Compendium Review II: let's dig the duplication

I. Chromosomal Inheritance

A. Chromosomes and the cell cycle

B. Mitosis and meiosis
1. Mitosis
2. Meiosis
3. Comparison

C. Chromosome Inheritance

II. DNA

A. DNA/RNA: Structure and function?

B. Gene Expression

C. Genomics

D. DNA technology

III. Cancer

A. Cancer cells

B. Cancer causes

C. Diagnosis

D. Treatment


IV. Patterns of Inheritance

A. Genotype vs. phenotype

B. One and two-trait inheritance

C.When it's more than that

D. Sex-linked inheritance


I. Chromosomal Inheritance

A. Chromosomes and the Cell Cycle

Every human has 46 Chromosomes. They are paired into twenty three bonded pairs. Only the sex chromosome determines gender. In females there are two "homologous" (look alikes)X chromosomes. Males have an Xchromosome and a Y chromosome. The two separate parts of a chromosome are called "sister chromatids." One is, basically, a duplicate of the other. They are held together by a weak hydrogen bond. This holding point is called the "centromere."
Interphase is the process in which a cell grows and prepares for division. This is also when a cell goes about its specific business. In humans about 90% of a cell's life is spent in interphase. There are three stage
A microscopic view of the

Male "X,Y" chromosomes.
B. Mitosis and meiosis

1. Mitosis

We briefly touched on Mitosis above. But what exactly is it and how does it work? Mitosis is simply division by duplication. The interpahse of a cell readied everything for duplication. Chromatin in the nucleus became dense as it was produced. This is when chromosomes become visible. The Chromosomes are duplicated which make the sister chromatids. When mitosis begins the centromeres divide (it is a weak bond.) The centrosome also duplicates. The centrosome is, naturally, at the center of the cell. It contains to centrioles. This centrosomes assembles fibers that attache to the chromatids and separates them. This happens during "anaphase", the third phase of cell division. The two that precede it are the prophase and metaphase. The final phase is telophase. In prophase The centrosomes duplicate as well as the chromosomes. The nuclear envelope disappears as the centrosomes begin to move to opposite sides. In metaphase the spindle fibers of the centrosomes attach to the centromeres of the chromatids and the centromeres become aligned in the middle. Anaphase is marked by the pulling apart of the chromatids to opposite sides of the cell. Equal numbers of chromosomes are taken to each side. Telophase shows the reappearance of nuclear envelopes as the daughter cells become visible. Chromosomes become chromatin again. All the while the organelles have moved and the middle of the cell has become pinched as it becomes two cells. This is the process of cytokinesis spoke of earlier.

2. Meiosis

We now that Mitosis is duplication division. Meiosis is reduction division. The parents cell has the diploid number of chromosomes. The chrmosomes duplicate. Then the first stage of meiosis takes place.This is the last time that paired chromosomes are together during meiosis. The cell splits in two and each cell takes one of each pair of chromosomes. This cell is now a "haploid" which means it has only half the number of chromosomes. THen the second stage of meiosis, or meiosisII, takes place. Here, the centromeres holding the chromatids together, separates. The new daughter cells of each original daughter cells, now have one chromatid each. So what started as one cell has now become four with only half the original number of chromosomes. The cells that reproduce through meiosis are gametes, or sex cells. The only way that the fulll number of chromosomes will be restored is through fertilization.

3. Comparison

Mitosis and meiosis are different in many different ways. Here are some of them:

1. Mitosis consists of one division. Meiosis has two.

2. There are four daughter cells as a result of meiosis. There are only two daughter cells in Mitosis.

3. Meiosis' daughter cells are haploids, with only half of the full number of chromosomes. Mitosis' cells are diploids with the full number of cells.

4. Mitosis' daughter cells are identical to the parent cell. Meiosis' daughter cells are not.

5. During the prophase of meiosis chromosomes cross over and exchange genetic information. This doesn't happen in mitosis.

6. Pairs of homologous chromosomes align at the "equator" of the cell during meiosis I. There is only one of each chromosome that aligns in mitosis.

