Chromosomes and Inheritance
Go to http://learn.genetics.utah.edu/content/begin/traits/ (can link from my webpage) and work
through everything on the right side of the page, under Chromosomes: The Vehicle of Heredity.
1. What is a chromosome?
When a cell is in interphase, its DNA is not visible because it is composed of extremely thin, but
long molecules. It is referred to as chromatin at this time. If the DNA from a human cell were
removed and stretched out, about how long would it be?
Chromosomes become visible when they wind around proteins called histones. Repeated
winding and coiling produces the densely wrapped structures that we call chromosomes. While
humans have 46 chromosomes, the number varies widely in other organisms. For example,
mosquito has
chromosomes, and an onion has
chromosomes, while a carp has
.
2. Close this window and go back to the main page and click on How do scientists read
chromosomes?
Each of the chromosomes in humans has been assigned an identifying number from 1-22 and X
or Y. The first 22 are present in pairs, making the cells diploid. In order to identify
chromosomes, they are typically treated with Giemsa stain which reveals characteristic patterns.
Describe the characteristics of chromosomes that are used to identify them.
Why is the centromere important?
3. Now use the distinguishing characteristics in Make a Karyotype – do it with “hints off!”
When you have completed the karyotype, identify its sex:
During what phase of mitosis do you think that the chromosomes used in the karyotype were
obtained? Explain.
4. When gametes are formed, the chromosome number must be cut in half to produce haploid
cells. This ensures that the normal diploid chromosome number for the species will be
restored when fertilization occurs. Review the events of Meiosis and Fertilization in Using
Karyotypes to predict genetic disorders. Now move on to the animations illustrating
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abnormal meiosis, and those illustrating how monosomy and trisomy would be produced.
Finally go through deletions and translocations.
How do terminal deletions differ from interstitial?
Distinguish between reciprocal and Robertsonian translocations.
Now for the quiz!
In the box, identify the outcome for each of the fertilization scenarios:
5. Are telomeres the key to aging and cancer? We discussed the role played by telomeres in
limiting the number of times a cell can divide. Review the information on DNA replication
and how telomeres protect the coding portions of DNA. You can listen to the podcast if you
want, but it’s not required. Now read the main entry on telomeres. About how many base
pairs are lost each time a cell divides?
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What enzyme maintains telomeres in sex cells and young embryos in which frequent cell
division is necessary?
Explain how cancer cells are able to become immortal.
Telomeres have also been implicated in normal aging. What other factors appear to
contribute to the decrease in effective cell functioning in aging humans?
Is it reasonable to expect that the “normal” human lifespan could continue to increase to be
hundreds of years? Explain.
6. Molecular Genealogy
Describe each of the four types of DNA found in an individual and explain how each can be
used to trace family lineage.

Autosomal

X chromosomal

Y chromosomal

Mitochondrial
What is a haplotype?
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