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Mary H.
Professor, Research scientist, Certified Teacher grades 5-12
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Biology
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Question:

The birch mouse is a small rodent that dwells in Europe and Asia. In the Caucasus Mountains scientists have captured three kinds of birch mice. They cannot be separated or distinguished based on external appearance (phenotype), but the three kinds have very different karyotypes. Their diploid chromosome numbers are 2n= 27, 2n= 42, and 2n = 50, and differences in chromosomes include many identified inversions. The birch mice live in the same general region, but their geographic distribution does not overlap. Are they different species, or do they represent populations of the same species?

Mary H.
Answer:

These mice probably represent three different species. Their very different karyotypes, or chromosomal diploid numbers are evidence that the populations are reproductively isolated, especially because there are many inversions involved. Inversions suppress recombination during crossing over, as there is a faulty "lining up" of homologous gene sequences. Even if the populations came into contact and mating occurred, the zygote my not survive or the offspring may not survive. This is an example of post-zygotic isolation. To definitively test whether the three kinds of birch mice are separate species, they should be bred to see if hybrid offspring are born and/or survive. If hybrid offspring are born, the fitness of the offspring should be evaluated. Hybrids are not expected to be captured in the wild as they have allopatric distributions.

Anatomy
TutorMe
Question:

Imagine you are walking along a sidewalk and you trip and fall. Oh, no! You have broken your lower leg. Both lower leg bone are broken straight across under the knee. One bone is jutting out through the skin. Name the kind of fracture that has occurred, and list all bones and major muscles that would be affected in the lower leg only (you do not need to include bones and muscles of the thigh and foot).

Mary H.
Answer:

This is a compound fracture, because bone is jutting out through the skin. The broken bones are the tibia (larger T-shaped bone, T for tibia), and the fibula. The fibula is always lateral to the tibia (fibuLA for lateral). The major muscles that would be torn and/or damaged include: Anterior: tibialis anterior, Lateral: peroneus longus, peroneus brevis, Posterior: gastrocnemius, soleus, popliteus

Physical Science
TutorMe
Question:

What is sublimation? Name one substance that sublimates and how this substance is useful.

Mary H.
Answer:

Sublimation occurs when a substance transitions from a solid state of matter to gaseous state of matter without first becoming a liquid. Under normal conditions, frozen water will not sublimate, as it will first melt into a liquid, then evaporate to form water vapor: ice, solid (frozen water, H2O) ---> liquid (water, H2O) ---> gas (water vapor, H2O) Dry ice, which is frozen carbon dioxide, sublimates: dry ice, solid (frozen carbon dioxide, H2O2) ---> gas (carbon dioxide gas, H2O2) Uses for dry ice (frozen carbon dioxide) include keeping food and medical supplies frozen while they are being shipped. Dry ice cools at a lower temperature, does not make the contents of the package soggy, and lasts longer than ice made from water.

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