Meiosis

When does crossing-over occur?

It only occurs in prophase I when synapsis occurs

In what stages of meiosis are the cells diploid and in what stages of meiosis are the cells haploid? why?

(PMAT I)In meiosis I, the cells are diploid because there are homologs. However, once cytokinesis occurs and meoisis II begins, the cells are all haploid. (PMAT II)The second stage of meoisis is haploid because there is no replication of DNA between meoisis I and meoisis II.

What are some causes of cancerous cell growth and what is the difference between malignant and beign tumor?

*Cancerous cell growth is the uncontrolled reproduction of some body cells. this can be caused by the oncogene being turned on. Enviromental factors, diets...can cause the oncogene to be turned on. Other factors that can cause uncontrolled cell growth include...mutated tumor suppressor gene. Exposure to carcinogen (cancer causing substance)-most carcinogene are mutogenes* A benign tumor does not spread, where as a malignant tumor can. --Uncontrolled growth of cells, cancer, is caused by a mutation in proteins that causeses the protein not to function properly. cell growth and division are disrupted as a result. --Malignant (cancerous): Abnormal cells divide uncontrollably and destroy body tissue (Invades adjacent tissue, CAN spread) --Benign tumor: mass of cells (tumor) that lacks the abiltiy to invade neighboring tissues (serious if press on vital sructure, blood vessels or nerve cells)

Explain oogenesis. Also define a polar body, and state how many eggs (gametes) are produced from one germ cell (an immature sex cell) and how many polar bodies are produced.

*Oogenesis is the process that results in the production of a n egg (ovum or ova). It begins with a diploid germ cell in the ovary that enlarges and becomes the primary oocyte. It then goes through meiosis I and meoisis II creating four haploid cells. However as it goes through meoisis, one cell accumulates more cytoplasm than the others. This large cell becomes the haploid cell and the other three small cells are polar bodies. The polar bodies disintegrate.* Oogenesis is the production of mature egg cells, or ova. During cytokensis & cytokensis II, cytoplasm of the original cell is divided unequally between new cells. One cell recieves most of the cytoplasm (one egg produced), and the other products of meiosis, polar bodies, eventually will degenerate. *1 mature egg produced and 3 polar bodies*

Explain spermatogenesis. Also state how many sperm (gametes) are produced from one germ cell (an immature sex cell).

*Spermatogensis is the process that results in the production of sperm. It begins in a diploid germ cell in the testes that enlarges and becomes the primary spermatocyte. It then goes through meiosis I and then meoisis II to produce four haploid sperms* Spermatogensis is a process in male animals to produce gametes. Inside the male reproductive system, diploid germ cell grows in size. It becomes a primary spermato cycle, a large immature cell that enters meiosis and cytoplasmic division. 4 haploid cells result and develop tails, thus becoming a sperm, a type of mature male gamete. *4 haploid cells or 4 gametes*

What are stem cell and how can they be used? What are the moral implications of the use of embryonic cells?

*Stem cells are undifferentiated cells that have the potential to be manipulated to become any type of cell...to be used to replace damaged/diseased cells...Some corcinogens include- tobacco smoke, asbestos, radiation such as x-rays, ultraviolet light (UV), some viruses (ex. cervical cancer or human papiloma virus)* --Stem cells: Early stage, have not decided what type of cell to be (muscle, nerve, skin, etc.) Unspecialized cells hat give rise to the different types of cells that make up the human body. --Embryonic stem cells harvested from human embryos cause the embryo to be destroyed. --Many people belive that is unethical to destroy embryos that have the potential to develop into babies.

Define homologous chromosomes (also calld homolgues and homologs), synapsis, tetrad (bivalent)

---Homologous chromosomes, homologs, homologues: Chromosomes that are the same length, shape, and have the same gene sequence. They may have different allele versions of a gene, but will have the same genes. One homolog is inherited from the mother and other is inherited from the father. Diploid cells are diploid because they have two of each type of chromosome...in other words, they have homologous chromosomes ---Synapsis: Homologous chromosomes line up side by side, then they stick together during Prophase I -(Tetrad) The homologs are said to form a tetrad when in synapsis -Tetrad (bivalent): 2 chromosomes with the attached sister chromatids

Explain how crossing-over provides genetic recombination thereby leading to genetic variation in the offspring.

-Crossing over switches sections of one chromosomes with the same section on its homolog. So a chromosome is no longer 100% identical to either parent. This helps combine genes in unique ways which leads to variation in the offspring. -Crossing over is the exchange of segments of DNA, and results in chromosomes that are a mix of each paternal and maternal chormosome, therefore they are genetically unique.

When does independent assortment occur and what leads up to this being able to take place?

-It occurs during Anaphase I - Independent assortment is really set up during Metaphase I by the randomeness of which homolog is on which side of the equator of the cell.

What are the three important results of meiosis?

-haploid cell -4 haploid cells -genetically unique

What are three things to contibute to genetic diversity in sexual reproduction?

