Incomplete and Codominance

Learning Target

• Develop a model to show how reproduction results in offspring with genetic variation.

Success Criteria

• Explore inheritance of two dominant traits.
• Use Punnett squares to model the inheritance of two dominant traits and predict probabilities of each offspring’s allele combination.
• Use two Punnett squares to model each trait independently, then multiply the probabilities to find the probability of a given allele combination.

Questions to Ponder

• Why do some alleles not fit the pattern of the standard Punnett Square?

If Gregor Mendel was right about inheritance...

...why do we have:

COLOR MIXING LAB

Materials:

• Data Table (see below)
• 4 test tubes
• masking tape
• blue and red colored water

DIRECTIONS:

1. Label each of the test tubes with the following:
   • #1 - Bl
   • #2 - UE
   • #3 - R
   • #4- ED
2. Fill two of your test tubes halfway with blue water and 2 with red water.
3. Make a hypothesis on the left side of the chart below as to what color you will get when you mix.
4. Take your “BL” test tube and pour about half into the “UE” test tube. Record the color on the right side of the chart above.
5. Take your “R” test tube and pour about half into the “ED” test tube. Record the color on the right side of the chart above.
6. Take your “BL” test tube and pour the remaining liquid into the “R” test tube. Record the color on the right side of the chart above.
7. Was your hypothesis for each color mixture correct? Provide an explanation of why you think you got each color result.

Back to Teams...

• If you compared the different samples of water to genes which one would you say is dominant and which would be recessive?

Lesson 7 Reading One: Which Instructions Get Followed?

• Read pages 83-84 in the Why Do Organisms Look the Way They Do? text.
• Read the first time by yourself.

As you can see, Ava, the girl on the right, has fair skin, bright blue eyes and blonde hair. Maria, on the other hand, has much darker skin, deep brown eyes and bouncy, black ringlets atop her head. Understandably, they have left a few jaws hanging when they popped out, and people rarely believe they are twins. So, what’s the science between this pair?

The girl's mother and father are both products of a biracial relationship, themselves having a black parent and a white parent . You’ve probably worked out by now that these girls cannot be identical twins . Those occur when a single sperm fertilizes an egg that subsequently splits into two genetically identical, but separate embryos. Non-identical, or fraternal, twins, on the other hand, are usually the result of the mother releasing two eggs at the same time, both of which become fertilized by two different sperms. Rather than being genetically identical, these share 50% of their DNA like normal siblings do.

What happened with these girls is that, thanks to the parents carrying genes for both black and white skin, Ava ended up inheriting the genes for white skin, whereas Maria inherited the genes for black skin. Such dramatic genetics are unusual, but possible. Most of the time, children will inherit a "blend" of their parents features - as was the case with their siblings. In the twins case, they each happened to inherit incredibly different features.

Back to Teams...

• Can you describe any other examples of incomplete or codominance that you have seen in your own life?