BIOL 112 Lecture Notes - Lecture 22: Dicer, Caat Box, Zygosity

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All cells in your body share the same alleles of the same genes they have the same genes because they were generated from a single cell by mitosis. Cells appear different because different types of cells express different genes (ex. blood cells make hemoglobin which makes them red) Of course, there are genes that all cells must express that are necessary for basic functions of metabolism, transcription, etc. There are also genes that must be expressed to make a liver cell a liver cell. Also genes that are only turned on in response to specific conditions, which can be tissue specific or shared by most or all cells. At transcription, transport out of the nucleus, mrna: these are all used by some organism somewhere for some gene product, but the main way of determining cell type is regulation of transcription.

Related Questions

Question 11 pts

What is a mutation?

A dangerous alteration in the genes of a living organism.

Any change in the base sequence of an organism's DNA.

Any genetic alteration in an organisms physical appearance.

A broken piece of a DNA molecule.

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Question 21 pts

How many "genetic words" are there in the genetic code formed by combining three DNA bases together?

128

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Question 31 pts

What is the shape of a DNA molecule?

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Question 41 pts

Which of the following is not one of the DNA bases used by living organisms on Earth?

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Question 51 pts

What is the genome of an organism?

The longest of its DNA molecules.

The complete sequence of DNA bases in all its DNA.

The noncoding parts of the DNA.

All the genes in an organism's DNA.

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Question 61 pts

The process by which DNA is copied to be passed on to the next generation of an organism is called:

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Question 71 pts

If every cell in your body has exactly the same DNA, why are brain cells different from muscle cells?

Because they are located in different parts of your body.

Because different types of cells use different pieces of the same DNA.

Because the noncoding DNA behaves differently in different cell types.

Because while all cells in your body may have the same DNA, they have different genomes.

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Question 81 pts

Which kind of extreme environment are psychrophiles able to survive?

Extremely low pressure.

Extreme heat.

Extreme cold.

Extreme acidity.

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Question 91 pts

What are thermophiles ?

Organisms that live in extremely cold conditions.

Organisms that live in extremely hot conditions.

Organisms that live in extremely acidic conditions.

Organisms that can live in highly radioactive environments.

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Question 101 pts

What characteristic is the bacterial species Deinococcus Radiodurans known for?

For being discovered on radio antennas.

For being able to survive high doses of radiation.

For being able to live inside rocks.

For being the first life discovered on Mars.

Ploidy refers to the number of complete sets of chromosomes (genes) present in a cell. The number of chromosomes in a complete set is a fixed characteristic of a species. Humans are diploid with two sets of 23 chromosomes. Fruit flies are diploid with two sets of 4 chromosomes. Sexually reproducing organisms are diploid, each somatic cell of an organism has two complete sets ("di" is a prefix indicating 2.). To complete a life cycle and reproduce new members of a species, mating is required. Mating brings a donation from a male and a donation from a female together. However, if the male and female cells remain diploid, the fertilization will result in a tetraploid zygote. In general, these are not viable. A mechanism is needed to form special haploid cells, gametes. The diploid set is split precisely into two complete haploid sets. That mechanism is meiosis.

The complete set of chromosomes of a species is also the complete set of genes of a species, the genome. (Yes, there is a minor contribution from mitochondria and chloroplasts. Inheritance of this information is "cytoplasmic".)

Please answer the following questions:

1. How many chromosomes in a brain cell of a fruit fly? How many chromosomes are in a liver cell of a human? Explain both answers.

2. How many chromosomes are in a fruit fly unfertilized egg? How many chromosomes are in a human egg? Explain both answers.

3. Why is meiosis necessary for sexually reproducing organisms? How many chromosomes are in a human zygote? Relate the two answers.

4. What is a gene allele? Suppose there is a gene called "bingo" and it is present once in a complete haploid set. How many alleles of "bingo" does a diploid individual have? How many copies or versions of the gene "bingo" are present in a diploid individual?

