Chapter Discussions
Chapter discussions are meant for you to exchange ideas and opinions with your fellow classmates on topics in the chapters that reflect contemporary and important concepts.
All exchanges in the discussions should be cordial and respectful. It is okay to disagree with someone but be respectful in your responses and support your ideas with facts when called for.
Citation: If you need to cite a particular reference you do not need to follow a particular style. Just make sure that others can find the resource by using the citation you have provided.
Instructions:
Read the information below regarding the topic for this chapter.
Answer and/or respond to the questions and topics below in a new discussion thread. This will be your “initial post”.
Your initial posting should reflect your thought on the subject and be thorough. Use complete sentences and refrain from slang. Responses should be a minimum of 2 paragraphs.
Respond to at least 2 other posts on the discussion forums.
Your responses to other students should be thoughtful and respectful. Refrain from short responses like “good job” or “I liked your post”. Instead follow that up with why it was a “good job” or why you liked it.
Chapter 8 Discussion
There used to be the assumption that the complexity of an organism should be reflected in how much DNA it has and therefore how many chromosomes they have. However, a tour through plants and animals demonstrates that this is simply not the case. Onions have 5X as much DNA as humans and many insects have over a hundred chromosomes.
This is an interesting phenomenon and for this chapter you are going to go in search of an answer to the question “Why do organisms have different numbers of chromosomes”.
For this discussion you should search the internet on this question, educate yourself on this question, create a discussion reflecting on what you think the explanation is for this question. There are many different explanations possible but in your write up you should have the following details:
Your explanation of why organisms have different numbers of chromosomes.
Some evidence to back up your explanation.
A citation of your source (a link to the webpage where you got your ideas is fine.).
Initial Post
Respond to the questions above in a new thread in the discussion forum.
Respond to 2 other posts
Respond to two other student posts reflecting on their responses. Did you agree or disagree? Why? Was it something you had considered? Is there maybe something they should consider?
Post 1:According to Sci Show, “mistakes happen.” Related to chromosomes, specifically. When unpacking the question of why organisms have different numbers of chromosomes, the video suggests a few options. First, damage can occur and leave pieces of the chromosome off during replication. Random fusion is also discussed as a source of decrease in chromosome number of an organism.
The video also addresses why certain organisms end up with much more chromosomes than others, such as the example of the Adder’s Tongue plant with 1260 chromosomes. The theory of why this organism has accumulated so many chromosomes over its very long existence is from nondisjunction during Meiosis. What’s not addressed in this video is why there is such a huge discrepancy in organism chromosomal counts. Why there some variants of goldfish, seemingly less complex, that have 104 while humans, seemingly more complex, have 46?
Post 2:
in a typical human, there are 23 pairs of chromosomes, where we inherit 23 chromosomes from our mom and 23 from our dad. The sperm and egg are both haploid which results in diploid zygote, a fertilized egg. You would think that all living things would also have 46 chromosomes, but this is not true. Different organisms have different amounts of chromosomes. According to Konstantinovsky’s article regarding chromosomes, frogs have 26 chromosomes and shrimp have 508 chromosomes. This means that frogs inherit 13 chromosomes and shrimp inherit 254 chromosomes from each parent. These two speices are also diploid like humans.
So why do humans have 23 chromosomes? According to the same article, Dr. Belen Hurle states humans have 23 chromosomes due to evolution. Reading the article from PBS, it states that apes have 48 chromosomes which is two less than humans. Dr. Hurle was stated that they believe the two chromosomes fused together creating chromosome 2 which is for humans. They further explain that this why apes and humans have similiar genomes. Reading the PBS article they further state that apes have a split chromosomes. This supports the reason why humans have 23 pairs of chromosomes while apes have 24 pairs.
