Assignment 2 – Animal Behaviors
Part 1: Write about 100-150 words below the questions
Question: if you, or someone you know, holds
any of these misconceptions about
genetics. If so, describe both the misconception and the correction.
Alternatively, you can write about any questions you have about genetics,
such as these questions. If another
student posts a question that you can answer, please do.
Although I’m asking you to write about
what you have learned and what you have found confusing, I want you to
avoid repeating what others have written. You are welcome to build on posts by
adding additional information or an opposing view. Remember, we’re trying to
simulate the dynamics of classroom discussion.
Write about 100-150 words above the questions
Part 2: Answer those MC questions and checkpoint questions
- To
understand animal behavior, it is helpful to have
an understanding of genetics. Genetics is a complicated topic,
and I don’t want to get bogged down in the details. Below, I’ve
listed the key concepts for this course, and highlighted the key
terms in red. I hope some of these concepts are familiar, but,
if not, don’t try to memorize this list. Just read through it and watch
some of the videos below. Later, if you think you’re missing
something, you may want to revisit this list for clarification.
- Living things have the potential to reproduce themselves. The instructions for this reproduction are contained within the living things’ DNA (also known as its genome).
- DNA is a very long molecule built from just four different components, which are identified by the initials “A”, “T”, “C”, and “G”. In all, there are about 3,000,000,000 components in human DNA.
- DNA contains the instructions for making proteins. Proteins do the work of assembling, maintaining, and coordinating cells in the body.
- The instructions for making one protein are called a gene. The particular sequence of A, T, C and G in the gene specify the components of the protein.
- Most organisms have two copies of each gene, one copy from mom, the other from dad. These copies are often identical. When the copies differ, each variant is called an allele.
- In addition to the instructions for making proteins, DNA contains instructions about the instructions. For example, some parts of the DNA indicate where a particular gene starts and where it ends.
- Whether and how often a gene is used to make its corresponding protein, that is, how often a gene is expressed, depends on many factors, including the activity of other genes and signals from the environment.
- The signals that control gene expression may originate in the local cell environment or in the external environment. For example, the local environment in the pancreas promotes the expression of the insulin gene. The insulin gene is present in all parts of the body, but it is only expressed in the pancreas. As another example, the diet fed to a bee larva controls the gene activity that determines whether the larva will develop into a queen bee or a worker bee.
- The way the environment interacts with the genome is through chemicals that attach to DNA and regulate gene expression. The chemicals that alter the genome are called the epigenome. Some aspects of the epigenome can be inherited.
- It is meaningless to ask whether a trait is controlled by genes or by the environment because gene expression is always affected by the environment and because the proteins created by genes alter the environment. So, every trait is always the result of interactions between the gene and the environment.
- It does make sense to ask whether individual differences are due to differences in their genes or due to differences in their environment (or to both). For example, if two sparrows sing different songs, it is reasonable to ask whether this difference is due to a difference in their genes or to a difference in their environment. But each sparrow is able to sing because of a gene/environment interaction.
- The genome (DNA) of an individual is its genotype. The traits of the individual are its phenotype. (Traits are observable characteristics – things like hair color, blood type, height.) There is not a simple relationship between an organism’s genotype and its phenotype. Rarely does one gene directly determine one trait. Instead, one gene may contribute to multiple traits, and one trait is related to multiple genes. Also, because gene expression is always regulated by the environment, the same genotype can produce different phenotypes in different environments.
For more background, watch any of these excellent videos: NOVA Scientific American ,
CA
academy of sciences, and/or visit this site.
(If this material is familiar, you can skip the videos. But if the material is
new to you, I recommend watching at least a couple of the videos.)
Now that we’ve had this refresher, we can get a deeper appreciation for why adaptations aren’t always perfect solutions. Here’s a particularly interesting example:
sickle cell anemia
What is the relationship between sickle cell anemia and malaria?
Top of Form
1 : Malaria increases the chance of the mutation that causes sickle cell anemia
2 : Sickle cell offers protection against malaria
3 : They both occur in the same regions of the world, but that is just a coincidence.
Bottom of Form
Sometimes mistakes are made when DNA is copied from one generation to the next. These mistakes are called mutations and on average each of us has
Top of Form
1 : a 1 in 50 chance of having a mutation
2 : on average 4 million mutations
3 : about 40-50 mutations
Bottom of Form
Individuals with two different alleles for a particular gene are said to be
Top of Form
1 : homozygous
2 : heterozygous
3 : homogeneous
4 : heterogeneous
Bottom of Form
- And here’s another trait that can be directly linked to genetic differences that reflect adaptations to different environments: lactose intolerance
Lactase is
Top of Form
1 : an enzyme that breaks lactose, the sugar in milk, into smaller molecules that can pass the stomach wall.
2 : present in all adult mammals
3 : a protein that gives milk its white color
Bottom of Form
The difference between individuals who are lactase persistent and individuals who are not is related to
Top of Form
1 : the gene that specifies lactase
2 : a mutation that affects the expression of the lactase gene
3 : the anatomy of the stomach
Bottom of Form
How many DNA components (A, T, C and G) differ between people who are lactose intolerant and those who are lactose tolerant?
Top of Form
1 : 1
2 : 5
3 : 10
4 : 50
Bottom of Form
- Sickle cell anemia and lactose intolerance are directly related to a single change in the genetic code. That makes these traits both good and bad examples for this course. They’re good examples because they clearly demonstrate the relationship between mutations, natural selection, and evolution. But they’re bad examples because they may give the impression that there is often a direct relationship between a gene and a trait. This direct relationship is exceedingly rare. Almost always, multiple genes are involved in a trait. Moreover, traits are almost always determined by a complex interaction between the genes and the environment. This complex interaction is a point I want to emphasize, so let’s end with a video that explains part of the mechanism involved in this interaction: the epigenome. (Here’s another short video on the topic.) You may find information in this video helpful for the final discussion.
- Want to learn more? The videos
above are classic examples of physical traits that have a clear
relationship to single genes. If you’d like an example of a behavioral
trait with a relationship to a gene (actually two genes), Check
out this article about how the same gene variation
may explain both the hypersociability of dogs and of humans
with Williams-Beuren syndrome (or go directly
to the source).
Checkpoint Question
If every cell in the human body has the same genotype, why don’t they all have the same phenotype? (Why are muscle cells different from skin cells?)
Part 3: Write a 200-250 words short essay below the questions
You may have heard that some scientists are working to “de-extinct” the
woolly mammoth. The scientists recovered fragments of mammoth
DNA from frozen animals, and they plan to use elephant DNA to fill in any
missing segments. The scientists plan to insert this DNA into the egg of an
elephant, which they will implant in an elephant, who, if all goes well, will
give birth to a mammoth. Aside from the obvious limitation of using some
elephant DNA, do you think these de-extincted animals will be woolly mammoths?
The idea of de-extinction is sometimes promoted as a way to deal with the rapid
extinction of animal species due to human activity. What are the pros and cons
of this plan? Here are some references (please watch/read at least one before
you join the discussion):
BBC earth
Forbes
PBS: It’s Okay to be Smart
The Field Museum of Natural History
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