Warm Up 7 is due Wednesday March 3, 2004, at 9:30 am

QUESTION 1: Which gender is doing more meiosis RIGHT NOW in class - the males or the females? Or do men and women undergo meiosis at pretty much equal rates? What type of cell is the end product of meiosis in men? What type of cell is the end product of meiosis in women? How many chromosomes do these cells have compared to our other body cells?

From Jessie: Men undergo meiosis more than women because women only have a certain number of eggs and men are able to make as much sperm as they will ever need. the end product in men is sperm and eggs in women. these cells have half as many chromosomes as other body cells.

From Beth: Males because all of the females egg cells afre developed before birth! The men are canstantly developing sperm cells. They each have 23 chomasomes so that when that meet up the create one cell with 46....a baby!

From holla back: Males are undergoing more meiosis right now because they can produce millions of sperm as opposed to females only being able to produce to ova at a time. In males they start as a primary spermatocyte and that cell begins meiosis and turns into spermatids They change in form developing a head and a tail and are then known as sperm. In females they begin as oocyte and go through a process known as oogenesis. In the end they are called ova. I'm not sure about the chromosomes but i think they have 23.

QUESTION 2: A common error in meiosis in an egg (or a sperm) can result in trisomy ('three-chromosomes'), in which each somatic cell of the of baby has 3 copies of one particular chromosome. Trisomy 21 is when an individual has not 2 but 3 copies of Chromosome 21 in every one of their cells. Trisomy 21 is also called Down Syndrome. What do you think happens in meiosis that would result in 3 copies of Chromosome 21 in an embryo? Do you think there are other trisomys in humans?

From echo: I'm not sure if I understand this, but I'm guessing happens is that one pair of chromosomes doesn't seperate. I would also guess that if trisomys happen in other chromosomes, there's a good chance of a miscarriage. That said, it probably happens on other chromosomes as well.

From skinny: Three copies of a chromosome would be in one cell if the second division of the chromosomes didn't happen for that particular one, therefore resulting in 3 chromosomes in one cell and only one in the other. Yes there are probably other trisomys in humans.

From Jane: Many errors can occur during cell division. In meiosis the pair of chromosomes are supposed to split and go to different spots in the diving cell. This event is called disjunction. However ocassionally one pair doesn't divide. And the whole pair goes to one spot. This means that in the resulting cells one will have 24 chromosomes and the other will have 22 chromosomes. This accient is called nondisjunction. In down syndrome 95% are caused by this event. This would leave me to belive other trisomy's exist in humans.

From good thinkin: i really have no clue why there might be three copies of a chromosome in the cell. maybe you can explain it to me sometime. for the second question, yes i do believe there are other trisomys in humans because if there wasnt then "trisomy 21" would just be called "trisomy". good thinkin huh. :)

From Dr. Marrs: During meiosis in an egg (or a sperm) sometimes the HOMOLOGOUS chromosomes fail to separate during meiosis 1. This is called non-disjunction and results in one egg ending up with an extra chromosome (24 in the egg or sperm) and the other cell ending up with 1 fewer chromosome (22 in the egg or sperm). Fertilization of this egg results in 3 copies of that chromosome instead of 2 copies. Trisomy 21 (Down syndrome) is one of the only viable trisomys in humans. Many children with Trisomy 21 die in utero, but those born alive have the condition called Down Syndrome, and have an extra copy (3 total) of chromosome 21 in each and every one of their trillions of cells. Two other common trisomys are Trisomy 18 and Trisomy 13; both these trisomys are typically fatal in early childhood. Other trisomys occur, but the pregnancy cannot continue....

QUESTION 3: During development of the human embryo (or any vertebrate embryo), a process called gastrulation occurs. Read the notes for details. Louis Wolpert, a famous embryologist, once made this remark: "The most important event in your life is not birth, marriage, or death, but gastrulation." From an embryological standpoint, why IS gastrulation one of the most important events in your life? :)

From B-rad: This is when the cells start to arrange themselves into their respective "niches" and start to become organs. Without this stage, we wouldn't have our skin, muscles, and heart develop into working parts of our bodies.

From cas: Gastrulation is the process where major cellular organization takes place. The cells rearrange into three layers that will be the basis for all other development. This is important because this helps to determine what cells will be what. Mess this up

From M.K.: Gastrulation begins the process of your cells actually organizing into your essential structures for life: the layers of your skin, your nervous system, your internal organs, your muscles and bones and your heart. This is the process of making the true human form.

From Leashi: This is where major cellular organization happens. The ectoderm, endoderm, and the mesoderm are formed. Also different cells begin toturn on different genes to become different organs. This is where the basic formation of your body takes place.

QUESTION 4: Optional: Questions or comments about Mitosis, Meiosis, or Embryonic Development?

- I'm excited about this section of biology. It's very interesting.
- All I can say is wow! This is the most interesting part of the course thus far. I can't believe there is even a checker to make sure the cells are accurate after mitosis. The brief discussion we had about Cancer helped me to understand the disesase more clearly.It is a very gruesome, horrible situation.
- YIPEE!
- I like this much better than pictures of sugar and starch molecules : )