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ETD 41 A. How could 2 brown eyed parents produce a pale blue eyed and then a bright green eyed child? B. What are the genotypes of the 2 parents and the 2 children?
January 16, 2014 at 7:57am


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Sophie Wulfing
January 21, 2014 at 7:27pm

Parent:  Brown eye gene is dominant.  Blue is recessive.  Phenotype is trait that's expressed.  Genotype is the genetic makeup.  Assuming both parents have 1 BRN & 1 BLU allele, Blue eyed child is 0.25.  Phenotypic ratio is 3:1.  If one parent is 1 BRN & 1 BLU, and the other parent is Blue eyed (i.e. 2 BLU alleles.), then probability of Blue eyed child is 0.5; ratio is 2:2.  

Enter the green eye; epistasis is where one gene stands on another gene, which is saying that more than one gene of each parent codes for eye color, therefore, different genes, one could code for a green eye.  In the absence of a brown (dominant) allele, green allele can blend, if both alleles are green, then dark green eyes.  If 1GRN & 1 BLU allele, then bright green.  Incomplete dominance or blending.

Sophie- This initially was a complicated concept for me, but after reviewing, I just have to remember that the genes that code for eye color are polygenic, meaning more than one gene decides. Also, Brown eyes are most dominant, and after that, the green has incomplete dominance over blue and they experience blending as a result

Kevin Turek
January 25, 2014 at 9:43am

Parent: What I learned from this is that dominant and recessive genes don't always work as simply as they usually do. There is sometimes blending and incomplete dominance. While brown is dominant so is green. Then blue eyes is a recessive. The parents would have to be heterozygous then there would be a 3:1 ratio of a brown eyed to blue eyed. The kid would have to be pure bred blue recessive.

Student: Another really hard concept. First I had to review what the difference between dominant and recessive was then immediately tell her that it doesn't always work this simply. I had to explain that sometimes blending or incomplete dominance can occur creating weird outcomes. I still don't think either of us grasps this concept 100 percent yet so this would be a good thing to study.

Selena Clem
January 27, 2014 at 9:28pm

Parent: Since eye color is a polygenic trait, meaning that many genes control it, both pale blue and bright green eyes can be found in the offspring. Assuming at least one of the parents are heterozygous they can produce dark green-eyed, bright green-eyed, and pale blue-eyed children due to incomplete dominance, which causes a blend of the dark green and pale blue traits, making bright green. The possible genotypes of the parents would be BbGb and Bbbb, while the children could be Gbbb and bbbb

Student:Two genes that control eye color are Herc 2 ( brown vs blue) and Gey (green vs blue). The cross of the brown eyed parents and the condition of incomplete dominance in the genes causes the traits of bright green and pale blue to become expressed in the F1 generation which have the genotypes Gbbb (bright green) and bbbb (pale blue)

Madison Boggan
January 08, 2015 at 5:10pm

Parent: A child could have blue eyes from two brown eyed parents because blue eyes are a recessive trait and the parents could have had brown eyes (dominant) but also had a recessive gene as well. The child could have gotten this piece from each parent. As for the child with green eyes, this is due to epistasis which is one gene "standing upon" the other and controlling it. Eye color is determined from many different genes. 

Parent: Bb Gb and Bbbb or BbGb

Blue child: bb bb

Green child: bbGb

Student: While explaining this genetic concept to my mom, I came up with an analogy. I told her that this was similar to an ice cream cone. It is possible to have two different flavors of ice cream but sometimes one is more strong or powerful (dominant) than the other. Also, you can buy ice cream and put it on the same cone (genetic code for a person) at multiple stores (multiple places on a gene). You then have an ice cream cone (code) with epistasis going on.

