Histogram:
A graphic representation of frequency distribution is called a histogram. To form a histogram from the frequency distribution of heights, the various heights are marked off on the horizontal axis and rectangles are erected to represent the various classes.
Looking at the histogram, it can be concluded that the height of 68 inches is most common whereas the number of individuals declines towards either end. Thus in polygenic inheritance, the extreme phenotypes are rare and the intermediate ones are more frequent.
Histogram for Frequency Distribution of Characters in Monogenic Inheritance:
In a monohybrid Mendelian segregation, the two parents belong to two distinct phenotypic classes:
- Homozygous Dominant
- Homozygous Recessive
In F1 due to the dominance of one allele over the other entire progeny shows only a dominant phenotype. In F2 generation, the dominant and recessive characters (phenotypes) segregate out in the ratio of 3:1.
Histogram for Frequency Distribution of Characters in Polygenic Inheritance:
In Polygenic Inheritance, the parents fall into two distinct categories.
- F1 progeny
- F2 progeny
F1 progeny shows an intermediate character because dominant genes are lesser in number in F1 generation. The F2 progeny exhibits a wide range of variation so that a continuous curve is obtained in F2 generation.