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Set 4.docx

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BIOL 239
Christine Dupont

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Set 4 2 Chromosomes and reproductionmendel didnt have microscopes or any concept of dna chromosomes or genesEarliest indications1667 studies showing semen contains spermatozoa1854 studies with frogs and seaurchins showing union of male and female gametes Equal contribution to males and females1879 observation of threadlike structures chromosomes on the nuclei of salamander cells during cell division3 Chromosomes and reproduction1880advances in microscopic techniquesuse of dyes for differential staining of cytoplasm nucleus and nuclear structures including chromosomesEarly 1990slinking of chromosomes to the mendelian principles of segregation and independent assortmentproposed that each egg or sperm contains only one of each chromosome of a pairchromosomal theory of inheritance4 chromosomal theory of inheritancestates that hereditary information is on genes and that genes are located on chromosomesAlso that egg and sperm contribute equally to the genetic endowment of offspring through their nucleithey still didnt know anything about dna5 chromosomes and reproduction1901the x and y chromosomes determine sex in grasshoppersSoon others confirmed presence of separate sex chromosomes in other species one sex carriers 2 of the same sex chromosomes females and the other carries one of each malesnot true in all speciesPlatypus studies in PNAS and Nature females are XXXXXx2 males are XXXXXYYYYYnot all xs and ys are homologousmost mammals xx female and xy malesin reptiles zw females and zz males6 X and Y chromosomes7 X and Y chromosomesInheritance of sex chromosomes in animals with XX females and XY males8 Sex Determination
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