Many genes work together to lead to the development of our body. A single gene alone, such as
Noggin, cannot create a fully functional body. Similarly, a gene that is missing or is malfunctioning can greatly alter the development of the embryo. In
Your Inner Fish, Neil Shubin explains how mutations in the genes of a fruit fly larva had a significant impact on the development of its organs when he writes, "[t]hese flies had organs in the wrong places- a leg where an antenna should have been; an extra set of wings- or were missing body segments"(Shubin, 108). Utilizing these mutants has allowed Mike Levine, bill McGinnis, and Matt Scott to recognize the presence of a homeobox.
Consider the theme of Continuity and Change.
How do mutations occur? (Refer to Unit 10: DNA, RNA, Protein Synthesis)
How are mutations essential in understanding the role of each gene sequence?
What is the significance of Hox genes that are found in various species? (Include ideas of continuity and change. What is being altered? What is kept relatively constant?)
(Keigo Tanaka; tanakarus3@hotmail.com)
The causes of mutations depend on the type of mutations that occur. Some types of mutations that we have studied include point mutations, base-pair substitutions, missense mutations, nonsense mutations, insertions, and deletions. Point mutations are caused by chromosomal rearrangement in a single base pair of a gene (Campbell 344). Base-pair substitution mutations are caused when one nucleotide ands its pair is replaced with another pair of nucleotides. Missense mutations are caused by a substitution that causes an amino acid to change into another (Campbell 345). Nonsense mutations are caused by a codon changing to a stop codon, which terminates translation early. Insertions are caused by additions of a nucleotide pairs in a gene and deletions are caused by a loss of a nucleotide pair in a gene (Campbell 345).
ReplyDeleteMutations are essential in understanding the role of each gene sequence because it allows us to see the function of each gene and what the outcome of changing the gene would be on the organism. Mutations help us to understand which genes control which traits because if there is a clear mutation, such as someone having six fingers, we are then able to identify the gene that controls the number of fingers. The significance of the Hox genes found in various species is that versions of it appear in every animal with a body. Hox genes are important because they control body plans and can cause mutations in the bodies of organisms. For example, Hox genes control proportions of the body and development of organs and limbs. The fact that Hox genes are found in every species with a body is very significant because even though there are different numbers of Hox genes found in different species, all animals with bodies have the same sequence of genes.
This is important because it demonstrates continuity in organisms over time. This is closely related to the theme of continuity and change because the Hox gene is continuous in controlling organism body plan from the earliest organisms with bodies to humans beings; change is demonstrated because the number of Hox genes has been altered for different species and has created bodies with different plans. The types of body plans, types of organs and proportions of bodies, and number of Hox genes has been altered for different organisms. In addition, the effect on the phenotype is different for each species. Sometimes a mutation will completely change a phenotype, and other times it will partially change a phenotype or have no effect at all. What is kept constant is the homeobox, which is the short sequence of DNA that can cause body plan mutations and create the organism's body plan. The continuation of Hox genes in all organisms with a body allows for genetic continuity through many generations, while the different body plans and mutations that occur allow for diversity.
Sources:
AP Biololgy- Campbell Reece
http://www.nature.com/scitable/topicpage/hox-genes-in-development-the-hox-code-41402
Marissa Lobl marissa.lobl@gmail.com
The theme of continuity and change is evident when analyzing the similarities and variations in animal bodies. The animal body is crucial to understanding evolution, for the animal body plan remains somewhat continuous throughout history as a result of Organizor, or Hox, genes. Like Marissa said, the Hox genes and genetic mutations are vital to the theme of continuity and change. By studying these genes and their mutations we can understand how certain animals were able to take advantage of mutations as well as use old parts in new ways.
ReplyDeleteAs Marissa explained, mutations are the main source of variation in evolutionary history. But just as important as the mutations are the genes that when not mutated, preserve the continuity in the animal body plan. The animal body, throughout evolutionary history, has maintained certain characteristics such as tissue development. These common characteristics are coded for in what has become known as Hox genes. According to Neil Shubin, “Hox genes appear in every animal that has a body” (Shubin, 110). It is these Hox genes that link seemingly unrelated species such as jellyfish and humans. Hox genes play many different roles in the formation of animal bodies. For one, they mold almost all animal bodies, establishing up-down and back-front axes (Shubin, 110). These genes also establish proportions, which is why you’ll rarely, if ever, find an animal whose head is larger than its body. Also, the number of Hox genes varies by species. Because more complex animals, such as mammals, tend to have more copies of Hox genes, it is likely that the genes arose from duplicates of Hox genes in earlier species. But essentially, from an evolutionary standpoint, the Hox genes are the reason as to why animal bodies have similar structural patterns. The Hox genes contain the themes of animal heads, limbs, organs, and more.
Mutations in DNA sequences account for variation in body plans. Mutations can occur in a multitude of ways: point mutations, base-pair substitutions, missense mutations, nonsense mutations, insertions, and deletions. One way in which these mutations arise is through DNA replication, specifically in meiosis. Mutations in DNA sequences directly affect the proteins produced, and thus the traits expressed. When Hox genes are altered, drastic changes may occur, such as the suppression of limb formation, as seen in experiments on insects (Campbell 527). Even more importantly, when these genes are altered as a result of meiosis in order to form gametes, the individual’s offspring may exhibit a variation or mutation that can prove to be a selective advantage (http://bio.utsa.edu/faculty/gaufo.html). For example, as earlier stated, the alleged mutation in the number of Hox genes found in different species contributed to a variation that allowed for further development of complex animals.
Marissa did not mention, however, that mutations are a powerful tool in understanding the role of DNA sequences. By altering a gene sequence and observing the chances in gene expression, scientists can determine what functions specific sequences serve. For example, Shubin described how scientists ‘breed mutants to make a whole population where every individual has the genetic error….and compare the genes of individuals with the mutation to those without”, ultimately enabling them to “pinpoint the region … responsible for the mutant effect” (Shubin 108). This experimental process has also been used in various other studies, such as the embryonic development.
Hox genes and mutations are mainly accountable for the idea of biological continuity and change. Without these key apparatuses we would not have limbs and organs, but we also would not have complex brains and sensory organs. Also, scientists can use mutations to their advantage, utilizing them to discover functions of specific genes.
Sami Kopinsky - sami_kopinsky@yahoo.com