Looking for people using Schaum's Genetics

[alleycat9]

Hi,

I was looking for people using Schaum's Genetics (4th edition) for review

I can post specific questions when I have them, but thought it might be good to find people using this particular book, since many of the questions in here are good practice, I think.

Right now, the question I am wondering about is re: co-dominance and incomplete dominance.

Question: There are white chickens and there are black birds. When you cross them, they make slate blue offspring. When slate blue's cross with themselves, you get white:blue:black 1:2:1.

Based on this information, would you think this is co-dominance or incomplete dominance?

TIA.

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[xucardsfan08]

My educated guess would be incomplete dominance.

 

[alleycat9]

I thought this was incomplete dominance as well ... like red/pink/white flowers. Blue being a mixture of white and black.

But Schaum's says it is co-dominance.

The ratios are the same 1:2:1 for incomplete dominance and co-dominance, so that alone cannot tell you anything.

Does incomplete dominance even occur in animals or just in plants?

Most of the examples for codominance are animals, and one is soybeans. Most of the examples for incomplete dominance are plants/vegetables/flowers.

UPDATE: Further reading from the web shows Andalusian fowl as being CO-DOMINANT or INCOMPLETELY DOMINANT, depending on your reference source.

CO-DOMINANT: The white chickens are actually splashed with black feathers, black birds are completely black, and Andalusian Blue is a mosaic of black and white feathers. So, yes, in this case, it would be co-dominant. And I think this reflects the most recent understanding of these fowl genetics.

This is analagous to roan cattle (red cattle x white cattle) which is a red/white mosaic.

INCOMPLETE DOMINANCE: Andalusian Blue is considered a new color, a mixture of "splashed" white with black. So, in this case, incomplete dominance. Most likely this reflects older, less recent understanding.

 

[alleycat9]

Just wanted to mention the following as examples.

INCOMPLETE DOMINANCE

Thallasemia or Sickle Cell Disease

Homozygotes have the worst form.
Heterozygotes have a milder form.
Homozygotes are healthy/normal.

CO-DOMINANCE

Human Blood Type
mosaic appearance, as in roan cattle (red and white)

 

[AnEyeLikeMars]

I thought this was incomplete dominance as well ... like red/pink/white flowers. Blue being a mixture of white and black.

But Schaum's says it is co-dominance.

The ratios are the same 1:2:1 for incomplete dominance and co-dominance, so that alone cannot tell you anything.

Does incomplete dominance even occur in animals or just in plants?

Most of the examples for codominance are animals, and one is soybeans. Most of the examples for incomplete dominance are plants/vegetables/flowers.

UPDATE: Further reading from the web shows Andalusian fowl as being CO-DOMINANT or INCOMPLETELY DOMINANT, depending on your reference source.

CO-DOMINANT: The white chickens are actually splashed with black feathers, black birds are completely black, and Andalusian Blue is a mosaic of black and white feathers. So, yes, in this case, it would be co-dominant. And I think this reflects the most recent understanding of these fowl genetics.

This is analagous to roan cattle (red cattle x white cattle) which is a red/white mosaic.

INCOMPLETE DOMINANCE: Andalusian Blue is considered a new color, a mixture of "splashed" white with black. So, in this case, incomplete dominance. Most likely this reflects older, less recent understanding.

I was thinking about this, and I would have said incomplete dominance as well. I was wondering though, why might Schaum think it's co-dominance. Maybe your assumption that black blended with white is blue is wrong. I guess you could say in incomplete dominance, black and white would blend to become grey. Since the phenotype is blue, this is a unique phenotype that occurs when the black and white alleles co-occur, so it's co-dominance. Just a thought.

 

[alleycat9]

Nearly all the web resources I have found use Andalusians as the quintessential example of incomplete dominance.

The only other clarification is that white may be referred to as "splashed white" b/c there is black pigment randomly distributed on the plumage (ie, it is not clustered). The color blue has also been called blue-gray, gray, or slate blue. So, I don't think it is a perception of color. I think it really is a blending of colors that you see, and not a mosaic -- black, white, black, white all over, like in roan.

So, Schaum's, perhaps not knowing much about this particular fowl genetics, may have thought this was analagous to cattle (red, roan, white)?

Schaum's is consistent, though, in the use of the Andalusian chickens as Codominance. In Chapter 9, #9.40, also describes the heterozygote as codominant.

I would still say Incomplete Dominance, based on all the extensive resources on the web.

Found way more about these chickens than intended. The original paper from Bateson describes it as "blending inheritance" and it was used as an example in the same category as snapdragons and four-o-clock flowers, both of which demonstrate incomplete dominance.