Prepared pedigree charts of any one of the genetic traits such as rolling of tongue, blood groups, ear lobes, widow's peak and colour blindnes

Aim: Prepared pedigree charts of any one of the genetic traits such as rolling of tongue, blood groups, ear lobes, widow's peak and colour blindness

Theory:

1. A record of in heritance of certain genetic traits for two or more generation presented in the form of a diagram or family tree is called as pedigree

2. In pedigree, a square represents a male, a circle represents a female, solid symbol represents traits under study and a cross or shade (of any type) in the symbol signifies the carrier of recessive allele.

3. Parents are shown by horizontal line while their offspring are connected to it by vertical line.

Autosomal Dominant Trait:

Blood Groups, Free hanging earlobes, Widow's Peak, Rolling of tongue. The encoding gene for these genes is present on any of the autosomes. In these traits, the mutant allele is dominant.

Such type of traits exhibits the following features:

• The traits get transmitted from the parents to either gender.
• It affects males and females equally.
• The trait is present in each of the generations, i.e., the pedigree is vertical.
• Some common traits of this type include blood groups, polydactyly, brachydactyly, the dimple in cheeks, etc.

Autosomal Recessive Trait

The mutant allele of such traits is recessive.

Salient features of such type of traits include:

1. It is found equally in multiple male and female siblings whose parents are carriers.
2. Homozygous siblings for defective alleles, but parents are heterozygous.
3. If men and women who are genetically related are married to each other, they might exhibit this trait.

X-Linked Dominant Traits

The encoding gene for such traits is located on the X chromosome. The mutant allele is dominant in this trait.

The features of such type of traits are:

1. Inheritance is vertical and is found in all the generations.
2. If the female is affected, half of her sons are also affected.
3. If the male is affected, all the daughters will be affected but no sons will be affected, i.e., there is no male-to-male transmission.

X-Linked Recessive Traits- Colour Blindness

In humans, color blindness is caused by a recessive sex-linked allele. Examine the pedigree of color-blindness below. On the diagram, label the genotypes of every individual. Note: If the gene is on the Y chromosome (Y-linked), we would write it as Y^b, and a male with this trait would be written as XY^b .If the allele is on the X chromosome (X-linked), we would write it as X^b, and a heterozygous female would be X^BX^b (1 pt)

In such type of traits, the mutant allele is recessive to the wild type allele. The features of X-linked recessive traits include:

1. This is expressed only by homozygous females but homozygous and hemizygous males.
2. If the female is the carrier, about half the sons are affected. If the female is homozygous, 50% of the daughters and 100% of the sons can be affected. That is why the male population is the most affected.

Y-chromosome Linked Traits

The gene for such traits is present on the Y-chromosome. Any trait linked to Y-chromosome is found only in males and not in females because the Y-chromosome is present only in males. All the sons of the affected male exhibit the trait, whereas, none of the daughters exhibits the trait.

Material/Apparatus Required:

Information about traits in a family for more than one generation

Procedure:

1. Select a family with anyone of the monogenic traits like rolling of tongue, blood groups, ear lobes, widow's peak, and colour blindness.

2. Ask the person exhibiting the trait as to who in his/ her family has the trait in question.

3. Prepare a pedigree chart on the basis of the information collected, using appropriate symbols.

4. Examine the pedigree chart carefully to find out whether the disease is autosomal recessive, autosomal dominant, X-linked dominant or recessive, and Y-linked dominant or recessive.

Results:

Pedigree charts explains the genetic traits.