Chapter 5 - 2/12/2008 "Sex Determination and Sex...

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2/12/2008 1 Chapter 5 “Sex Determination and Sex Chromosomes” Sexual Differentiation and Life Cycles Chromosome Composition and Sex Determination The X Chromosome and Dosage Compensation Temperature Variation and Sex Deter. In Reptiles 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. 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. Sexual Differentiation 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 in on individual Bisexual- One individual has both sexes Monoecious - plant (from Greek work, one household) Hermaphroditic -plant and animals
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2/12/2008 2 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) 1. Green algae- ( Chlamydomonas ) 2. Field Corn- ( Zea mays ) A monoecious plant that has both male and female organs on
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Chapter 5 - 2/12/2008 "Sex Determination and Sex...

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