linked or not.
Explanation
1.
Autosome Linked Dominant traits: These are the traits whose encoding gene is present on any one of the autosomes, and the wildtype allele is recessive to its mutant allele, i.e., the mutant allele is dominant. The pedigree-chart can be of the undernoted pattern (Fig. 11.2), where the female being interviewed is exhibiting the trait, and is indicated by an arrow-mark in the chart.
The characteristic features of inheritance of such type of traits are:
(a) Transmission of traits occurs from parents of either sex.
(b) Males and females are equally affected.
(c) The pedigree is vertical, i.e., the trait is marked to be present in each of the generations.
(d) Multiple generations