Post by laurcat on Jan 25, 2013 18:47:43 GMT -5
So we've learned about simple Mendelian genetics, and also a little bit of non-Mendelian genetics (Dihybrids). Today I will teach you more about non-Mendelian genetics. I am squeezing incomplete dominance and codominance in the same lesson.
Now, you know that the dominant allele rules over the recessive, and two of the same dominant alleles will, of course, give you the dominant trait. But what if you had two dominant alleles...that were different?
Incomplete Dominance-
In kindergarten, you learned that blue and red made purple. It may sound too simple to be true, but when a blue and red variety of some flowers are crossed, their offspring is purple. This is called incomplete dominance. Both the alleles for blue and red are dominant (BR), but neither shows. What shows is an intermediate trait- something that goes in between. However, crossing a purple-flowered plant with a red-flowered plant will not in turn get you a maroon plant. Remember that there are only two possible alleles, and the alleles of those plants will only cross each other to make one of the three possible colors.
Now, in New Germany, not only could you have straight, black hair, but you could also have shiny, dull, or glittery hair. Not just your typical shiny, metallic shiny, so we'll call the allele for shiny M, and dull will be M'. The allele for dull is spoken as 'M prime'- the apostrophe is called a 'prime'. Noticed that these alleles are both capital letters, therefor they are both dominant. Now, you can probably guess that crossing someone with shiny hair and someone with dull hair will have glittery hair-an intermediate trait-as the result of incomplete dominance. The allele combination for glittery hair, of course, is MM'.
Fill out the Punnett square below. The parent on top has glittery hair, and the parent on the side has shiny hair.
Once you've filled it out, answer these:
# of offspring with MM genotype:
# of offspring with M'M' genotype:
# of offspring with MM' genotype:
Do any of the offpspring have dull hair?
Is it possible for any of the offspring's children to have dull hair?
The answers:
# of offspring with MM genotype: [glow=red,2,300]2[/glow]
# of offspring with M'M' genotype: [glow=red,2,300]0[/glow]
# of offspring with MM' genotype: [glow=red,2,300]2[/glow]
Do any of the offpspring have dull hair? [glow=red,2,300]No.[/glow]
Is it possible for any of the offspring's children to have dull hair? Yes. If one of the children with the genotype MM' is crossed with someone who is M'M' or MM', their children could have dull hair. All it takes is one M' allele from each parent.
Codominance-
With incomplete dominance, we had two dominant traits that combined to create an intermediate trait. Codominance is where you have two different dominant traits that both appear together.
Blood types are a good example. You can have a blood type that is A, B, AB, or O. (Ignore the positives and negatives for now.)
The alleles for these blood types are represented by the letter 'I', and for the dominant ones, the 'I' is also accompanied by a superscript.
A=dominant: IA IA, IA i
B=dominant: IB IB, IB i
O=recessive: ii
I think you can figure out that IA i and IB i are heterozygous dominant.
Now, Susashleem has the genotype IB IB, so she's homozygous for blood type B. Her husband, Davidshlemmen, is IA i, heterozygous for blood type A.
Here is the example Punnett square:
Look at the boxed gentoypes. When IA and IB were combined, they formed IAIB. This is the genotype for type AB, and an example of codominance. In incomplete dominance, neither trait showed, but rather created an intermediate trait. In codominance, both dominant traits show. If you have blood type A, certain molecules will be on the surface of your blood cells. Blood type B is a different set of molecules, and blood type O is no molecules. Blood type AB is an example of codominance because both the molecules from type A and type B are on the surface your blood cells.
So now I conclude my genetics series. Just ask me for help if you or your dolls need it! I have no life, I'll be able to find time to help. XD
Now, you know that the dominant allele rules over the recessive, and two of the same dominant alleles will, of course, give you the dominant trait. But what if you had two dominant alleles...that were different?
Incomplete Dominance-
In kindergarten, you learned that blue and red made purple. It may sound too simple to be true, but when a blue and red variety of some flowers are crossed, their offspring is purple. This is called incomplete dominance. Both the alleles for blue and red are dominant (BR), but neither shows. What shows is an intermediate trait- something that goes in between. However, crossing a purple-flowered plant with a red-flowered plant will not in turn get you a maroon plant. Remember that there are only two possible alleles, and the alleles of those plants will only cross each other to make one of the three possible colors.
Now, in New Germany, not only could you have straight, black hair, but you could also have shiny, dull, or glittery hair. Not just your typical shiny, metallic shiny, so we'll call the allele for shiny M, and dull will be M'. The allele for dull is spoken as 'M prime'- the apostrophe is called a 'prime'. Noticed that these alleles are both capital letters, therefor they are both dominant. Now, you can probably guess that crossing someone with shiny hair and someone with dull hair will have glittery hair-an intermediate trait-as the result of incomplete dominance. The allele combination for glittery hair, of course, is MM'.
Fill out the Punnett square below. The parent on top has glittery hair, and the parent on the side has shiny hair.
Once you've filled it out, answer these:
# of offspring with MM genotype:
# of offspring with M'M' genotype:
# of offspring with MM' genotype:
Do any of the offpspring have dull hair?
Is it possible for any of the offspring's children to have dull hair?
The answers:
# of offspring with MM genotype: [glow=red,2,300]2[/glow]
# of offspring with M'M' genotype: [glow=red,2,300]0[/glow]
# of offspring with MM' genotype: [glow=red,2,300]2[/glow]
Do any of the offpspring have dull hair? [glow=red,2,300]No.[/glow]
Is it possible for any of the offspring's children to have dull hair? Yes. If one of the children with the genotype MM' is crossed with someone who is M'M' or MM', their children could have dull hair. All it takes is one M' allele from each parent.
Codominance-
With incomplete dominance, we had two dominant traits that combined to create an intermediate trait. Codominance is where you have two different dominant traits that both appear together.
Blood types are a good example. You can have a blood type that is A, B, AB, or O. (Ignore the positives and negatives for now.)
The alleles for these blood types are represented by the letter 'I', and for the dominant ones, the 'I' is also accompanied by a superscript.
A=dominant: IA IA, IA i
B=dominant: IB IB, IB i
O=recessive: ii
I think you can figure out that IA i and IB i are heterozygous dominant.
Now, Susashleem has the genotype IB IB, so she's homozygous for blood type B. Her husband, Davidshlemmen, is IA i, heterozygous for blood type A.
Here is the example Punnett square:
Look at the boxed gentoypes. When IA and IB were combined, they formed IAIB. This is the genotype for type AB, and an example of codominance. In incomplete dominance, neither trait showed, but rather created an intermediate trait. In codominance, both dominant traits show. If you have blood type A, certain molecules will be on the surface of your blood cells. Blood type B is a different set of molecules, and blood type O is no molecules. Blood type AB is an example of codominance because both the molecules from type A and type B are on the surface your blood cells.
So now I conclude my genetics series. Just ask me for help if you or your dolls need it! I have no life, I'll be able to find time to help. XD