5. Modern DNA sequencing clearly identifies alleles by showing the different DNA sequence of each allele. These alleles may be termed structural alleles (I coined the term for this problem.). Classical genetics only dealt with phenotypes or visible traits. As a result, alleles of genes were identified by functionality, usually normal or non-functional. Using your knowledge of gene structure and gene expression, postulate a relationship between structural alleles and functional alleles. (include relative amounts; more, less, or equal).

Tasmanian devils (Sarcophilus harrisii), the worldâs largest carnivorous marsupials, are facing extinction. Not from hunting, or habitat loss, but from within; a transmissible cancerous derivative of Schwann cells, responsible for devil facial tumour disease (DFTD). First seen in 1996, the disease has spread widely though the population, and is now estimated to be present in 80% of the population. With the grim prognosis of ~100% mortality in 12-18 months, animals that once went through multiple breeding cycles are now lucky to reproduce once before death, resulting in a 70% decline in their population over the past decade. The cancer is transmitted by biting (a common ritual used by these animals to establish and maintain social position), with cancer cells from one animal (the biter) being implanted in the wound inflicted on the other animal. Equally common in both sexes, the disease itself is more prevalent in animals higher on the social scale, presumably reflecting higher levels of social interaction (biting). The cancer is usually first evident as facial tumors, from which metastasis to cervical lymph nodes occurs, often followed by dissemination to other organ systems. Cause of death is by organ failure or by malnutrition in those with facial tumors large enough to prevent feeding. Based on what we have covered regarding the Major Histocompatibility Complex, you would expect the passage of a cancer from one individual to another* to be a rare event (to see just how rare, read the accompanying popular press piece from the New York Times). Here are some things that you already know: *Yes, some viruses can cause cancer (example: Hepatitis B virus and liver cancer), and you can transmit a virus from one individual to another; but that is not the same thing as passing the cancer itself. v Almost all nucleated cells express high levels of class I MHC proteins on their surface. v Class I MHC proteins collect peptides produced from endogenous proteins and display them at the cell surface. v Different Class I MHC proteins bind and display different peptides. v Developing cytotoxic T-cells that recognize self-antigens are eliminated. v Mature cytotoxic T-cells conduct surveillance by scanning the peptides displayed by class I MHC proteins. v Mature cytotoxic T-cells that recognize an antigen on a cell will kill that cell (recall that cytotoxic T cell activity is important in rejection of tissue transplants).

Before the questions:
v Tasmanian Devils are not immunosuppressed.
v Tasmanian Devil cytotoxic T-cells are not broken, they can kill cells.
So neither of those should be part of your answers.
This is an ongoing research topic with large gaps in our knowledge; we really donât fully understand how this works
and so there is no âcorrectâ answer. Your job is to provide a logical argument, with some research and details to
support your contention. Note that in questions 1 & 2 class I MHC should be part of your answer, but not in
question 3.

Questions:
1.) Acquiring DFTD is basically like receiving a transplant that is not rejected. How can that be? Suggest a possible
way this could occur. Be sure to explain why you think this would work, and then explain how you would test
that model to determine if it were correct. (10 point question).
2.) Canine Transmissible Venereal Tumor (CTVT) is the other know transmissible cancer in mammals. Unlike
DFTD, CTVT does not usually result in death. Do a little research on this disease and summarize how it is
different from DFTD. Provide an explanation as to why one is lethal and the other is generally not. (10 point
question).
3.) Recently, researchers at Washington State University determined that some Tasmanian devils had developed
resistance to this cancer. By scanning partial genome sequences of resistant and susceptible animals (a
complete devil genome has yet to be assembled) they identified a set of genes where mutations appeared to
enhance resistance. Speculate as to the function of the proteins these genes encode, and explain why that
might provide for resistance (note: they were NOT MHC genes).

Mainly need guidance/ideas for #1's 1 and 3!

BIOL 112 Lecture Notes - Lecture 22: Dicer, Caat Box, Zygosity

BIOL 112 Full Course Notes

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