The feeling when your teacher asked you to write on a ¼
sheet of paper on what you know about Non-Mendelian Patterns of Inheritance and
the truth is you don’t have anything to write. What to do? What to do? …
Seriously, I don’t have an idea about that cause all I know is about the
Mendelian Inheritance. In that time all I can do is to guess that maybe it has
some point of connection with the Mendelian Inheritance in some ways. Well,
it’s only a wild guess in order to write something even a little to my paper. I’m
sure some students also felt that way in the same situation. After writing our
answer, we passed it to Ma’am Ruby and she started the discussion using a
Power-Point Presentation. Our teacher explained it to us clearly by giving us
the full description and some examples regarding each content of the topic. I
realized that listening to the teacher carefully and understanding very well
each term are very important in the comprehension of the lesson.
Hope you like it guys :) ;)
The picture above is Carl Correns, a German botanist and
genetist who discovered the Non Mendelian Inheritance in 1908. By the way,
after Ma’am Ruby discussed this topic, it really extended my knowledge about
Genetics. Before, I thought that the Mendelian Law of Dominance was the only
basis that genetist follow but I’m wrong because there comes the Non Mendelian
Inheritance wherein the patterns of phenotypes do not accord with those as
expected in Mendelian Laws on inheritance. Non Mendelian Inheritance includes
Incomplete Dominance, Co-Dominance, Pleiotropy, Multiple Alleles, Polygenic
Inheritance, Sex-Influenced Traits, Sex-Limited Traits, and Sex-Linked Traits. Let
me share to you what I have learned during the discussion and some examples.
Incomplete Dominance is where the hetero zygote condition is
intermediate between two extreme phenotypes. It has one allele code for the
active enzyme that affects the rate synthesis of anthocyanin pigment and the
other for the inactive enzyme. Like for instance, the hair of women are either
curly wavy, and straight because the amount of curl is determined by the number
of disultide bonds between keratin molecules.
Example of Incomplete Dominance through flower color:
In Co-Dominance, the hetero zygote condition manifests both
extreme phenotypes. The genotypic ratio is the same as the phenotypic ratio
like in the case of incomplete dominance. Co dominant alleles are written as
capitals with subscripts or superscripts. A good example of co dominance is
that of the roan coat as seen in some cattle and horses.
I also learned about Pleiotropy in which one gene pair has
many effects and the affected individuals may express different subsets of
symptoms that may superficially appear as if they are caused by different disorders.
One example of disorder is the Phenylketonuria (PKU)-a genetic disorder in
which the body can't process part of a protein called phenylalanine (Phe). Phe
is in almost all foods. If the Phe level gets too high, it can damage the brain
and cause severe intellectual disability.
Pleiotropy in
Individuals:
Our teacher also told us about
Multiple Alleles where there are at least three types of alleles for a
particular trait, with two alleles occupying a single locus at any given time. A
very good example of this is the fur color of the rabbit with a phenotype
Agouti, Chinchilla, Himalayan, and Albino. Here, dominance hierarchy may be
exhibited.
Inheritance of Blood Type:
I found out the differences among sex-influenced traits,
sex-limited traits, and sex-linked traits. Sex influenced traits are also
autosomal, meaning that their genes are not carried on the sex chromosomes.
Again, what makes these traits unusual is the way they are expressed
phenotypically. In this case, the difference is in the ways the two genders
express the genes. Sex limited traits are generally autosomal, meaning that
they are not found on the X or Y chromosomes. The genes for these traits behave
exactly the same way that any autosomal gene behaves. The difference here comes
in the expression of the genes in the phenotype of the individual. Sex-limited
traits are expressed in only one gender. Sex Linked Traits are traits whose
loci are literally on the sex chromosomes, so their transmission from
generation to generation is affected by the sex chromosome complement of the
individual. In any species with non-homologous sex chromosomes, these traits
can be significant. An example of this is a person with Hypertrichosis Pinnae
Auris in which the trait is passed along the male line. Another example of this
is the Hemophilia or the inability to clot blood.
A diagram on how Hemophilia are passed from the parents to the
offspring:
I was really nice learning all of these because it explains
how we attained the traits we have and the traits that others have in real life
situations. It answers our questions regarding where the traits came from not
only for humans but also for plants and animals. So this is also the reason why
genetic disorders occur through inheritance. :)
Certain students of
genetics inferred that the Mendelian units responsible for the selected
character were genes producing only a single effect. This was careless logic.
It took a good deal of hammering to get rid of this erroneous idea. As facts
accumulated it became evident that each gene produces not a single effect, but
in some cases a multitude of effects on the characters of the individual. It is
true that in most genetic work only one of these character-effects is selected
for study—the one that is most sharply defined and separable from its
contrasted character—but in most cases minor differences also are recognizable
that are just as much the product of the same gene as is the major effect.