7. Meiosis II and mitosis are very similar except the daughter cells of meiosis are haploids.

C. Chromosomal inheritance

Humans generally have 23 pairs of chromosomes. 22 of them are autosomes (not sex chromsomes) and 1 pair is sex chromosomes. Some people end up having irregular numbers f chromosomes because of nondisjunction (non separation of chromosomes) during meiosis. This can happen at either stage. It leaves one cell with too many chromosomes and the other with too little. When a cell with too many chromosomes is fertilized it is called trisonomy. When the opposite occurs it is called monosomy. The chances of survival for one with a trisonomy is greater than that of a monosomy. Also the chance is greater if nondisjunction has occured with the sex cells. Though the "disorders" are different the extra X or Y chromosomes have littler impact on survival. Down Syndrome is the result of having one too many chromosome 21s. Turner Syndrome is the result of having only the X sex chromosome, while Klinefelter Syndrome is the result of having an exta X chromosome. Sometimes a change in the structure of chromosomes will also cause mutations. If the broken ends don't reunite, reunite with a duplicate or reunite in the wrong place mutations occur. Williams syndrome is an example of deletion (the end of a chromosome is lost.)

Jeremy Vest, who has Williams Syndrome is a perfect
example of its carriers natural draw to music.

II. DNA

A. DNA/RNA: Structure and function

DNA, as previously discussed, is the material that contains genetic code. DNA must be able to do three things: 1. Replicate 2. Store genetic information 3. undergo mutations for diversity.DNA structure is a double helix. There are two backbone strands of polynucleotides that contain the paired bases. These bases make rungs across the strands. The bases are Adenine and Thymine (complimentary and pair together) and Guanine and Cytosine (complimentary to each other.) When DNA replicates the strands split and a new strand joins each of the old strands. Then any breaks in the backbone strand are repaired and we have two DNA molecules. When errors occur in replication, they will usually be fixed by enzymes. Those that continue are called mutations.
RNA, instead of having the Thymine nucleotide, has Uracil as a complimentary base to Adenine. RNA is single stranded.There are different RNA with different functions. mRNA (messenger RNA) carries the information from DNA templates to the cytoplasm for DNA synthesis. tRNA (transfer RNA) transfers amino acids to ribosomes for DNA synthesis. Each type of amino acid is carried by a different type of tRNA. rRNA (ribosomal RNA) make up the sub units of ribosomes for DNA sysnthesis.

B. Gene Expression

Proteins (which make up DNA and RNA) are made of amino acids. There are 20 amino acids that commonly make up proteins. Their number and position is what determines the type of protein one will be and the shape it will take. These are, naturally, integral to DNA synthesis and gene expression. The first step is called transcription. This is where mRNA transcribes the DNA template with genetic coding. It is then taken to the ribosome for translation. In translation, the nucleotides of the mRNA transcript are translated into amino acids for for gene expression.This genetic code, of four nucleotide bases, is a triplet code. The bases are read in units of three and each three base-section translates to a certain amino acid. These sections are known as codons. They are read by anticodons which are carried by tRNA that are attached to the correct amino acid for the protein being made.

Translation in progress, as anticodons
place amino acids in the right order.

C. Genomics

Genomics (the study of one's genome or collective heredity information) is, of course, a very important aspect of modern science. The Human Genome Project has been put together to better understand the human genome. They have succeeded in identifying most if not all of the genes of the human genome. The future goal is to understand a genes specific function and how it actually creates a human being. Comparative genomics is an attempt to determine the evolution of species, namely humans. They have, in doing so, made interesting insight to human disease and would hope to find more links to diseases.
Since proteins are often translated from genes. There is much to be studied in them IBM's "Blue Gene" supercomputer is one endeavor in proteomics, or the study of the proteome. It is also an advancement in Bioinformatics, the study of genomes with computer technology. There are many studies in these areas going on to help improve the human condition. Gene therapy is an applied region of genomics. This is where genetic material is put into the human cells for correction of genetic disorders. This is stil a very young science, but much progress is being made and treatment of many disorders are in the works.

