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PinkMonkey Online Study Guide-Biology

Reasons for Mendelís success:

i.    Mendel concentrated on the results of one trait at a time.
ii.   When the behavior of one trait was established, only then       he considered two characters together.
iii.   He conducted a large number of crosses (2000-3000) to       eliminate the chance factor and to obtain a valid and       accurate explanation
iv.   Most of all, he actually counted the number of offsprings       of each category and maintained accurate records for each       generation in each experiment.
v.   However, luck played a major role in his success (though       Mendel did not know this fact) in the selection of pea       plants as well as in the selection of those particular seven       pairs of contrasting characters. Because, luckily for       Mendel, in each pair, one form of the character is       completely dominant over the other. Moreover, these       seven characters are present on seven different       chromosomes in the pea plant.  However, Mendel was       unaware of this fact.


In nature, there are several instances of incomplete dominance also. In such cases, the hybrid shows haracter intermediate between the two parents.  For example, in snapdragon, when a parent plant with red flowers is crossed with another having white flowers, the F1  hybrids show pink flowers.

         Parents        Red Flower       X          White Flower
                                                      ¯
         F1  hybrid                   Pink Flowers

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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