Lecture_6_Sex_Determination_&_Linkage_2011

Lecture_6_Sex_Determination_&_Linkage_2011 - Sex...

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Sex Determination,Sex Linkage Jan 24 th, 2011
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Announcements Homework due on Friday at 4 pm in TAs mailbox
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Review DIHYBRID crosses between heterozygotes result in a 9:3:3:1 ratio 9:3:3:1 ratios contain two independent 3:1 ratios The SUM and PRODUCT rules can be used to derive probabilities for multi-hybrid crosses BINOMIAL EXPANSION can be used to determine the probability of a set of events
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How is Sex Determined? Hermann Henking (1891) found “X-body” in the nuclei of male grasshoppers Clarence McClung called it the X chromosome The XX – XO system is the simplest (O = absence of chromosome) Males are heterogametic: XX Females are homogametic: X0
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XX – XY System In many species both genders have the same number of chromosomes but one pair is heteromorphic The smaller chromosome is called the “Y” First identified by Nettie Stevens, 1905, in the mealworm Tenebrio Genes on the Y chromosome are responsible for sex determination Non-sex chromosomes are called AUTOSOMES
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Sex Chromosomes Human Karyotype
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Human Sex Chromosome Phenotypes Wildtype: XX (female) or XY (male) OO is lethal XO leads to Turner syndrome (1/3000) – female Monosomic: missing one chromosome • X n Y n leads to Klinefelter syndrome (1/1000) – male Trisomic: extra copy of one chromosome XXY (47, XXY), XXYY (48, XXYY) • X n are Poly-X females (1/1000)
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This note was uploaded on 02/17/2011 for the course BIOL 202 taught by Professor Kieber-hogan during the Spring '08 term at UNC.

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Lecture_6_Sex_Determination_&_Linkage_2011 - Sex...

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