Co-dominance and Incomplete Dominance

I know youre on the edge of you seats. When does the "dominant always appears over recessive" rule not apply?

Im glad you sort-of asked.

Co-dominance and Incomplete dominance are similar in the way that both traits influence the phenotype of an offspring, but different in the way where Co-Dominance has both traits appear and Incomplete dominance allows the traits to blend.

Incomplete dominance:
Say you have a flower that has three different phenotypes, white, blue and purple.
Lets say red is recessive, or ww, and blue is dominant, or WW.
The punnet square of heterozygous parents here would look like this:

The purple flowers, or the Ww heterozygous flowers, blended the trait from the dominant blue trait and the recessive red trait to make purple!

Co-dominance:
Unlike incomplete dominance, co-dominance has both traits appear, so instead of the flowers blending color, they both are shown:

Instead of the traits blending together to make q new color, they both appear on the flower.

F2 Generation Outcomes

So whatever happened in the F2 generation?

As we know from our first punett square, each of the offspring had the genotype Tt, which would appear as tall because the T masks the t.

Mendel then allowed this offspring to self-pollinate, or have the offspring's anthers (male organ) to ferilize the stigma (female organ). This would cause the same genotype to be mixed:

      T    t
T  TT  Tt
t   Tt    tt

WOAH. The four offspring have quite a mix of genotypes, including the homozygous (the same type of allele) dominant, the homozygous recessive, and the heterozygous (one of each type of allele). The same rule applies though, the dominant trait (at least in this case) will always show over the recessive. So, if you look at all of your options from the offspring, they are the following:

TT- Homozygous dominant,, will appear as tall
Tt- Heterozygous, will appear as tall
Tt- Heterozygous, will appear as tall
tt- Homozygous recessive, will appear as short.

This explains how the second generation of Mendel's appeared 75% with the dominant trait, tall, and 25% the recessive trait, and sums up the basics of genetics that Mendel found.

Gotta go. More basics tomorrow!

I've returned. Under my blankets and pillows. Judging by the stuffiness of this hiding spot, I dont have much oxygen to spare. So I'll make this quick.

Where was I.

AH Punett squares, yes.

The parents, as you may recall, were tall and short. Say you have an offspring recipe, and in order to make it you need two parts tall and two parts short. These "parts" are what we call alleles, the parts of a gene, which are given by the parents of the offspring.

With Punnet squares, this arangement of alleles would look like this, where tall is represented by a T and short is represented by a t:

Tall Plant: TT
Short Plant: tt

The tall plant in this case is dominant, or greater than the short plant, because it has two T's that will mask the other t's. The short plant is recessive, or less than the taller one.

In this case, the punett square would look like this:

   T    T
t  Tt   Tt 
t  Tt   Tt

Now, all the alleles are arranged into new genes: Tt, the genotype (the genetic makeup of the offspring).

But what does that mean? We couldn't possibly have a mixing of  alleles, BOTH traits would appear!

Not necessarily. While it is possible in some cases (stay tuned) it isn't in this case.

Because the T is still dominant and will mask the t, the T or tall trait will appear. This is why in Mendel's first generation, ALL the plants appeared as tall, or the phenotype (the trait that actually appears).

Well, now I'm absolutely exhausted. I'll tell of the F2 generation tomorrow.

The Basics of What Mendel Found

While almost as genius as I, Mendel found the following after cross-pollinating a short pea plant with a tall one (which I did not do), or the  P1 Generation. All of these parent's offspring had the same dominant (or trait that masks another) trait.

After finding this, Mendel then allowed the F1 generation, or the first generation, to self-pollinate. This resulted in the F2 generation, or the second generation, to produce 75% of the plants to be tall, and 25% to be short.
How curious, one might say.
WRONG.
Its quite simple, actually.
You see, punnet squares (or as I like to call them, party squares. They're just so much fun!) show how this mix of heights is possible.
Er...perhaps ill explain at another time. Mum is yelling for me to "Quit that typing racket." and "I know youre still awake, Jacob." 
Bye.

Gregor Mendel, the ORIGINAL father of Genetics. (a.k.a. my hero)

Gregor Mendel, the father of genetics and my ultimate hero when it comes to genetic science. Studying pea plants, Mendel found the laws of dominance, segregation, and independent assortment all through the height, pea shape, pea color, flower color, and many more traits of the plants. The basics of his findings inspired (and helped) scientists, such as my handsome self, know the basics of heredity. Him and I couldve been best friends. Curse my being born in this era.