Unit 2 Compendium Review

Genetics Compendium Reviews
Genetics is responsible for the way people look, respond, and there susceptibility to hereditary and environmental diseases. Understanding how genetics works and how genes are passed on to offspring is vital to human development. When we discuss genetics there are two main cases, cell division in mitosis and cell division for sex cells meiosis. Both of these cellular divisions process are important and when genetic malfunctions occur the results can be detrimental in the worst and debilitating in the least.


Cell division
For cells in humans to divide the DNA in the double helix form is wrapped with protective proteins called chromosomes, when DNA is not dividing it is in a medium liquid surrounded by chromatin. The formation of exact replications of chromosomes allows for cell division and two exact sister copies of the parent cell. Cells must divide to repair damaged or dying parts of the body, or to allow the body to grow for individuals who are still young and not fully developed.
As stated there are two main types of cell division mitosis and meiosis. Mitosis is the process where two identical sister cells are made from on parent cell. These cells can then perform the same function as the parent cell and also divide to continue the process of producing two identical copies. In meiosis the parent cell has 23 pairs of chromosomes (called a karyotype) these chromosomes pairs have one chromosome from each parent for a total of 46 chromosomes (2n=4). These chromosomes represent the genes and genetic trait’s the offspring will have (also called a genotype). During the process of meiosis the parent cell divides into two daughter cells with each daughter cell having half of the parents chromosomes (n=2). These two daughter cells then divide again to form a total of four haploid cells. Each haploid cell now has just one member of the parent chromosome for four haploid cells each with n=2, this cell is called a gamete. The gamete is the sex cell for men and females, when two gametes join they then each share there compliment of chromosomes to make a zygote cell that has 23 pairs of chromosomes or 46 individual chromosomes. The zygote now has the genetic traits of both parents and yet is different from either parent.


The four phases of Cell division in mitosis
The cell also has its own cycle called the cell cycle where there are two orderly process, the interphase and cell division. I will mostly be covering cell division.
The four phases of cell division are prophase, metaphase, anaphase, and telephase. In as the cell divides there is distinct break in that represents each of these phases. In fact these phases are only used to better organize a process that is fast, smooth and continuous. The advantage to describing the cell dividing process with these different phases is because the process of cell division can be stopped and these phases can then be seen under a microscope.
Prophase = During this phase the chromosomes condense and become visible under a microscope. The nuclear envelope fragments and the nucleolus disappears completely. Spindle fibers start to appear and attach to the centromere. The centromere is where the spindles develop from, which help to separate the chromosomes and pull them to opposite pulls. The centrosome on the other hand is the center location of the chromosome and holds the pairs together, the centrosome will be pulled apart by the spindles.
Metaphase = In this phase the chromosomes line up in the center of the cell also known as the equator and the spindles are fully formed and overlapping on the outsides.
Anaphase = In this phase the sister chromatids start to separate by the spindles pulling on the centrosome and pulling them to opposite pulls.
Telophase = In this final phase the chromosomes are at opposite pulls and breakdown to chromatin again as the nucleoli reappears for each set. As the nuclear envelope starts to reassemble there is a cleavage furrow associated with the cytokinesis (division of cytoplasm and organelles) which starts to separate the cytoplasm and form two daughter cells.
In the process of producing a the gametes the original parent cell undergoes 8 different phases broken down into meiosis 1 & 2. The process is very similar to the phases in mitosis but in the end instead of two identical sister cells, meiosis produces 4 haploid cells with only half the number of chromosomes of the parent cell.


Alleles = The genotype refers to a specific gene the offspring will inherit from the parents. The phenotype is the physical presence of the genotype. The genotype for a individual could be for blue eyes. When that individual develops the blue eyes you have the phenotype. The allele is the code given to that particular trait such as “B” for a dominant allele for blue eyes, and “b” for a recessive allele for blue eyes.


DNA has special qualities which make the process of DNA transcription very efficient and quick. The primary feature is the double helix strand which is a trait for all DNA. The two complementary strands can unwind and special proteins can combine with the originals strands to form new identical DNA molecules.

Chrosomes = Are DNA molecules wrapped in special proteins giving the DNA a particular shape.

Gene expression = Is the term used to describe a particular section of a DNA code which proteins are made from to catalyze certain chemical reactions in cell metabolism. The process uses messenger mRNA which takes the DNA outside of the nucleus to the ribosome’s where amino acids take the encoded information and fold in a complex manner to make a protein.
Regulation of gene expression = The cell does not want all parts of the DNA gene making proteins all the time, so regulation is used to make sure only the genes needed for a particular chemical reaction are being produced. There are four major ways this is accomplished, transcriptional control, posttranscriptional control, translational control, and posttranslational control.


Controlling the process of genes and there for the metabolism of a cell are extremely important. When the process to control gene production and cell division fail the safeties are off and cancer can be the common result. With cancerous cells there are no safeties, the cells can divide with out restraint. The process for cancer starts with one cell going awry, and developing mutations which allow it to divide indefinitely, this process is initiation. In promotion a tumor develops which can either be encapsulated locally meaning it does not travel to other parts of the body or it can mutate and be able to invade other organs called progression. If the tumor cells are able to attack other organ parts and cells it has reached metastasis and can invade areas far from the origination location of the first cancer cell. This process is not supposed to happen in normal cell development and division, but when genetic or environmental factors with health problems become an issue it is much easier for these cancerous cells to occur.

Apoptosis = This is the term used for the automatic death of cells. Cells are designed to die after they have divided a preprogrammed number of times. There are a variety of factors involved but in cancerous cells the ability for the cell to die when it should does not occur.
Telomeres = Are the DNA sequence which programs the cell to undergo apoptosis when it should.


The term tumor refers to cancer cells which have continued to divide and have formed layers on top of each other. There are many individuals who have genes which cause cancers cells, these genes are called oncogenes. Cancer is also known to develop by mutating two types of genes. The proto-oncogenes is a code for proteins which promotes the cell cycle and prevents apoptosis. This gene will allow apoptosis at the right time but if it becomes mutated the cell cycle can just continue with out dying.
The other gene is tumor-suppressor genes which stop the cell cycle and promotes apoptosis. When this gene is mutated then again the cell cycle will continue without stopping.
Oncology is the study of cancer, and oncologists are doctors who treat and study cancerous cells. When a person is shown to have metastasis tumors which have invaded other parts of the body there chance for survival drastically goes down.
Tumors are classified in relation to which part of the body they affect.
Carcinomas = Cancer cells in the epithelial tissues, including skin, breast, liver, pancreas, intestines, lung, prostate, and thyroid cancer.
Sarcomas = Are cancers in the muscle and connective tissues like bone, and fibrous connective tissue.
Leukemia’s = Cancer of the blood.
Lymphomas = Cancer of the lymphatic tissue.