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ETD 43 A. Draw + Explain Both: A. Cross BbEe x bbee: What pheno ratios would you expect if the genes were: 1. Unlinked 2 Linked 3. Involved Crossing Over
January 16, 2014 at 7:59am


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Sophie Wulfing
January 21, 2014 at 8:04pm

Parent, Unlinked.  Mom can only pass the recessive alleles, Dad can pass 4 different combinations:BE, Be, bE, be.  Then ratio for these parents off-spring would be 1:1:1:1.  The child that inherited Bebe & bbEe would hsvr s different Phenotype than either parent, making it a recombinant genotype.  

Linked is when two of these traits are found on the same chromosome.  Example, BE on same, vs. be on same.  Then mom could still only pass one type (be), but Dad could only pass two types, making 1:0:0:1 phenotypic ratio.  Both versions of child would be the same as one of the parents, making zero recombinant possibilities.  Running the experiment will result in 1:1:1:1 or a 1:0:0:1 ratio which will tell whether the genes are cross-overs.

Sophie- I had to review parental and recombinant types and what they mean. As for the unlinked genes, it's easy to figure out with a punnent square. The linked genes are conceptually a little harder, and I need to visualize the concept of the two genes on a chromosome, and remember that they result in a lot less variation. Crossing over can only be determined by running the experiment and comparing expected ratios to those which actually happened

Kevin Turek
January 25, 2014 at 10:13am

Parent: What I learned is that some traits are linked and in a heterozygous parent and  recessive parent mix this would make a 1:1:1:1 ratio if it was unlinked and 1:1 if it was linked. Then if there was crossing over you could see ratios that were close to 1:1 but it would not be exact.

Student: This was easier as I already had explained the idea of crossing over to my mom. I had to explain that linked meant the traits laid on the same chromosome. But then I explained how these differences led to different ratios, and that since we can predict the ratios, we will identify when there is crossing over.

Selena Clem
January 27, 2014 at 9:57pm

Parent: If genes were unlinked then the ratio would be 1:1:1:1, due to the homozygous recessive parent. If the genes were linked then the ration would be 1:1 displaying only parental types with no recombinant types. If there was crossing over then the phenotypic ratio would be close to the linked ratio, except there would be some recombinant types.

Student: If genes are unlinked they're on separate chromosomes, and thus independent assortment would occur and the ratio would be equal between parental types and recombinants. If there was linkage, meaning the genes are on the same chromosome, then there would only be parental types in the F1 generation. If crossing over occurred then their would be mostly parental types with a few recombinants due to the swapping of genes when the homologous chromosomes were joined at the synapse and crossed over at the chiasmata.

Madison Boggan
January 14, 2015 at 4:32pm

Parent: Unlinked genes-on separate chromosomes     Ratio: 1:1:1:1 because they can assort independently

Linked-on same chromosome     Ratio: 1:1:0:0  because there are no recombinations 

Crossing over-occurs in meiosis and the genes must be linked   Ratio: something different, the amount of each parental type will be higher than the two recombinants. 


Student: This was a hard one to explain as it is a complex, unseen concept. To explain linked and unlinked genes, I said that unlinked genes are similar to two clouds freely floating around. On the other hand, linked genes are like clouds at the end of a rainbow (in a drawing) because they often travel together. I told my mom that crossing over is like the clouds at the end of the rainbow switching around with pots of gold. 


Talesh Patel
January 25, 2015 at 1:28pm

Parent: first Talesh had to explain that Genotype is a gene that is expressed(passed down).  Then he drew a matrix of crossing BbEe with bbee.  He explained the BE would be a parental type of the father. Be and bE would be recombinent  and look like both parents.  be would look like the mother.  Unlinked  - the ratio would be 1:1:1:1     Linked in chromosomes, the ratio is 1:0:0:1 because the mother only has one genotype.  Crossing over happens when both Genotypes are on the same chromosomes and they cross an create a recombinant percentage that varies depending on how many map units they are apart.

Talesh: This was hard to explain to my mom as she didn't really understand genotypes and phenotypes. I started by explaining the unlinked genes and how they are on separate chromosomes, so they mix at a ratio of 1:1:1:1 and can either be a mixture, or look like one of the parents. Then we moved onto linked where the genes are on the same chromosome. Because they are the same for the female, the only potential offspring are all parental types with a ratio of 1:0:0:1. When crossing over, both genes happen to be on the chromosome and depending on how many map units they are away, they will cross over and provide a recombinant type percentage. This was a tough concept to grasp entirely but the ratios are easy to remember.

Chloe Hobson
January 25, 2015 at 6:49pm

Student: Showing my mom the pictures of each parent and what the offspring would look like helped explain the ratios. I drew a chromosome to explain the concept of linked genes. Linked genes are like two people holding hands and travelling together. When two people hold hands and stand very close, it is harder to break them apart (think red rover) than when they stand far apart. This helped me explain why crossing over has a bigger effect on linked genes that are further apart

Parent: Unlinked would be 1:1:1:1 (independent assortment)

linked would be 1:1:0:0 because genes travel together

Crossing over has another ratio..will have more parental types than recombinant types

Seeing pictures and listening to the analogy Chloe made about crossing over helped make the concept much  more understandable


Supreet Sandhu
January 21, 2018 at 2:47pm


I gave my dad some context to the question by drawing pictures of some phenotypes and then showing those phenotypes on a chromosome. It was a bit hard of finding a starting point to explain the question from. But I started by just defining some simple vocab and then i used a punnet square to showcase different phenotype ratios.It was a bit hard to explain crossing over so I used an analogy of two friends holding hands to explain crossing over. I had to use the book to find real world examples of linked and unlinked genes.

parent: Linked genes are close to each other on the chromosome and move together when new genetic DNA is made. Unlinked genes are usually further apart on a chromosome and do not move together. If the genes are unlinked then the ratio in the offspring should be 1;1:1:1 and if it is not that ratio then the genes are linked and on the same chromosome. You need two genes to have them be linked and gender can be one of those genes.

Kaelynn Leick
January 23, 2018 at 9:45pm

Parent: Tonight I learned about the basic function of DNA replication, how it is like cloning a strand of DNA. I learned that Helicase unzips the double helix and the SSBP keeps the helix open. There are leading and lagging strands which is how the DNA is replicated. 

Student: I originally asked my parents what they thought DNA replication was. They both said they thought it was almost like cloning a strand of DNA. I then explained to them the different components of DNA replication, Helicase unzips the helix (dirty helicase). Single Strand Binding Proteins keep the double helix open. Toposimoeara stabilizes the double helix before the helicase unzips. Primase all down RNA primers. DNA poly III lays down DNA nucleotide from 5' to 3'. DNA poly I replaces RNA primers with DNA from 5' to 3'. Lastly, DNA ligase links together Okazaki fragments on the lagging strand.

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