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Chapter 5 Notes.docx

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Department
Biology
Course
BI226
Professor
Robert Boulianne
Semester
Fall

Description
Chapter 5 – Sex Determination and Sex Chromosomes • Heteromorphic Chromosomes – Eg. X and Y • Unisexual, dioecious and gonochoric – Contain only male OR female reproductive organs • Bisexual, monoecious and hermaphroditic – Contain both male AND female reproductive organs • Intersex – Individuals of intermediate sexual differentiation…usually sterile Modes of Sex Determination • Protenor mode (XX & XO) • Lygaeus mode (XX & XY) or (ZZ & ZW) • In both cases one sex produces two types of gametes (heterogametic sex) while the other produces only one type of gamete (homogametic sex). Klinefelter Syndrome 47,XXY • Testes underdeveloped and fail to produce sperm • Tall, long arms & legs, large hands & feet • Slight decrease in intelligence (below normal range) • Result of nondisjunction event in parent Turner Syndrome 45,XO • Female external genitalia and internal ducts • 1 in 10,000 female births • Ovaries not fully developed • Short stature, skin flaps on back of neck and underdeveloped breasts. Shield-like chest. • Intelligence is normal • Result of nondisjunction event in parent. 47,XXX Syndrome • Occurs in about 1 of every 1,200 female births. • Observe variable expression: – Some XXX individuals are phenotypically normal, while others show underdeveloped secondary sex characteristics and mental retardation can occur. • Also see 48,XXXX and 49,XXXXX individuals…more pronounced symptoms 47,XYY Condition • Phenotypically male, usually over 6 feet tall, sometimes associated with lower intelligence and behavioral problems. The Y Chromosome • Originally thought not to have genes or homology to other chromosomes. – Pseudoautosomal regions (PARs) share homology with X chromosome • Allow pairing during meiosis – The rest of the chromosome is called the male-specific region of the Y (MSY) • Some genes in common with X, and some novel genes • There is at least one very important gene that determin
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