Warm Up 6 is due Wednesday, February 26, 2003 at 9:30 am.

WarmUp1, WarmUp1 Responses, WarmUp2, WarmUp2 Responses, WarmUp3, WarmUp3 Responses, WarmUp4, WarmUp4 Responses, WarmUp5, WarmUp5 Responses, WarmUp6,

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 grateful student: Q1 = I am going to take a guess on this one. I say men because I think that women are born with all the eggs they will ever have. The end product of meiosis in a man is sperm and in women it is eggs. Each sperm and egg contain 23 chromosomes. Once combined, they will have 46.

From Da Bizzie Fo Shizzie: Q1 = Right now I would have to favor that the males are doing more meiosis. The end product for meiosis in men are sperm cells and for women egg cells. I am not exactly sure about this, but my guess is that each germ cells have half(23)the chromosomes that somatic cells have.

From SpongeBob Biology Pants: Q1 = Hmm...I'm gonna take a wild guess here. The men are doing more meiosis right now (even though I'm not sitting in class, I'm sure they all still are). I'm thinking its the men because from what I am reading in the notes, sperm and eggs are the end result of meiosis and from what I know men are spermie producing machines. And I also know that once a woman reaches a certain age all of her eggs have been produced, so she makes no more. Also, each sperm or egg only has 23 chromosomes, HALF of what normal cells have, because when a sperm and an egg come together, they would make a baby with 46 chromosomes.

From Dr. Marrs: I couldn't have said it better myself! Looks like the men have it as far as meiosis is concerned! Way to go, guys!

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 Mom: Q2 = My guess is that at Anaphase I, when the homologues would normally separate-they don't. This reaction is termed "nondisjunction". The result is a higher number of chromosomes in gametes.
Other trisomys in humans include Klinefelter Syndrome (a sex chromosome abnormality), where a male inherits one Y and two X chromosomes (XXY).

From Willy Wonka: Q2 = This is probably just the result of a sperm or egg being defective and having the extra chromosomes and I imagine that this would be possible for more than just Chromosome 21.

From D'oh!: Q2 = From what I understand, sometimes in anaphase I, a nondisjunction occurs. Some of the chromosomes fail to separate, allowing one set of chromosomes to have an extra one that should have separated. I do believe this does happen in other cases of different kinds of defects such as Klinefelter Syndrome and XYY condition.

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 and the other cell ending up with 1 fewer chromosome. 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. Advanced maternal age correlates with frequency of Down syndrome. 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: Chemicals such as alcohol and nicotine can be teratogens. What are teratogens and why are they so dangerous for a developing baby? What does the name teratogen mean? How can heat (like from a fever or use of a hot tub in early pregnancy) be a teratogen?

From Lucky: Q3 = Teratogens are chemicals, viruses, ionizing agents or environmental conditions that cause malformations in an embryo or fetus. The linguistic roots translates teratogen to mean 'producer of monsters'. Raising the body temperature of a woman 6 weeks pregnant or less can cause neural tube disorders. Such disorders include water on the brain, spina bifida and anencephaly (open skull defect).

From Pavonine: Q3 = Teratogens are drugs or environmental factors that may cause deformties in a developing embryo or fetus particularly in the 3rd to 20th week of pregnancy. Not exactly sure what teratogen means but according to the OED it seems to have something to do with production of monstrosities - presumably in the biological sense this would mean deformities. Heat could be a teratogen because it interferes with homeostasis.

From Dr. Marrs: Teratogens are chemicals or environmental factors that can cause problems to a developing fetus. Often ,they interrupt growth of a vital organ, or suspend normal cellular activity, so that crucial developmental processes that should be going on in cells are skipped, resulting in a birth defect. Teratogen literally means 'making a monster'. Heat (like from a fever or use of a hot tub in early pregnancy) can also cause normal cellular processes to be put 'on hold' until the fever of heat goes away, resulting in a 'skipping' of normal cellular processes,

QUESTION 4: Would you do me the favor of answering a few more questions to help me understand how YOU learn? (PS. I will not read these responses, but a student grader will...so I won't know your answers to these questions - and wouldn't be offended by your honesty anyway! Thanks !)

Thanks for your answers on this question!

The text of this "What is Biology Good For" exercise is copyrighted under the name of Dr. Kathleen A. Marrs, 1999, 2000, 2001, 2003. There are no restrictions on its use by educators or by non-profit institutions as long as its content not modified, proper copyright acknowledgement is retained, and this statement is not removed.

****************************************************************