Chapter 5 notes

Chapter 5 notes - Chapter 5 "Sex Determination and Sex...

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Chapter 5 “Sex Determination and Sex Chromosomes” Sexual differentiation plays an important role during the life cycle of various plants and animals. While a single pair of sex chromosomes often play an important role in determining sexual maturation, genes present on these chromosomes as well as on autosomes serve as the underlying basis of sex determination. In humans, genes on the Y chromosome cause maleness, and in their absence, female development occurs. Mechanisms have developed to compensate for the dosage of genetic expression in organisms where one sex contains two X chromosomes, while the other has but a single X chromosome. In mammals, random inactivation of one of the X chromosomes in the compensatory mechanism. Still other modes of sex determination have evolved. Reptiles exemplify environmentally induced sex determination, where the temperature during the incubation of eggs is the critical factor. 5.1 Sexual Differentiation and Life Cycles 95-98 5.3, 5.4 Chromosome Composition and Sex Determination 99-104 5.5 The X Chromosome and Dosage Compensation 104-107 5.7 Temperature Variation and Sex Deter. In Reptiles 109 5.1 Sexual Differentiation and Life Cycles Sexual differentiation differs greatly among organisms. We tend to only think about mammals that have distinct sexes that are phenotypically and genotypically different. However, many organisms handle sexual differentiation and procreation quite different than mammals. Some terms: Organisms that have two distinct sexes Unisexual- One sex per individual (male and female) Dioecious- plants (from Greek word, two households) Gonochoric- animals Organisms that have both male and female organs Bisexual- One individual has both sexes Monoecious- plant (from Greek work, one household) Hermaphroditic-plant and animals Some examples of how organisms handle sex 1. Green algae- ( Chlamydomonas ) Spend most of their life in the haploid state Show infrequent periods of sexual reproduction Opposite isogametes (n) pair and fuse to form the zygote (2n) See Figure 5-1
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Note: Many fungi follow a similar life cycle of spending most of their life in the haploid state. Other fungi do not have a known sexual cycle (aka. fungi imperfecti). 2. Field Corn- (
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This note was uploaded on 02/20/2008 for the course SORC 330 taught by Professor Brick during the Spring '08 term at Colorado State.

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Chapter 5 notes - Chapter 5 "Sex Determination and Sex...

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