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PinkMonkey Online Study Guide-Biology
Mendel conducted his experiments in three stages.
. Stage-1 : It involved selecting a pair of parents with contrasting characters
and obtaining each parent plant in pure condition ,i.e,. breeding true for
the characters selected.
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For example, Mendel ensured that the plant selected
for round seeds produced only round seeds on self-fertilization
and the plant selected for wrinkled seeds produced only wrinkled
seeds . Such pure, true-breeding parents were obtained by Mendel
through repeated self fertilizing, generation after generation.
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Stage -2 : It involved crossing of the selected parents.
Of the pair, one plant was used as the male parent and the other as the
female parent. Pollen from the male was dusted on the stigma of the female
parent for cross-pollination. Mendel conducted reciprocal crosses also.
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For example : in one cross, the round seeded
variety was used as the male parent and the wrinkled seeded variety
as the female parent, while in the reciprocal cross of the same
parents, the wrinkled variety was used as the male parent and the
round seeded variety as the female parent. This may be represented
as follows :
Male Parent Female Parent
Cross - I Rounded seeded Wrinkled seeded
Reciprocal Cross Wrinkledd seeded Rounded seeded
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Such a cross between two parents representing contrasting forms
of a single character is called monohybrid cross and the
offspring is called a hybrid. The hybrid represents the first
filial generation or F1
generation.
Stage - 3 : In the third stage, Mendel allowed
each F1 hybrid to self-pollinate and produce
the next, i.e., Second Filial generation or F2
generation.
Mendel conducted a similar type of hybridization experiment
separately for each of the seven pairs. He meticulously maintained a complete
record of the actual number of each type of offspring in every generation
(i.e., data of qualitative as well as quantitative results).
Mendel observed that in each of these crosses, all the F1 hybrids resembled only one parent, while the character of the other parent was not seen in the F1 hybrid. For example, in a cross between round X wrinkled type, the F1 were all round seeds only. The wrinkled character was not seen. The character which appears in the F1 hybrid was termed dominant and the other as recessive by Mendel. Thus, in each of the seven pairs, one form is dominant and the other is recessive (See Table 1.1). The F2 progeny showed presence of both parental forms which always appeared in the ratio of 3 dominants : 1 recessive. This 3:1 F2 ratio was termed as the monohybrid ratio.
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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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