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Mendel's Work and
Laws
Who is Mendal?
Gregor Johann Mendel was a scientist, Augustinian friar
(catholic brother) and abbot of St. Thomas' Abbey in Brno,
Margraviate of Moravia. Mendel was born in a German-speaking
family in the Silesian part of the Austrian Empire (today's Czech
Republic) and gained posthumous recognition as the founder of the
modern science of genetics. Though farmers had known for
millennia that crossbreeding of animals and plants could favor
certain desirable traits, Mendel's pea plant experiments conducted
between 1856 and 1863 established many of the rules of heredity,
now referred to as the laws of Mendelian inheritance.
Mendel's Laws
Mendel was in charge of the monastery garden, he
conducted various experiments using garden peas that were
available for him, he conducted his experiments by allowing
different pea plants to fertilize each other.
Mendel concluded three laws of inheritance and those are :
1. Dominance
2. Segregation
3. Independent Assortment
The Law of Dominance
Mendel's Law of Dominance states that recessive alleles
will always be masked by dominant alleles. Therefore, a
cross between a homozygous dominant and a
homozygous recessive will always express the dominant
phenotype, while still having a heterozygous genotype.
As an example we have the crossing over of two traits,
the yellow coloured plant (T) and a green coloured plant
(t)
As we can see the dominant plant is the yellow trait
which will always be at a ratio of 3:1 in the F2 generation
The Law of Segregation
he Law of Segregation states that every individual organism contains
two alleles for each trait, and that these alleles segregate (separate)
during meiosis such that each gamete contains only one of the alleles.
An offspring thus receives a pair of alleles for a trait by inheriting
homologous chromosomes from the parent organisms: one allele for
each trait from each parent.
The Law of Independent Assortment
The Law of Independent Assortment states that alleles for separate
traits are passed independently of one another. That is, the
biological selection of an allele for one trait has nothing to do with
the selection of an allele for any other trait. Mendel found support
for this law in his dihybrid cross experiments (Fig. 1). In his
monohybrid crosses, an idealized 3:1 ratio between dominant and
recessive phenotypes resulted. In dihybrid crosses, however, he
found a 9:3:3:1 ratios (Fig. 2). This shows that each of the two
alleles is inherited independently from the other, with a 3:1
phenotypic ratio for each.
Figures
Figure 1
Figure 2
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