D. DNA Technology

Cloning is a relatively young area of biology. It is the producing of copies of DNA. This is done asexually and technologically. Recombinant DNA is cloned DNA of more than one source. Plasmids in bacteria are a particularly common subject for this process. This way specific genes can be produced, then isolated for use. Polymerase chain reaction (PCR) is a process that takes a small section of DNA and copies the sequence. It has been used to determine DNA strands of mummified brains, identify unknown soldiers, determine fatherhood of posterity and determine perpetrators of crimes. Many products have come from cloning and biotechnology. Many plants have been engineered to be resistant to pests and herbicides. Animals have been given growth hormones to be larger and reproduce faster. The sky is really the limit with this technology.

The genetically modified tomato, on the
right is significantly larger than the
"organic" tomato.The
issue of Genetically Modified
Organisms (GMOs) is a highly
controversial topic.

III. Cancer

A. Cancer cells

Cancer is a name for many different types of diseases that can appear in almost any part of the body. The reason they are called cancer is that they all have certain things in common. Cancer is cellular. Cancer cells are conspicuous and abnormal. The nucleus of cancer cells is irregularly large. They may have abnormal numbers of chromosomes. They fail to experience apoptosis, or irregular cell death. Cancer cells divide indefinitely with the potential to divide limitlessly. They form tumors. They do not respond to cellular growth obstructers. Mutations become more frequent making cancer cells increasingly irregular. Cancer metastasizes, that is invades lymph nodes or blood vessels to inhabit different areas.
Cancer cells have a mutation in one or both of the these genes: proto-oncogenes and tumor-suppressing genes. The proto-oncogenes promote the cell cycle and inhibit apoptosis. The genes are modified they are called oncogenes. This is a "better-working" version. The tumor-suppressing genes are, themselves, supressed or totally diffused.
Oncology is the study of cancer. Oncologists study cancer in all its forms. Some different types of cancer are: lung, colon, pancreas, stomach, throat, lymphoma, leukemia, skin, breast and brain cancers.

Lung cancer cells

B. Cancer causes

Though understanding of of cancer's causes are not complete many things have come to be understood. First cancer can be hereditary. If one inherits certain mutated genes, cancer can occur. Another cause is environmental factors. Some of these are radiation, tobacco smoke, pollutants (asbestos, uranium, radon, benzidine, etc.) and viruses.


C. Diagnosis

Early detection of cancer is an important factor to success of treatment. Many ways are being developed and speculated for very early cancer detection. Those we have available now are physical warning signs, regular screening tests, tumor mark tests and genetic tests.
There are seven warning signs that one can determine the possibility of cancer. They were published by the American Cancer Society. The acronym of these signs spells "CAUTION." these are: 1. Change in bowel or bladder habits 2. A sore that does not heal 3. Unusual bleeding or discharge 4. Thickening or lump in the breast or elsewhere 5. Indigestion or difficulty swallowing 6. Obvious change in wart or mole
7. Nagging cough or hoarsness

D. Treatment

There are many types of treatment for cancer. Some have been used for a long time with nominal success. Others are simply being tested which will, hopefully, prove successful. The standard types of treatment are radiation, chemotherapy and surgery. Radiation therapy is when radiation (gamma rays, or X-rays) are applied to a specific, cancerous area. Radiation causes disruptions in chromosomes and more easily kill cancer cells, specifically. Surgery is used to remove cancer in situ (non-base penetrating cancer.) Chemotherapy is drug injection that kills cells. The idea is to kill as many cancer cells as possible while maintaining enough normal cells for the body to function.
Some more experimental therapies are immunotherapy (injection of cancer-killing antibodies), p53 gene therapy (genetic expression that catalyzes aptosis in cancer cells) and antiangiogenic drug therapy.

Chemotherapy makes the body weak
and is often marked by body hair loss.

