Preparing Pedigree Charts of Any one of the Genetic Traits

You must have heard about the royal disease. Queen Victoria of England was a carrier of haemoglobin B. She passed this trait of haemophilia B to her three children out of nine. Do you know about pedigree? A pedigree is a record of the inheritance of some genetic traits for two or more generations in the form of a diagram called a pedigree. Now this pedigree chart is used to find out these inherited disorders. That's why close relatives are advised to not marry. Because it may lead to the expression of some recessive characteristics.

Table of Content

• Aim

• Articles Required

• Theory

• Procedure

• Observations

• Result

• Precautions

• Lab Manual Questions

• Viva Questions

• Practical Based Questions

• Conclusion

Aim

The experiment aims to prepare and study pedigree charts of any one of the genetic traits such as rolling of tongue blood groups, earlobes, widow's peak, and colour blindness

Articles Required

Information about the above-mentioned traits in the family

Theory

Pedigree 

Pedigree is the record of genetic traits for two or more generations in the form of a family tree.

There are different symbols used for human pedigree. Some of these symbols are explained below: 

Symbols used in pedigree analysis

Different symbols used for pedigree analysis

• A square represents male 

• Circle represent female 

• Parents are represented by horizontal lines whereas 

• Children are represented by the vertical line 

• The shaded symbol represents a trait under study

• Each generation is represented by roman numerals.

Procedure 

• Select a family with any one of the traits such as ear lobes, widow peak, colour blindness, blood group

• Ask questions from family members who exhibit these traits in their family

• Prepare a pedigree chart based on information collected from the family

• Then at the end examine the pedigree chart carefully whether traits are autosomal, sex-linked, recessive, or dominant

Problem 1- Inability to Roll Tongue

The trait of inability to roll the tongue appears in the progeny due to recessive genes. Now we have to find out the possible genotypes of these family members.

Pedigree chart

Solution: Now we can see in this pedigree chart that the father has the trait of the inability of rolling the tongue so the genotype of the father in 1st  generation is homozygous recessive. Now one of the children in 2nd generation has this trait so she must be homozygous recessive and the remaining children in 2nd generation are heterozygous recessive. So mothers in the 1st generation would be heterozygous recessive. Now, the 2nd child in the 3rd generation has this trait, so she would be homozygous recessive. 1st Children of the 3rd generation would be heterozygous recessive and 3rd, 4th, and 5th children of the 3rd generation may be heterozygous or homozygous.

It is an example of an autosomal recessive pedigree. 

Solution of pedigree chart of inability to roll tongue trait

Problem 2 -  Widow Peak

The pedigree chart for a particular family is given below. Indicate whether the shaded symbols belong to dominant or recessive traits. 

Pedigree chart of widow peak trait

Solution: Since the shaded symbols appear in all offspring, the father must be homozygous dominant and the mother homozygous recessive because in all other cases the possibility is absent. All the members of the 2nd generation will be heterozygous. This is further confirmed by the marriage of II-I with homozygous recessive-bearing children of both parental types. Marriage of II-3 with the homozygous recessive can produce both recessive and heterozygous. 

Solution of widow peak trait

Observations

Genotypes of various members of the family for a particular trait have been observed.

Results 

The pedigree charts of two families have been studied.

Precautions

First, carefully analyse the family tree and then write the genotypes.

Lab Manual Questions

Q1. What is a pedigree?

Ans: A pedigree is a record of the inheritance of a particular trait over two or more generations in a given family.

Q2. What does a horizontal line represent in a pedigree?

Ans: Horizontal line represents parents in a pedigree.

Q3. What is the importance of pedigree analysis?

Ans: Pedigree analysis helps in knowing the possibility of the presence of a particular trait in a homozygous or heterozygous state in family members.

Viva Questions

Q1. What is pedigree analysis?

Ans: It is a process of analysing the inheritance pattern of a family member over several generations to show the origin of a trait.

Q2. What is the conclusion of pedigree charts?

Ans: Pedigree chart can conclude the pattern of inheritance, it helps to find out whether the given trait is dominant or recessive or autosomal or sex linked trait.

Q3. What is linkage? 

Ans: Linkage is defined as the closeness of genes to one another on the chromosome. The more the closeness between the genes on a chromosome, more will be the linkage.

Q4. What are mendelian disorders? 

Ans: Mendelian disorders are the disorders that appear due to abnormalities in genes, or chromosomes. Examples of Mendelian disorders are cystic fibrosis and sickle cell anaemia.

Q5. What is the purpose of pedigree?

Ans: The main purpose of a pedigree chart is to analyse or find out the pattern of inheritance of a particular trait in a given family.

Q6. Give an  example of an autosomal dominant pedigree 

Ans: Autosomal dominant diseases include - Huntington's chorea and marfan syndrome.  In Huntington's disease nerve cells of the brain break over time.

Q7. Colour blindness pedigree chart given in practical book is dominant or recessive?

Ans: Colour blindness is a X- linked recessive disorder.

Q8. What is a pedigree chart called?

Ans: Pedigree chart is also called a family tree.

Practical Based Questions

Q1. What does the symbol square represent in a pedigree analysis?

1. Female

2. Male

3. Both

4. None of the above

Ans: 2. Male

Q2. What are different types of genotypes? 

1. Homozygous dominant

2. Homozygous recessive

3. Heterozygous

4. All of the above

Ans: 4. All of the above

Q3. What does the circle represent in pedigree?

1. Male

2. Twin

3. Female

4. None of the above

Ans: 3. Female

Q4. What does horizontal line represent in a pedigree?

1. Children

2. Marriage

3. Divorce

4. All of the above

Ans: 2. Marriage 

Q5. What does a vertical line represent in a pedigree?

1. Marriage

2. Children

3. Separation

4. None of the above

Ans: 2. Children 

Q6. What are genes made of?

1. DNA

2. Protein

3. Carbohydrates

4. All of the above

Ans: 1. DNA

Q7. What are the sources of genetic variation?

1. Recombination

2. Mutation

3. Both of the above

4. None of the above

Ans: 3. Both of the above

Q8. There are how many alleles of a gene? 

1. One

2. Two

3. Three

4. None of the above

Ans: 2. Two

Conclusion

• We have discussed pedigree and pedigree analysis in this experiment. 

• Different symbols used for the pedigree analysis also discussed in this experiment

• There are many types of genetic disorders, such as homozygous, heterozygous, dominant, and recessive

• Two problems of pedigree were also discussed in this experiment, inability of rolling tongue and widow peak.