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PinkMonkey Online Study Guide-Biology

7.2 Mendelís Experiments on Sweet Pea

Selection of the material : Mendel selected garden sweet pea (Pisum sativum) for his hybridization experiments for of the following reasons : (i) Plants are annual and easy to cultivate. (ii) Peas have many distinct, well-defined and easily observable morphological characteristics (traits). (iii) Flowers are bisexual and naturally self-fertilizing, but they can also be easily cross-fertilized. (iv) The offspring of cross-fertilized plants are fertile. (v) Flowers are sufficiently large for easy emasculation (removal of stamens) and artificial cross-pollination.

Selection of characters (traits) : Mendel selected 14 different varieties of the pea and grouped them into seven pairs. Each pair was considered for a specific trait (characteristic) such as flower color or seed shape or stem length, etc. The two members of each pair showed contrasting forms of the chosen trait, ,e.g., in a pair selected for stem length, one variety had a tall stem (6-7 feet tall) while the other had a dwarf stem . These seven pairs of contrasting traits are shown in Table 1.1.


Table 1.1 : Showing seven pairs of contrasting characters selected by Mendel

BIOBIOBIO

Sr. No.

Characters

Contrasting pairs (Allelic pairs)

(Dominant)

(RecBIOe)

1.

Form of seed

Round (R)

Wrinkled(r)

2.

Color of cotyledons

Yellow(Y)

Green(y)

3.

Color of seed coat

Colored(C)

White(c)

4.

Form of pod

Inflated (I)

Constricted(i)

5.

Color of pod

Green(G)

Yellow(g)

6.

Position of flower

Axial(A)

Terminal(a)

7.

Height of plant (Length of stem)

Tall(T)

Dwarf(t)

Nature and procedure of the experiments : Mendel had very clear concepts of what he was doing and what requirements were necessary if he had to arrive at the conclusions accurately and successfully. He realized the necessity of: (i) using pure breeding parent plants; (ii) considering only one character at a time during the breeding experiments; (iii) always keeping the generations separate; (iv) and using statistical and mathematical principles to compute the obtained results properly.

Table of Contents

7.0 Introduction
7.1 Gregor Mendel
7.2 Mendel's Experiment on Sweet Pea
7.3 Terminology Used
7.4 Law of Dominance
7.5 Monohybrid Ratio
7.6 Law of Segregation
7.7 Dihybrid Ratio
7.8 Law of Independent Assortment
7.9 Test Cross or Back Cross
7.10 The Concept of "Factor"

Chapter 8





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