Day 27 -- Incomplete Codominance (..WHAT???)

As with every perfectly acceptable concept, we learned several ways to make genetics and crosses more complicated: we added CODOMINANCE and INCOMPLETE DOMINANCE !!

Of course we had to add something like this. After doing the Punnet Square, usually we have recessive traits (two small letters) or dominant traits (two large letters or one and one). However, with this amazing addition, the Heterozygous traits (Aa) now express a different trait, or a combination of the two. 

When red and white flowers are combined and the traits could possibly express incomplete dominance, the RRxrr cross results in all heterozygous flowers. While normally this would mean "all reds that carry the recessive trait," the resulting flowers now express the incomplete "pink" color due to their heterozygous nature. If you cross the pink with another pink, the chance would be 1 Red : 2 Pink :1 White, because a RR dominant or rr recessive could result from that cross. In short, the incomplete dominance means that neither is completely dominant, and there may be a cross between the two (Red and White make Pink).

On the other hand, codominance finds some way to express both traits in the case of heterozygous recipients. Imagine the red and white flower cross above. With the codominance, this time, the Rr offspring would be white with red spots (or red with white spots). This is very similar, but both are expressed in some way in the offspring. 

Also, sometime in this time period we learned about pedigrees. When looking at a cool graph thing with boxes and circles, we have to decide several factors in determining a trait's passing motion. For example, we have to check whether the trait is sex-linked or autosomal first. This requires running through the parents of one of the recipients with a Punnet Square of XX x XY. If the trait doesn't roll that way, then it is autosomal. At that point, we determine if it is linked to the dominant trait or the recessive by placing it into another Square. If all goes well, we can determine how it is passed down by the recipients from the Punnet Square.