IV. Genetic Inheritance


A. Genotype vs. Phenotype

Genotypes are the genes of an organism. Alleles are specific types of traits in a gene. There are two alleles for each genotype and they affect the same trait. A familiar and basic way to look at this is is to chose a specific trait, such as that for freckles. The letter "f" is designated to this trait. Each allele would represent whether the trait would be freckles or no freckles. The allele for freckles is dominant, there fore it would be represented "F" whereas the recessive allele would be represented "f." If a person has freckles their genotype would, then, be "FF" or "Ff." The first form, "FF" is called homozygous dominant. This means that both alleles are the dominant. The second is called heterozygous, meaning both alleles are present. When a genotype is heterozygous the phenotype (expressed trait) is always the dominant. If a person had no freckles, the genotype would "ff. " This genotype is called homozygous recessive.

B. One and two-trait inheritance

When an organism has only one trait, such as "FF" expressed above, the only allele the gamete would pass on is a dominant allele. The same is true if the organism were homozygous recessive. Now, if a heterozygous trait were present half of the gametes would carry the dominant allele, and half would carry the recessive allele, since the chromosomes split in half during meiosis. To figure out the possibility of a trait in offspring one would, simply, make a punnett square. This square is divided into four spaces with the alleles of one parent on the top and the alleles of another parent on the side. Combining each set of alleles in the corresponding square gives the possible outcomes of an offspring. When an offspring is heterozygous the individual is a monohybrid, because one trait is hybrid. When two traits are part of the two homologous chromosomes in meiosis1 there become four allele setups (i.e. widow's peak: W, or w, short fingers: S of s: possibilities WS, Ws, wS, ws.) These can be lined the same way on a punnett square, but instead of having four areas of possibility and probability, there are now sixteen!If an offspring is heterozygous in both traits they are a dihybrid.

A punnett square where "A" or "a" represents
an allele of a trait.

Most disorders are autosomal (not pertaining to sex chromosomes.) Disorder traits are passed on the same way as other genotypes. If a disorder is dominant any autosomal dominant of heterozygous carrier will be affected by it. If it is a recessive disorder than only those carrying autosomal recessive genotypes will be affected by it. If the disorder is recessive a child may carry a disorder that neither parent has. If the disorder is dominant than the child with it will virtually have to have a parent with it. However the child may not if the parent or parents do.There are many autosomal genetic disorders. Some recessive ones are Tay-Sachs disease, cystic fibrosis and sickle cell disease. Some dominant disorders are Marfan syndrome and Huntington disease.

C. When it's more than that

There are some traits that are controlled by multiple sets of alleles. These are called polygenic traits. Polygenes are often subject to the environment. Whenever large groups of people are surveyed for phenotypes of polygenes, the trend shows a belly type curve. Since dominant alleles will most likely be found in most of these people and because of environmental effects there will be a continual distribution.
Some phenotypes will have incomplete dominance or codominance. That means that neither trait takes dominance and a mixed phenotype shows up. Such as a wavy haired child coming from parents of which one has straight hair and the other curly. Some disorders act in this way.

D. Sex-Linked Inheritance

Most traits are autosomal, since 22 of the 23 chromosome pairs are autosomes. However, a few disorder are sex-linked, meaning they occur on the X or Y chromosome. Very few genes are on the Y chromosome (which, usually, only men have.) Most sex-linked traits, therefore, come from the X chromosome. Since this is true traits can be passed to either offspring from either parent.
The same is true for the sex-linked disorders. When int is an X-linked recessive disorder it is usually expressed more often in males than in females. That is because when an X-linked disorder is recessive the male only receives the recessive trait. The Y chromosome doesn't have an allele for it. Some of these are color blindness, muscular dystrophy and hemophilia.

Hemophilia, an X-linked recessive disorder
makes carriers susceptible to extensive
bleeding since they lake adequate
blood clotting proteins.

"IBM Research."http://domino.research.ibm.com/comm/research_projects.nsf/pages/bluegene.index.html

"tomatoes."http://www.american.edu/TED/images4/tomatoes.jpg

"Lung cancer."http://www.scienceclarified.com/scitech/images/lsbv_0001_0001_0_img0030.jpg

"Christi12"http://www.christithomas.com/images/MVC-003F15.jpg, used with permission.