LS4 Lect_3

LS4 Lect_3 - Drosophila melanogaster • Short life cycle...

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Unformatted text preview: Drosophila melanogaster • Short life cycle - 12 days • Many progeny • Easy to grow in laboratories Calvin Bridges, an undergraduate dishwasher, discovered a white-eyed fly (normal flies have red eyes) in one of the fly bottles he was about to wash Karyotypes can be produced by cu0ng micrograph images of stained chromosomes and arranging them in matched pairs Human karyotype (male or female?) Autosomes – pairs of nonsex chromosomes Sex chromosomes and autosomes are arranged in homologous pairs Note 22 pairs of autosomes and 1 pair of sex chromosomes Karyotype of human; 2n = 46 23 pairs X w+ Y X w Y X w X w+ X w X w Y X w+ X w+ X w X w+ Y X w ˁ x X w+ ˂ X w+ ˁ x X w+ ˂ Y X w Y X w X w Y X w+ Y X w+ X w+ X w X w+ Y X w+ X w+ X w+ X w+ Y X w X w X w X w Y X w X w+ X w X w Y 4 red ˁ x white ˂ white ˁ + red ˂ white ˁ x red ˂ red ˁ + red ˂ ˁ ˂ ˁ ˂ ˁ ˂ ˁ ˂ 5 ˁ ˂ ˂ ˁ BRIDGES red ˁ x white ˂ white ˁ + red ˂ ; but also 1/1000 white ˂ and red ˁ In flies, XXX is lethal; XXY is a female; XO is a male; YO is lethal. n = the number of chromosomes ploidy haploid genome = 1n example: vegetative life cycle of some yeast and slime molds diploid genome = 2n example: most animals tetraploid genome = 4n example: Xenopus Trisomy: an individual carries one extra chromosome (2n + 1) most trisomies in humans are lethal. Down syndrome (47, + 21) is an example of viable trisomy in humans Aneuploid: a numerical change in part of the genome Example: Non‐disjunc9on in humans, can occur at all of the chromosomes at a low frequency. Trisomy Trisomy 21 21 ; Down syndrome. 47 chromosomes are present instead of ; Down syndrome. 47 chromosomes are present instead of 46 from duplica9on of chromosome #21. Extra level of gene product 46 from duplica9on of chromosome #21. Extra level of gene product causes phenotype. causes phenotype. Trisomy Trisomy 21 appears to be related to maternal 21 appears to be related to maternal age, amniocentesis suggested....
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LS4 Lect_3 - Drosophila melanogaster • Short life cycle...

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