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Mendelism
【Dominance/Recessiveness and the Punnett Square】
Mendel had found when cross-fertilizing tall true-breeding species with dwarf
true-breeding species, all F1 hybrids presented tall pea plants. Next, allowing these F1
hybrids to self-fertilize produces F2 hybrids, but tall and dwarf pea plants presented
together this time and the ratio between tall and dwarf plants was approximately 「3：
1」. It was the same case when observing other characters. As a result, Mendel called
the traits shown in the F1 generation as「dominance」and the traits later shown in F2
generation as 「recessiveness」.
Fig.1： Experiments with garden peas
Eventually, Mendel, who sought knowledge tirelessly, decided to carry out an
experiment to observe two characters at one time, and he also found a special ratio
close to「9：3：3：1」. Afterwards, scientists utilized the Punnett square to verify
Mendel＇s discoveries and continued using them till now.
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Fig.2： Experiments with garden peas
Seven characters: flower color (purple or white), stem length (tall or dwarf), flower
position (axial or terminal), seed color (yellow or green), seed shape (round or
wrinkled), pod color (green or yellow), pod shape (inflated or constricted); the former
are all「dominance」, the latter are「ecessiveness」.
Fig.3： Seven characters of peas
【Father of Genetics---Mendel】
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Since a long time ago ranchers or farmers had known how to breed better species.
However, there’s no theoretical basis all along and even the contemporary scientists
had no definite general genetic rules to explain the hereditary phenomena . On the
advent of 1856, a priest from Austria carried out a series of experiments with pea
cross-fertilization in a abbey garden and gradually disclosed the mysterious veil of the
hereditary phenomena. This priest is exactly the Father of Genetics---Mendel.
【Mendel's Experiments with Garden Peas】
By good luck, Mendel chose pea plants as his experimental material, in that there
were a large number of stable species among pea plants and they could reproduce by
self-fertilization ( self-pollens were transmitted to self-styles ). Making use of the
quality that pea plants could do self-fertilization, Mendel firstly removed immature
anthers (a region producing pollens) and spread pollens from another plant to the pea
plants without anthers. As a result, Mendel could confirm the parental generation of
each pea sub-generation. Besides, Mendel only observed one character at a time (e.g.,
round or wrinkled). He observed and recorded seven characters in total. By virtue of
his specialty in mathematics and statistics, he finally obtained a specific hereditary
ratio.
【Medelian Inheritance】
Fig.4：Mendel
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1. Characters are determined by a pair of hereditary factors: one comes from the
father and the other comes from the mother (called as an allele).
2. As「dominant」and「recessive」hereditary factors appear at the same time, the
dominant characters are expressed; the recessive characters are expressed when both
hereditary factors are recessive.
Hereditary factors are randomly assigned to sperms or ova and the probabilities are
both the same (law of segregation and law of independent assortment).
Reviewed by：Zhang, Yong-Ta professor
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