This Class 12 Biology Practical focuses on the study of prepared pedigree charts to understand the inheritance of common genetic traits. Students learn how traits like tongue rolling, blood groups (A, B, AB, O), widow’s peak, and colour blindness are passed from one generation to the next. By analysing pedigree symbols and patterns, learners can identify dominant, recessive and sex-linked traits. This practical helps build strong concepts of genetics, supports exam preparation, and improves scientific interpretation skills. Ideal for CBSE and all state boards, this activity is an essential part of the Class 12 Biology practical file.

AIM: To Study of prepared pedigree charts of genetic traits such as rolling of tongue, blood groups, widow's peak and colour blindness.

REQUIREMENTS:

Questionnaire about a particular disorder, a family with genetic disorder for more than one generation, paper, pencil, etc.

PROCEDURE:

The careful examination of chart would suggest whether the gene for the character is

i. A. Autosome-linked dominant or recessive

ii. X-chromosome linked dominant or recessive

iii. Y-chromosome linked or not.

Explanation of Each Trait

A. Autosome Linked Dominant Traits

i. The encoding gene of this trait is present on any one of the autosomes.

ii. The mutant allele is dominant and the wild type allele is recessive for such traits

iii. In this pedigree chart, the female being interviewed is exhibiting the trait and is indicated by an arrow mark in the chart.

iv. Transmission of trait occurs from any of the parent.

v. Male and female are equaly affected. e.g., Widow' Peak.

Widow's Peak

It is a 'V'-shaped hairline across the forehead. it is a dominant trait. Thus, both homozygous dominant(A) and heterozygous (Aa) individuals have widow's peak, while homozygous recessive (aa) individuals have a straight hairline.

B. Autosome Recessive Traits

i. In this, mutant allele is recessive to its wild type allele,

ii. These traits occur in equal proportions in male and female siblings, whose parents are carriers of the allele, i.e., they have only a single copy of the allele and therefore they are normal.

iii. The siblings are homozygous for the defective allele, but their parents, though some may appearnormal are obviously heterozygous, i.e, are merely carriers of the trait.

iv. The marriage between man and woman genetically related with each other, occasionally results in the appearance of such traits, e.g, albinism and rolling of tongue

The Rolling of Tongue

Some persons are able to roll their tongue in U-shape. The inability to roll the tongue is caused by autosomal recessive allele "a', Thus, both homozygous dominant (AA) and heterozygous (Aa individuals are able to roll the tongue, while homozygous recessive (aa) individuals are unable to rol their tongue in this way.

x- Linked Recessive Traits

i. These are the traits whose encoding gene is present on the X-chromosome and its mutant allele is recessive to its wild type allele.,

ii. The females expresses the trait only when they are homozygous for the mutant allele whereas, males does so even when they are hemizygous for it.

iii. About half of the sons of the carier (heterozygous for the trait) females are affectecd.

iv. In case of homozygous females showing the trait, 50% of her daughters and all of her sons are likely to be affected. Therefore, it can be concluded that males are most affected population in this category.

v. Affected persons are related to one another through the maternal side of their family.

vi. Any evidence of male to male transmission of the trait rules out the X-linked inheritance.

vii. Examples are haemophilla and red-green colour blindness

Colour blindness

The colour blindness is a sex-linked recessive disorder of humans. In this, the affected individual is unable to differentiate between red and green colours. It results in the absence or malfunctioning of one or more of the three types of cone cell responsible for colour vision.

Pedigree analysis of colour blindness

Blood group inheritance