Classical Genetics

Since the beginning of the human history,people have wondered how traits are inherited from one generation to next.Although children look more often like one one parent than the other,most offspring seem to be a blend of the characteristics of both parents. Centuries of breeding of domestic plants and animals had shown that useful traits----speeds in horses,strength in oxen and larger fruits in crops---can be accentuated by controlled in mating.However,there was no scientific way to predict the outcome of a cross between two particular parents.

It wasn't until 1865 that an Augustinian monk named Gregor Mendel found that an individual traits are determined by discrete "factors" later known as genes, which are inherited from your parents.

Genes come in pairs.Each alternative from of a trait is specified by alternative forms of gene. There are dominant traits and recessive traits.Dominant trait is the situation which one particular gene for a certain characteristic is dominant over the other.On the other hand,Recessive trait is a character of which will only be expressed if paired with similar gene.

Mendel believed that genes behave like atom that compose a pure substance.Genes can combine in various ways,but always maintain their distinct identities. For example, in a cross between two pure-bred parents with different traits, the hybrid offspring would have both gene alternates for each trait.Mendel proposed that although both gene alternates are present, there is no blending of gene because the gene alternate for a trait is "dominant" over the other. The recessive trait is seen whenever a single copy of its gene is inherited.When crossing the hybrid offspring,dominant trait reappears in the next generation.Mendel reasoned that the recessive trait is shown only when a copy of the recessive gene form is inherited from each parent.

When Mendel proposed that each trait is determined by a pair of genes, it presented a potential problem.If parents pass in both copies of a gene pair,then offspring would end up with four genes for each trait.Mendel deduced that sex cells contain only one parental gene of each pair. The half sets of genes contributed by sperm and egg cell restore a whole set of genes in the offspring. Mendel found that different gene combinations from the parents resulted in specific ratios of dominant to recessive traits. The results of a cross between two hybrid parents-each carrying one dominant and one recessive gene were key to his synthesis.Although Mendel's law were first tested in pea plants and fruit flies,evidence quickly mounted that they applied to all living things. Just as mutations had provided keys to understanding fruit fly genetics,Pedigrees of families affected by diseases provided many of the first examples of Mendelian inheritance in humans. Recessive inheritance was first described for the disorders: Alkaptonuria(1902) and Albinism (1903). Among the first dominant disorders discovered were: Brachydactyly(short-fingers,1905) congenital cataracts(1906), and Hunington's chorea (1913).Duchenne Muscular Dystrophy(1913),red-green color blindness (1914) and Hemophilia (1916) were the first sex-linked disorders. The simple concept of eye color inheritance: Brown is dominant,Blue is recessive was published in 1907; However, Scientists now believed that several genes are involved.

In many ways,Gregor Mendel was quite lucky in discovering his genetic laws.He happened to use pea plants,which happened to have number of easily observable traits that were determined by just 2 alleles.And for the traits that he studied in his peas,one allele happened to be dominant for the trait that and the other was a recessive form.Things aren't always so clear-cut and "simple" in the world of genetics,but luckily for Mendel,he happened to work with an organism whose genetic make-up was fairly clear-cut and simple.

What if Mendel were given a mommy black mouse and a daddy white mouse and asked what their offspring would look like? He would have said that a certain percent would be black and the rest would be white.He would have never even consider that a white mouse and a black mouse could produce a GRAY mouse! For Mendel,the phenotype of the offspring from parents with different phenotype always resembled the phenotype of at least one of the parents.In other words,Mendel is unaware of the phenomenon of the INCOMPLETE DOMINANCE.

I remember the example of our Biology teacher for this topic:

RED FLOWER X WHITE FLOWER = PINK FLOWER

In Incomplete dominance, a cross between two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.
It's like mixing paint.

RED + WHITE will make PINK.

Red doesn't totally block the white, Instead there is incomplete dominance and we end up with something in between.

CODOMINANCE

First, Let me point out that the meaning of the prefix "co-" is "together."

Cooperate =work together
CO habitat= Habitat together

The genetic gist to codominance is pretty much the same as incomplete dominance. A hybrid organism shows a third phenotype----not the usual "dominant" one and not the "recessive" one.. but a third, different phenotype. With incomplete dominance, we get a BLENDING of the dominant and recessive traits. In COdominance, the recessive and "dominant" traits appear together in the phenotype of the hybrid organism.

Example:

RED X WHITE = RED AND WHITE SPOTTED

You can see examples of codominance anywhere around.. You can see it in some animals especially in cats,cheetahs, tigers etc.

Well, hope your brain got a little bigger just like what happened to my brain when I learned about classical genetics. Whew! After learning these stuffs,, I really feel genius!! :p... Because maybe with these knowledge about classical genetics,maybe I could work with some scientists someday..(esp. if its about classical genetics stuffs.. ha ha!!) Let me share some experience that made me feel more genius! I proved to myself that in our house, when it comes to bio stuffs esp. in genetics, I'm the only person who knows much about these stuffs. I'm not being boastful,but its true! Maybe some of my classmates is experiencing this feeling too. OK.. let's go on with the story that I'm going to share. I have a cousin who lives nearby our house and one time, when I'm doing my assignment about Dihybrid cross she went to our house then I challenged her to try answering the questions, she replied,"Ano yan? Di ko alam yan eh!" When she told me that, I wanted to answer her back, "Duh.. Don't you know that? You're already in college right?!?!" but instead, I just laughed at her,, :) haha.. Well.. It really feels good when you know something that other people don't know! It makes you feel that you're genius! As if you know everything! haha... :))

Its really fun studying genetics! At first, I thought that it would be a hard lesson.. as in "nose bleed!" But I'm wrong.. really really wrong! I realized that genetics is just... easy! (but not all the time maybe..) When you're given a problem to solve to find out what would be the possible trait of their offspring,, Just have to analyze it.. and when you're done analyzing it, the rest will be just a Piece of cake! :p..
For some other people who'll read this post and haven't studied classical genetics yet, TRUST ME, it's not as hard as what you're thinking, but it's as easy as eating a piece of cake!

Life is so amazing that nature creates variations!Though we might have the same traits.. We still have different DNA(genetic material).. and you can never change that!

Everybody's different and no one else is you!


pOsTed by: ZyRa sHemItha QuierreZ