Introduction

Mendel conducted his studies on the pea plant in the garden, which possesses total dominance of characteristics or alleles, proving the rules of heredity. Other researchers conducted studies on many animals and plants and discovered deviations from Mendelian ratios. Gene interactions, a new pattern of inheritance, were identified as a result of these studies and observations. This study is recognised as Post–Mendelian genetics or Neo-Mendelian genetics.

It’s worth noting that Mendel focused on qualitative inheritance, which involves complete dominance.

A qualitative trait is exhibited qualitatively, which implies that the phenotype can be classified into many groups. These categories do not have to be in any particular sequence.

Table of Contents

Mendelian Inheritance

Gregor Mendel proposed the concepts of Mendelian inheritance in 1865 and 1866, which were rediscovered in 1900 by Hugo de Vries and Carl Correns and popularised by William Bateson.

We refer to the inheritance principles established by Gregor Mendel, referred to as Mendelian laws, while today’s geneticists refer to them as Mendelian principles or Mendelian rules because there were many deviations grouped under the umbrella phrase Non-Mendelian inheritance.

Mendel’s Laws of Inheritance

  • Law of Dominance and Uniformity: Some of the alleles are dominant, while some are recessive, and an organism with one dominant allele would exhibit the dominant allele’s influence.
  • Law of Segregation: Each gene’s alleles segregate from one another during gamete production, leaving each gamete with only one single allele for each gene.
  • Law of Independent Assortment: During the production of gametes, genes for various traits can segregate independently.

Also Read: Mendel’s Laws of Inheritance

Qualitative Inheritance in Genetics

A qualitative trait is one that can be classified into one of several categories. For example, coat colour dilution, horned or polled, and black or red coat colour are all qualitative characteristics. Qualitative traits are often governed by one or a few genes, indicating that they are inherited traits.

Qualitative Inheritance Characteristics

  • The inheritance of qualitative features with two different expressions, such as tall and dwarf pea plants, is referred to as qualitative inheritance or monogenic inheritance.
  • A single pair of opposing alleles control each character.
  • Every single character has two separate contrasting features, i.e. two different phenotypes.
  • Whether the character is regulated by one or both dominant genes, the degree of expression stays the same.
  • Single-effect genes have been discovered.
  • Environmental factors have no effect on it.
  • It reveals a discontinuous sequence of inheritance.
  • Individuals from the F1 generation have a strong resemblance to the dominant parent.
  • The F2 generation has a 3:1 ratio of individuals. There is no expression in the middle.
  • It is concerned with single matings and their offspring.
  • Counting and finding ratios can be used to analyse this inheritance.
  • Qualitative features like pea plant height, seed coat, and colour are examples of inheritance.

Qualitative Traits in Humans

Blood type is an example of a qualitative trait in humans. Rh-positive or Rh-negative blood can be found in humans. We have a positive blood type if we possess the gene coding for the Rh protein in our body (A positive, B positive, O positive, etc.). If we don’t have the gene, our blood will not contain Rh, and we will have a negative blood type (A negative, B negative, etc.). Outside of these two distinct alternatives, there is no “in-between” or variety.

Quantitative Inheritance or Polygenic Inheritance

More than two or two gene pairs determine these characteristics, which have a cumulative or an additive influence. Cumulative genes, multiple factors or polygenes are the names given to these genes. Polygenes are phenotypic traits that are influenced by two or more separate pairs of non-allelic genes residing on different loci and have a cumulative or additive effect.

A polygenic character, also known as a quantitative character, is a phenotypic trait regulated by more than one pair of genes. Continuous variation can be shown in polygenic or quantitative features. Galton (1883) anticipated that in the human population, characteristics such as height, skin colour, and IQ would display continuous expression changes rather than just two contrasting expressions.

In plants, the height of an oak tree is an example of a quantitative trait. The sawtooth oak tree, for instance, can grow to reach 40 to 60 feet tall. That means the tree might be any height between 40.1 and 50.76 feet and 57.01 feet tall.

Difference between Qualitative and Quantitative Genetics

Qualitative genetics and quantitative genetics are terms used to describe the study of qualitative and quantitative traits in general. The following are the main differences between the two:

Qualitative Genetics vs Quantitative

Qualitative Genetics

Quantitative Genetics

Characters of kind

Characters of degree

Distinct phenotypic classes; discontinuous variation.

Variation is continuous, and phenotypic measures create a spectrum.

Effects of a single gene

Single gene effects are too minimal to be recognised under polygenic control.

Individual matings and their offspring are a source of concern.

Concerned with a population of creatures that includes all types of mating.

Counts and ratios are being used to analyse the data.

Assessments of population parameters like the mean and standard deviation are provided via statistical analysis.

Round or wrinkled pea seeds, horned or hornless cattle, and black or white guinea pig coats are all examples of qualitative genetics.

Crop productivity, weight gain in animals, and blood pressure are all examples of quantitative genetics.

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Frequently Asked Questions (FAQs)

Q1

Why is skin colour a quantitative inheritance?

Multiple genes determine human skin colour. As a result, it is an example of quantitative inheritance, also known as polygenic inheritance, in which multiple genes control a phenotypic trait. Polygenes, or cumulative genes, are genes that control many features.

Q2

Define “trait” in biology.

In common usage, a “trait” refers to any quality that a person possesses, such as a personality trait or the way they act. However, the biological definition of a trait is more specific. A trait is a property defined by your genetic composition in biology. Biological features in persons include hair colour, eye colour, height, blood type, and hairline.

Q3

Can two blue-eyed parents have a brown-eyed child?

Yes, parents with blue eyes can produce a child with brown eyes. Inheriting two copies of the brown-eyed gene is the only way to have brown eyes. On the other hand, blue-eyed parents can pass on a recessive brown-eyed gene to their child. As a result, a brown-eyed baby could be born from two blue-eyed couples.

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