The key difference between Punnett square and pedigree is that Punnett square displays all possible genotypes that can be inherited from two parental genotypes while pedigree represents the family history of a particular trait, especially the inheritance of a gene.
Punnett square and pedigree are two types of tools that help to determine the probability of inheritance of genes. Both show the likelihood of inheriting a particular trait to offspring. In other words, both predict patterns of inheritance in family lines. Hence, they can help to determine the risk of an inherited disease in a child. Punnett square is simply a graphical way of showing all possible genotypes that can occur in children from the two parents.
CONTENTS
1. Overview and Key Difference
2. What is Punnett Square
3. What is Pedigree
4. Similarities Between Punnett Square and Pedigree
5. Side by Side Comparison – Punnett Square vs Pedigree in Tabular Form
6. Summary
What is Punnett Square?
Punnett square is a tool that shows all the possible genetic outcomes of a cross. In other words, Punnett square is a graphical way of showing all possible genotypes from two-parent genotypes. Reginald Punnett created the concept of Punnett square in the early 1900s. In genetics, Punnett square is often used to illustrate the principles of Mendelian inheritance. There are two types of Punnett squares. One illustrates a monohybrid cross which shows single trait determined by one locus. Therefore, it has only four boxes. The second one is larger, and it follows two traits, and there are sixteen boxes.
Figure 01: Punnett Square
Punnett square helps to determine the child’s risk of inheriting a genetic disease from their parents. Moreover, Punnett square is useful in breeding programs to select organisms with specific traits for continued breeding. However, Punnett square is unable to explain the phenomenon of genetic linkage. Moreover, Punnett square cannot predict the inheritance patterns of some traits that are influenced by several genes and environmental factors.
What is Pedigree?
A pedigree chart represents the genetic family history of a particular trait. It is useful to determine the risk and presence of a disease in the next generation. Hence, the purpose of pedigree is to analyze the inheritance of a particular trait among the members of the same family. This analysis is usually done for three generations or more.
Figure 02: Pedigree Analysis
In the pedigree analysis, marriages are represented by lines. Males are represented by boxes, while females are represented by circles. If the analyzing trait is present in any individual, it is represented in black, or it is shaded. Moreover, it reveals whether the trait is dominant or recessive. Furthermore, it indicates whether the trait resides in the autosomes or sex chromosomes. The pedigree shows the mode of inheritance of a trait in the family. Most importantly, pedigree helps to identify haemophilia or colour blindness in advance in the coming generations.
What are the Similarities Between Punnett Square and Pedigree?
- Both Punnett square and pedigree show the inheritance of a trait coded by a gene.
- Both assume that traits are inherited independently.
- Both can help to determine the risk of an inherited disease in a child.
- They can indicate the genotypes and phenotypes of the offspring.
- In addition, they can confirm whether the trait is dominant or recessive.
What is the Difference Between Punnett Square and Pedigree?
Punnett square is a square diagram that shows all possible genotypes of a particular cross or breeding experiment while pedigree is a chart that shows the inheritance pattern of a particular trait, especially a disease through a family. So, this is the key difference between Punnett square and pedigree. Furthermore, a Punnett square represents a cross, either a monohybrid or dihybrid cross, while pedigree represents generations of a human family, especially three or more generations of the same family.
Below infographic shows more details of the difference between Punnett square and pedigree.
Summary – Punnett Square vs Pedigree
Punnett square is a graphical way of showing all possible outcomes of a cross. Therefore, it is useful to predict the genotypes resulting from a monohybrid or dihybrid cross. In contrast, pedigree analysis is a chart that shows the inheritance pattern of a trait (gene) in three or more generations of a family. Hence, the pedigree chart is useful to trace the inheritance pattern of genetic disease through a family and generations. Thus, this summarizes the difference between Punnett square and pedigree.
Reference:
1. “Punnett Squares | Protocol”. Jove.Com, 2020, Available here.
2. “Punnett Square: Definition & Example.” Study.Com, 2020, Available here.
Image Courtesy:
1. “Punnett Square” By Pbroks13 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Sex linked inheritance” By Simon Caulton – Own work (CC BY-SA 3.0) via Commons Wikimedia