Crossing over, independent assortment, & randomness of which sperm and egg end up coming together in the process of fertilization to form the zygote.

Explain the difference between genes and alleles.

Genes are heritable sections of chromosomes that code for a protein or a part of a protein. That protein controls a trait. Alleles are variations of a gene. For example, agene may code for a blood type and there are allele verisons for a type A, type B, and type O blood. --Alleles: Different versions of genes; One of the alternative forms of the gene that governs a characteristic (hair color) --Genes: made of DNA, which transfers hereditary material through generations; contains instructions for a single trait.

Explain what independent assortment is and how this leads to genetic variation in the the offspring.

Independent assortment is after homologues form a double line on the equator. Also, it is totally random which side of the equator the homolog will be on, the randomness leads the diversity of gamete when they are seperated. -Independent assortment is the pulling apart of homologs, pulling a random mixture of maternal and paternal chromosomes toward opposite poles. -It leads to gentic variation because it leads to the combination of a unique mixture of paternal and maternal chromosomes in the final haploid cell

List and describe the stages of meiosis in order. Be able to match each stage to its picture.

Meisos I *(Cells Diploid)*: >>>>>Prophase I: -Nuclear evenvelope breaks up, centrioles moving toward oppostie poles, kinetochore microfilaments attach to centromeres once envelope is gone; Homologs are in synapsis and form tetrads. Crossing over occurs between homologs -Nuclear membrane & nucleous disappear -Spindle fibers appear & attach to chromosomes -Synapsis: Homologous chromosomes line up side by side & stick together *NOTE: Synapsis => Tetrad* >>>>>Metaphase: -Homologs line up side by side at equator of the cell -Tetrads of prophase I moved by spindle fibers to equator & homologues form a double line >>>>>Anaphase I: -Homologous seperate, one chromosome pulled by spindel fibers to opposite poles >>>>>>Telophase I: -Homologs are at opposite poles from each other. cleavage furrow forms in animal cells and cell goes thru cytokinesis (once cytokinesis occurs, it is in the next phase and there are now two halpoid cells) Meosis II *(Haploid cell)*: >>>>>Prophase II: -kinetochore microtubles move chromosomes toward equator of cell -Chromosomes of plants recoil, spindle reforms -Chromosomes attach to microtubles (as in mitosis) >>>>>Metaphase II: -Chromosomes are at equator of cell -Marked by completion of spindle apparatus & migration of chromosomes to equator >>>>>Anaphase II: -sister chromatids are seperated and pulled away from each other to opposite poles -Centromers divide, liberating each sister chromatid -Former chromatids (individual chromosomes) pulled to opposite poles by kinetochore microtubles. >>>>>>Telophase II: -Nuclear envelope forms around chromosomes (there are now four haploid cells after cytokinesis) -Cytokinesis, nuclear envelope reform, & chromosomes relax into extended state -Cyotplasm divided => Total 4 haploid cells formed

Compare and contrast mitosis and meiosis.

Mitosis and meoisis both are types of nuclear division seen in eukaryotic cells. They both have similar phases, PMAT. However, mitosis results in two diploid cells that are identical to the original cells while in meoisis results in four haploid cells that are genetically unique from the parent cells and from each other. Mitosis has only one cycling through PMAT, while meoisis cycles through PMAT two times back to back with no replication of chromosomes between the two cycles. Meoisis has the formation of tetrads and crossing over in Prophase I that does not occur in mitosis. Mitosis occurs in somatic cells of eukayotes while meoisis occurs in sex cells (germ cells) of eukaryotes. *Refer to worksheet* Mitosis: -Daughter cells gentically identical to parent cells -2 daughter cells -Asexual reproduction -diploid (having to do with chromosomes) Meiosis: -Daughter cells genetically unique to parent cells -4 daughter cells -Haploid (having to do with chromosomes) -Sexual Reproduction Both: -Occur in phases -Division of cells -Type of cellular reproduction

What type of nuclear division is used for the following examples: a) replace old dead skin cells b) produce a spore c) produce daughter cells with genetic variability d) produce buds e) to add roots and shoots from plant cuttings f) to make gametes g) to make somatic cells (somatic cells are non-sex cells)

NOTE: Body cells - Mitosis; Sexual reproduction-Meiosis a) Mitosis b) Meiosis c)Meiosis d) Mitosis e) Mitosis f) Meiosis g) Mitosis Mitosis is seen when body cells (somatic not germal) are being replaced. examples of this are seen when dead skin cells are replaced, buds are green, plant cuttings grow roots and shoots...any somatic cell is replaced. However, meoisis occurs to make haploid cells that are genetically unique...which leads to genetic variability...this is seen in the production of spores and the production of gametes (egg, sperm)

What is the non-disjunction and how does it lead to aneuploidy? What is aneuploidy?

Nondisjunction is when chromosomes, either homologs or sister chromatids, do not seperate during one of the anaphase stages. This results in some gametes having too many chromosomes and some gametes are having not enough chromosomes...which is aneuploidy (not having the correct number of chromosomes).