Mary Fuller
January 22, 2015 at 9:20pm

Student: In order for this to happen, both parents must be heterozygous. Also, epistasis must occur, meaning that genes “stand upon” other genes, controlling the expression of other genes. The possible genotypes of the parents could be BbGb x Bbbb or BbGb. The pale blue eyed child is produced when the child inherits the bb genotype. The bright green gene however, comes as a result of the epistasis. Bright green eyes are a result of the green gene and a blue gene. For both cases, the child could not inherit an allele for brown eyes because brown eyes are dominant and so the child would have brown eyes if that were to occur.


Parent: This was a very confusing concept for Mary to explain to me, however Punnett squares helped both of us to understand. She explained that eye colors are determined by many genes and therefore, it is not just a single gene that matters. Eye color is polygenetic.

Amanda Troxel
January 25, 2015 at 10:52am

Student: I explained to my mom what the difference between the dominant trait and the recessive trait are and also phenotype versus genotype.Then I told of how the child is able to have blue or green eyes from two brown eyed parents due to the parents having the dominant brown eyed trait and the recessive blue eyed trait. This would mean that one of the parents would be heterozygous to produce dark and light green eyes and pale blue eyes. Through Mendel's experiments with pea plants, he found out that there can be incomplete dominance where the traits are blended, causing the different shades to appear. Phenotypes for the parents are either Bbbb or BbGb. The pale blue child's phenotype is bbbb and the bright green would be Gbbb.

Parent: Amanda described the different meanings to all of the genetic terminology so that I would be able to understand the specific differences between each of them. She then went on to explain what the P, F1 and F2 generations are and how through incomplete dominance the genes could be blended causing the different color shades to appear. Amanda also showed me the example of the pea plants where the white and red parent flowers produced a pink baby. In this example I learned that the brown eyed trait is dominant even though the parents also could be carrying the recessive blue color. So the child would have gotten the recessive genes to produce the different colors.

Sara Wilton
January 18, 2016 at 12:20pm

Parent: I learned that more than one Gene determines eye color, and that there are lots of combinations that happen - Brown would be most common, Green would be next common as it is can mix with the blue. Pale blue  has fewer chances to be expressed. I never knew why my eyes looked green in some light, and blue in others!

Student: Explaining the difference between complete dominance and incomplete dominance was a little tricky. We started at the beginning where I drew a chromosome and identified a locus. From here, I explained the difference between the phenotype of a person and the genotype. We used the same eye examples from the ETD, and we practiced drawing the punnet squares together. This solidified my understanding about the difference between codominant and dominant genes. 

Anne Sweeney
January 20, 2016 at 9:04pm

Parent: Anne explained all the vocabulary first and wrote out the genotypes. I learned that two brown eyed parents could produce a blue eyed child since it’s gene is a recessive trait that can be present and green eyes are produced when one genes stands upon another gene controlling it (epistasis). Eye color is a polygenic trait which means it has more than one gene controlling it. I also thought it was interesting that anyone with blue eye has no/ a lack of  pigments.

Student: It was useful to go over the vocabulary in the beginning so by the time I explained the process my mom was familiar with the concepts. It was also helpful to review the difference between incomplete dominance and codominance. I used analogies when I explained each, complete dominance is like a mix of ingredients and codominance is like two players fighting. It was also useful to draw out the punnett squares for the practice of crossing genes.

January 21, 2018 at 2:31pm


I first asked my parent what he though about the question. My dad had a basic understanding of the question. I used his basic understanding and built off his thinking to create a more in-depth answer. It was useful to define some of the terms I used to explain the process first and then explain the reason why. Furthermore, i drew a punnet square to show different possibilities of the genotype to show why different genotypes would not work.

Parent:Imagine 2 parents with the genes Rr which gets expressed as brown eyes. Mixing Rr with Rr  results in - RR, Rr, rR, and rr. let us say RR, rR, and Rr express as brown eyes and rr(the non-dominant genes) express as green eyes. Sometimes when rr is passed on both genes may end up on the same DNA stand such that maybe another gene also present on BOTH DNA strands may be able to get expressed as the color for eyes such as pale blue


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