Chapter Eight

Key Terms:
Haploid cells- half the number of chromosomes (23 for humans)
Control mechanisms- cells divide rapidly, often in the absence of growth factors
Polyploid- many chromosomes
Nondisjunction- An accident of meiosis or mitosis in which a pair of homologous chromosomes or a pair of sister chromatids fail to separate at anaphase.
Diploid- In an organism that reproduces sexually, containing two homologous sets of chromosomes, one from each parent.
Karyotype- shows stained and magnified versions of chromosomes
Chiasma- The ricroscopically visible site where crossing over has occured between chromatids of homologous chromosomes during prophase I of meiosis.
Getnetic recombination- the production of gene combinations different from those carried by the original chromosomes.
Sex Chromosomes- the X and Y chromosomes that determines a chromosomes sex (XX female and XY male)
Autosomes- other 22 pairs of chromosomes
deletion-loss of a chromosomal segment
duplication- a copy of a chromosomal segment
inversion- reversal of chromosomes
translocation-can be reciprocal;switched

Reading Journal:
1) What 'accidents' can occur during meiosis and what is a possible result?
You can have more chromosomes than you needed. this would result in a slight mutation and variation.
2) How are Karyotypes produced? Karyotypes are produced from dividing white blood cells, stoppped at metaphase.
3) How does cancer form? Growth is not inhibited by other cells, and tumors form and eventually spread through the blood system if it is not caught early.

Five Facts:
1)Carcinomas arise in external or internal body coverings.
2)Trisomy 21 involves in the inheritance of three copies of chromosome 21
3)Altered chromosomes carried by gametes cause birth defects
4)Chromosomal alterations in somatic cells can lead to cancer
5)Locacalized tumors can be treated with surgery or radiation, while Chemotherapy is used for metastic tumors.

Cell Division is important to the reproduction of cells and organisms, because new cells can only come from already existing cells.
Mitosis distributes duplicated chromosomes into two daughter cells. After chromosomes form, the spindle fiber appears and the microtubles move to the middle of cell. The spindle fiber then separates the sister chromatids apart and two nuclei form. A cleavage furrow will appear in animal cells, a cell plate in plant cells. Cytokinesis takes place, and fully separates the cytoplasm apart. Some important functions for mitosis include for growth, replacement, asexual reprodution, and occurs in somatic cells.
Meiosis occurs for sex cells. All of what takes place during mitosis occurs during meiosis, but with an extra process after. Also happening during meiosis I, is a process called crossing over. in crossing over, homologous chromosomes exchange the same segements. Meiosis II just separateseach homologous pair and produces two daughter cells. Separation of homologous chromosomes(crossing over) during meiosis leads to genetic differences between gametes.
In down syndrome, or trisomy 21, the incidence increases with the age of the mother. Trisomy 21 is caused by having an extra copy of chromosome 21. Down syndrome is characterized by
characteristic facial features, susceptibility to disease, shortened life span, mental retardation, and variation in characteristics.
Cancer cells are characterized by dividing excessively, where growth is not inhibited by other cells. These form masses of tissue called tumors. There are two types of tumors, malignant, which can invade other cells, and benign, which are less harmful. Radiation and chemotherapy are the most effective ways of treating cancer because they are able to interfere with cell division, thus stopping the cancer cells from growing.

Here is a karyotype of Trisomy 21, Aka Down syndrome. Here, there is one extra copy of chromosome 21. Other types of syndromes can occur if there is an extra copy of any chromosome, such as trisomy 13, trisomy 18, etc.
A karyotype is formed by dividing a white blood cell and stopping it during metaphase, so that it is easier to read.





Video Link Meiosis:
dividing white blood cells, stoppped at metaphase