bio214f - Biology 214/414 2009 Packet #5 Suggested...

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2009 P a c k e t # 5 Suggested problems: Chapter 7: 4, 5, 6, 7, 10, 14, 16, 17, 18, 19, 21, 22 Sex determination I. Mechanisms of sex determination a. XX , XO (where “O ” indicates no chromosome) ( Figure 7-5a ) i. This type occurs in several insects, including grasshoppers. ii. In grasshoppers all gametes will have one each of 11 autosomes and either 1 or no X chromosomes (either 11 or 12 chromosomes per gamete). iii. Regarding reproduction in grasshoppers the males (XO) will produce ½ X and ½ O gametes and the females (XX) will produce all X gametes. Thus 1 x ½ = ½ of the offspring will be XX (females) and 1 x ½ = ½ of the offspring will be XO (males). iv. This provides for equal numbers of the two sexes in the offspring, and is thus a good strategy for continuation of the species. b. Some organisms have XO as females and XX as males. c. A more widespread mechanism is to have one sex be “heterogametic ” (XY or ZW, that is producing gametes with different sex chromosomes) and the other to be “homogametic (XX or ZZ, that is producing gametes with only one type of sex chromosome). ( Figure 7-5b ) i. Usually XY and XX ( Drosophila , humans, most higher animals, some “dioecious ” plants). ii. Some birds, moths, butterflies, reptiles, and fish have ZZ males and ZW females. iii. Regarding reproduction, consider humans (XX females and XY males) as an example. All eggs will contain an X, while half of the sperm will contain an X and half a Y. Thus 1 x ½ = ½ of the offspring will be XX (females)
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This note was uploaded on 03/03/2010 for the course BIOL 214 taught by Professor Stark during the Fall '06 term at Illinois Tech.

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bio214f - Biology 214/414 2009 Packet #5 Suggested...

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