BIOL 202 Lecture Notes - Lecture 3: Y Chromosome, Nondisjunction, Meiosis
Document Summary
Nettie stevens: first person to recognize that differences in chromosomes correspond to physical differences in organisms, used mealworm larvae. Thomas hunt morgan: used drosophila, noticed a white-eyed fruit fly (abnormal from the typical red-eyed fly, sex determination in drosophila. Female: two x"s: sex chromosomes in drosophila. The y chromosome is significantly shrunken and does not carry many genes on it: morgan"s sex-linkage cross: Expected mendelian f1 cross: red (f) x white (m) = all red. Red (f) x red (m) = 3 red: 1 white (males and females) Observed f2 cross: all red (females), 1 red: 1 white (males) White (f) x red (m: autosomal expected f1. All red females, all white males: autosomal expexted f2. 3 red: 1 white: observed f2. 1:1 segregation in both males and females. Morgan"s explanation (hemizygous male only one allele): Calvin bridges (morgan"s student) and the chromosome theory of inheritance: Expected based on chromosomal inheritance: all red (f) and all white (m)
