Dominant and Recessive Traits


 
 
Concept Explanation
 

Dominant and Recessive Traits

Notations used in Mendel’s experiments:

The dominant trait is usually represented by a capital letter. For example, tallness is represented by ‘T’ and dwarfness is represented by the corresponding small letter ‘t’. If tallness is due to a pair of dominant alleles, it is written as TT. If tallness is due to only one dominant allele, it is written as Tt. If both the alleles are recessive, making the organism dwarf, then it is written as tt. A homozygous condition is one in which both the alleles are of the same nature, e.g., TT or tt. A alleles are of different nature, e.g., Tt. When two heterozygous condition is one in which the characters are taken into account, the notation for the homozygous dominant could be AABB, and for the homozygous recessive it could be aabb. He performed following two experiments:

1. Inheritance of Traits for one Contrasting Character:

Mendel took pea plants with different characteristics such as height (tall and short plants).

  • The progeny produced from them (F1 -generation plants) were all tall. Mendel then allowed F1 progeny plants to undergo self-pollination.
  • In the F2-generation, he found that all plants were no three quarter were tall and one quarter of them were short. This observation indicated that both the traits of shortness and tallness were inherited in F1 -generation, but only the tallness trait was expressed in F1 -generation. This is known as the law of dominance.
  • Two copies of the traits are inherited in each sexually reproducing organism. TT and Tt are phenotypically tall plants, whereas tt is a short plant. For a plant to be tall, the single copy of ‘T’ is enough. Therefore, in traits Tt, ‘T’ is a dominant trait while ‘t’ is a recessive trait. In F2 - generation, both the characters are recovered, though one of these is not seen in F1 stage. During gamete formation, the factor or allele of a pair segregate from each other. This is known as the segregation.
  • 2. Inheritance of Traits for Two Visible Contrasting Characters:

    Mendel took pea plants with two contrasting characters, i.e. one with a green round seed and the other one with a yellow wrinkled seed.

  • When the F1 progeny was obtained they had round and yellow seeds, thus establishing that round and yellow are dominant traits.
  • Mendel then allowed the F1 progeny to be self-crossed (self-pollination) to obtain F2 progeny. He found that seeds were round yellow, round green, wrinkled yellow and some were wrinkled green.
  • The ratio of plants with above characteristics was 9:3:3:1, respectively (Mendel observed that two new combinations had appeared in F2).
  • In F2-generation, all the four characters were assorted out independent of the others. Therefore, he said that a pair of alternating or contrasting characters behaves independently of the other pair, i.e. seed colour is independent of seed coat. This is known as the law of independent assortment.
  • Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    A typical genotypic (hidden) monohybrid ratio is ________________

    Right Option : B
    View Explanation
    Explanation
    Question : 2

    Cross between F1 Generation and recessive parent is ___________________

    Right Option : C
    View Explanation
    Explanation
    Question : 3

    ___________________ took pea plants with different characteristics to study dominant and recessive traits.

    Right Option : A
    View Explanation
    Explanation
    Chapters
    Cytology
    Classifucation Of Plants
    Structural Composition Of Plants
    Nutrition In Plants, Harmones And Plant Disease
    Ecosystem
    Classification In Animals
    Nutrition In Animals
    Human Digestive System
    Human Respiratory System
    Human Skeleton System
    Human Excretory System
    Human Nervous System
    Human Circulatory System
    Human Endocrine System
    Human Reproductive System
    Genetics
    Human Diseases
    States Of Matter
    Metals And Non Metals
    Acid Bases And Salts
    Periodic Classification
    Fuel, Combustion And Flame
    Environmental Chemistry
    Rest And Motion
    Work Power And Energy
    Gravitation
    Pressure And Its Effects
    Simple Harmonic Motion
    Sound and Waves
    Heat And Temperature
    Light - Reflection
    Electricity And Magnetism
    Modern Physics
    Force And The Laws Of Motion
    Light - Refraction
    Dispersion And Human Eye
    Magnetic Effect Of Electric Current
    Atom And Molecule
    Pre-Historic Period
    Indus Valley Civilization
    Vedic Civilization
    Religious Reform Movement
    The Early Kingdoms
    The Mauryan Empire
    Post Mauryan Period
    The Age Of The Guptas
    Post Gupta Era
    Age of Rajput
    Khilji Dynasty
    Slave Dynasty
    Tughlaq and Sayyid Dynasty
    Vijaynagar Empire And Bahamani Kingdom
    Mughal Empire And Beyond
    Lodhi Dynasty
    Cholas, Chalukyas and Pallavas
    Arab Invasions
    Bhakti and Sufi Movement
    Rise of Sikhs, Jats and Marathas
    Administrative Structure of Delhi Sultanate
    Architecture During Medivial India
    Advent Of The Europeans
    Post Mughal Period
    Rise of New States in 18th Century
    Growth of British Paramountacy
    Socio Religious Reforms
    Constitutional Development of India
    Indian Struggle Against British Rule
    The Revolt Of 1857
    Education Under British Rule
    Role of Press in Freedom Struggle
    First Phase of National Movement
    Second Phase of National Movement
    Third Phase of National Movement
    Constitutional Development in India
    Constituent Assembly
    Union And Its Territory
    Structure of Indian Constitution
    Fundamental Rights and Duties
    The Union Executive
    The Union Legislature
    Constitutional Amendments and Provisions
    Judiciary In India
    Emergency Provisions
    Center - State Relations
    The State Executive
    The State Legislature
    Election Commission Of India
    Constitutional Organisation
    Non-Constitutional Organisation
    Local Self Goverment
    India - Size And Location
    Geological History Of India
    The Physical Features Of India
    Climate Of India
    Soils In India
    Natural Vegetation
    Windlife Conservation In India
    Drainage System of India
    Irrigation System Of India
    Agriculture In India
    Livestock And Fisheries In India
    Minerals And Energy Resources In India
    Means Of Transport In India
    Major Industries In India
    Tribes of India
    Census of India 2011
    Music
    Dance
    Theatre
    Pantings
    Art, Architecture & Culture of India
    Bio-Diversity
    Earth And Its Structure
    Land Rock And Soil
    Atmosphere, Climate And Weather
    Oceanography
    Human And Regional Geography
    Economic Growth And Development
    Sectors Of Indian Economy
    Economic Planning Of India
    Fiscal And Monetary Policy In India
    Infrastructure In India
    Effects Of British Rule On Indian Economy
    National Income
    Banking System In India
    Poverty And Unemployment
    Inflation And Trade Cycles
    Major Institutions
    Environmental Studies
    Chemistry In Everyday Life
    Units And Dimensions
    Tissues In Organism
    Content / Category
    Class / Course
     
     


    Students / Parents Reviews [20]