Monohybrid Cross - Inheritance of One Gene

Introduction

A type of biological inheritance known as Mendelian inheritance adheres to the ideas that Gregor Mendel first put forth in 1865 and 1866, which were later rediscovered in 1900 by Hugo de Vries and Carl Correns and made popular by William Bateson. These ideas were initially debatable. Mendel's theories became the foundation of classical genetics when Thomas Hunt Morgan combined them with the Boveri- Sutton chromosomal hypothesis of heredity in 1915. Two organisms sharing a similar genetic locus but have vid alteration combines to form a monohybrid cross. The control of trait is studied in monohybrid cross that is due to two or more mutations at a single gene. Each parent in such a hybrid must be homozygous, or true breeding, for the desired trait. A cross's eligibility as a monohybrid cross is frequently assessed using the monohybrid ratio, commonly referred to as the distribution of second-generation (F2) offspring.

Definition of a Monohybrid Cross

This cross comprises two homozygous individuals that have the opposing phenotype for a certain genetic characteristic.

"A monohybrid cross is a cross between two monohybrid characteristics (TT and tt)."

It is in charge of passing one gene on. Punnett Square is a good visual demonstration of it. Geneticists utilize monohybrid crosses to study the expression of heterozygous genes passed down from parents to homozygous offspring.

Experiment

Mendel investigated seven different characteristics in pea plants which can be as follows −

• Texture of a seed that is either round or wrinkled.

• Color of the seed that is either yellow or green.

• Color of the flower that is either white or purple.

• Growth that is either tall or dwarf.

• Shape of pod that is either pinched or inflated.

• Color of the pod that is either green or yellow.

• Axial or terminal position.

Mendel’s Experiment on Pea

• To detect if the cross is monohybrid, a pair of pea plants is used by Mendel with two unique characteristics—one tall and one dwarf.

• As a result, cross-pollination of tall and dwarf plants was observed in all tall plants.

• All of the hybrid plants were rather tall.

• A progeny of Filial1 or F1 were the offspring, and the name of the generation is the first hybrid generation (F1).

• He also found that the F1 offspring had a single behavioral pattern, i.e., they acted like one of the parents, in an experiment that included all seven potential pairings. There was not a single another parent character.

• He was steadfast in his efforts to encourage self-pollination in F1 line plants.

• Surprisingly, he discovered that, even though the other three plants were tall, one of them was a dwarf.

• Tall plants outnumbered small plants three to one.

• There had been no mixing, as per his allegation that no offspring were of intermediate height.

• Because the results were identical for other plant components, the offspring were dubbed Filial2 or F2 progeny. He called them the second hybrid generation.

• Mendel noticed that traits from the F1 generation were different of F2.

• He distinguished between dormant and dominant qualities.

• Furthermore, he came to the conclusion that some "factors" are passed down the generations from father to child.

• These "factors" were later referred to as "genes."

• Genes govern how qualities are handed down from generation to generation.

• A gene is made up of two alleles, each of which codes for a particular trait. Homozygous allele pairings have identical features, such as TT or tt, whereas heterozygous pairs have unique or non-identical traits, such as Tt.

Examples

Huntington Disease

• It is a deadly genetic disorder.

• Every individual carries the mutated Huntingtin gene, which causes this disease

• The homozygous recessive huntingtin gene in an individual was linked with another person's homozygous dominant huntingtin gene.

• Each child contained Huntington's disease dominant allele. As a result, children will be affected by this illness.

Verifying Dominant Behavior

• Monohybrid crossings between homozygous people are often merely the initial stage, however.

• It is possible to determine whether a characteristic is dominant or recessive via heterozygous crosses, in which both parents possess a dominant gene and a recessive allele.

• This second stage is modelled after the procedure that Gregor Mendel used with peas.

• Scientists cross two parents with genotype Ll who have long stems in common for example. In a perfect world, one out of every four of their progeny would have the genotype ll and a short stem.

• Scientists may safely conclude that long stems are a dominant characteristic in this second iteration since they appear more often than short stems.

Conclusion

Mendel's theories became the foundation of classical genetics when Thomas Hunt Morgan combined them with the Boveri-Sutton chromosomal hypothesis of heredity in 1915. In his 1930 book, “The Genetical Theory of Natural Selection”, Ronald Fisher coupled these concepts with the theory of natural selection, giving evolution a mathematical foundation and laying the groundwork for population genetics in the current evolutionary synthesis. Mendel investigated one gene inheritance and the inheritance of two or more than two genes in the garden pea plant (Pisum sativum). "The Inheritance of One Gene" (monohybrid cross). The outcome shows how different and similar a character can be on the basis of their inheritance.

Correns devised the famed three principles of inheritance −

• The Law of Dominance

• Law of Segregation, and

• Law of Independent Assortment.

After examining the findings of Mendel's research.

The Law of Dominance states that the recessive allele expression is suppressed in heterozygotes.

The Law of Segregation explains why a character's gametes are pure and there is no mixing of alleles in heterozygotes.

FAQs

Q1. What does one gene inheritance entail?

Ans. The mode of the single gene inheritance (one pair of alleles) ruling a single character is known as the inheritance of one gene. It is also known as a monohybrid cross and monogenic inheritance.

Q2. State the different types of inheritance.

Ans. There are basically four types of inheritance which are codominance, incomplete dominance, multiple allelism, and sex-linked inheritance.

Q3. State the laws that determine the outcome of the inheritance of a single gene?

Ans.

• The Dominance Principle

• The Act on Segregation