12th Biology Practical ~ (Part B)10. to study the prepared Pedigree charts of genetic trades such as rolling of tongue, window's speak, blood groups and colour blindness.

12th Biology practical book answers pdf Maharashtra board 

~  (Part B) To study the prepared Pedigree charts of genetic trades such as rolling of tongue, window's speak, blood groups and colour blindness.

Introduction:

A pedigree is a list of ancestors showing genetic relationships between members of a family.

A record of inheritance of certain genetic traits for two or more generations presented in the form of family tree or a diagram, is called pedigree chart. Study of pedigree chart provides a strong tool, which is used to trace the inheritance of a specific trait, abnormality or disease in a family. In a pedigree chart specific symbols that are used, are indicated below.

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

 

Requirements: Prepared pedigree charts of genetic traits.

 

Procedure: Observe the given pedigree chart and write comments on it.

 

1. Inability to roll the tongue:

The rolling of tongue is the ability of a person to roll the tongue inwards in 'U' shaped as shown in the following figure. The inability to roll the tongue, is caused by autosomal recessive allele 'a'. Both homozygous dominants (AA) and heterozygous (Aa) individuals are able to roll the tongue while homozygous recessive (aa) individuals are unable to roll the tongue.

 

 

Comment on the given pedigree chart with respect to:

1. Inheritance of trait

Autosomal inheritance & the individuals are (autosomal), recessive (aa) which are unable to roll the tongue

2. Number of normal, carriers and affected progeny

Normal-7, carrier-o, affected-2.

3. Linkage – sex linked or autosomal

Linkage – autosomal

 

 

 

2. Widow's Peak

Widow's peak is a V- shaped hair line across the forehead. It is a dominant autosomal trait. The gene responsible for widow's peak is dominant 'W'. Therefore, both homozygous dominant (WW) and heterozygous (Ww) individuals have widow's peak, while homozygous recessive (ww) individuals have straight hair line. This feature is observed with both men and women.

 

 

 

 

Comment on the given pedigree chart with respect to:

1. Inheritance of trait

Autosomal dominant Inheritance

2. Number of normal, carriers and affected progeny

Normal - 3, Carrier - 0, Affected – 6. 2 males are normal in 2^nd generation whereas 1 male and 2 female are normal in 3^rd generation.

3. Linkage - sex linked or autosomal

Linkage autosomal.

 

 

3. Human blood groups:

1. The blood groups in human beings are described as per ABO system of classification.

2. The gene I (isoagglutinogen) controls the ABO blood groups.

3. It has three alleles I^A, I^B and i (recessive)

4. The alleles I^ and I not produce any surface antigen on R.B.Cs.

5. Each individual possesses only two alleles out of three.

6. Alleles l^A and I^B are co- dominant. Individually they are completely dominant over allele i.

7. There are six different genotypes and four different phenotypes with blood groups which are seen as follows:

 

 

 

 

Comment on the given pedigree chart and give the genotypes of the blood groups of individuals marked in blank box numbers - 2, 4, 8, 9, 12, 13:

-In the above pedigree chart, female ē blood group AB marries ē male having blood group A produces 4 progenies in which 1 daughter ē blood group A, one daughter has Blood group B and one son has A blood group, one daughter is with blood group AB

-When O blood group having female marries ē male having blood group B produces one son ē blood group B and 2 sons ē blood group

-When female having blood group A, marries with male having blood group B, produces female ē blood group O and male ē AB

-Genotype: (2) I^AI^O, (3) I^BI^O, (8) I^AI^O, (9) I^BI^O, (12) I^OI^O, (13) I^BI^A

 

 

4. Colour blindness:

1. Colour blindness is a sex / X linked recessive disorder of humans.

2. Due to recessive gene present on X chromosomes, colour sensitive cone cells are not formed. This results in red-green colour blindness.

3. It is more common in male than female.

4. It follows criss-cross inheritance as this trait is transmitted from the father to the grandson through his carrier daughter.

 

 

 

Comment on the given pedigree chart with respect to:

1. Inheritance of trait

-It is a sex linkage inheritance showing X-linked recessive disorder in humans.

-It follows criss-cross inheritance as this disease is transmitted from grandfather to grandson via carrier daughter

2. Number of normal, carriers and affected progeny

3 sons are normal whereas 3 daughters are carrier in first generation.

In 2 generation two daughter and one son is with normal vision, one daughter is carrier whereas one son is colourblind.

3. Linkage sex linked or autosomal Colour-blindness is a sex-linked inheritance as it passes from affected grandfather to his grandson through (heterozygous) carrier.

 

 

Questions

1. What is pedigree?

A record of inheritance of certain genetic traits for two or more generations presented in the form of Family tree or diagram called as pedigree

 

2. Why x-linked disorder are more common in male than in the female?

X-linked genes are located on non-homologous region of on chromosome. In female, both chromosomes are XX. Therefore, if recessive gene is present on one X-chromosome, then it is suppressed by dominant X-chromosome.

But in male, as only one X-chromosome is present, there is no dominant gene on Y-chromosome to suppress its effect

 

3. What are holandric traits?

The traits which are controlled by the genes which are present on non-homologous regions of Y-chromosome are called as holandric traits.

 

4. Give an example of autosomal recessive disorder in humans.

Inability to roll the tongue is an example of autosomal recessive disorder in humans.

 

Q. 5. Explain the concept of co-dominance with respect to ABO system in humans.

-In co-dominance, both genes/alleles of an express themselves equally in f₁ hybrids.

-In ABO blood group system, the gene I has three alleles as I^A, I^B, I^O. Each individual possesses only two alleles out of three

-Alleles I^A and I^B are dominant.