Bio 1 - First set of laptop notes Linkage in Fruit Flies...

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First set of laptop notes Linkage in Fruit Flies (Drosophila) NOTATION for fruit flies: B = normal gray body (wild type) b = black body V = normal long wing (wild type) v = vestigal (short) wing Wild flies have gray bodies: Completely Harmless |F1 Female: BbVv: Gray, normal wings| |F1 Male: bbVv: vestigial wings | = BbVv, bbvv, Bbvv, bbVv Parental Type Gametes: Combinations present in the parents Recombinants: New combinations Crossing-Over: Two homologous chromosomes undergo synapsis in meiosis. Every tetrad must have atleaset one crossover. However, that does not specify where the crossover must occur. Only in a fraction of a cells will the corssover be between the B locust and b locust. Most of the cells will usually only give out parental type gametes. Only a fraction of a cell will there be a be a crossover that gives a recombinant type. Far apart: the genes are on the chromosme means more opportunites for crossing over. Not so far apart: the genes that are on the chromosome means less opportunities for crossing over. Classes with excess is a parental type. Classes with deficiencies mean recombinant type. AB Ab aB ab ab AaBb Aabb aaBb aabb 26 23 24 27 AB Ab aB ab ab AaBb Aabb aaBb aabb 45 5 4 46 PAR REC REC PAR
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Conclution: Linked AB Ab aB ab ab AaBb Aabb aaBb aabb 5 45 46 4 Rec par par rec P generation was Aabb X aaBB Each P generation is homozygous. Numbers don’t say anything unless the chart is linke.d Sex Determination Mechanisms actually vary Not all organisms have separate sexes Not al organisms with separate sexes have sex chromosomes Sex Chromosomes Humans and Drosophila XX = female XY = male Birds ZZ = male ZW (or sometimes Z0) = female 0 means the W chromosome is absent A sperm may contain either an X or a Y chromosome Every egg cell contains an x chromosome. Female: if the egg is fertilized by an X sperm, the zygote will contain two X chromosomes and the offspring will be female. Male : if the egg is fertilized by a Y sperm, the zygote will contain an XY. Discovery of X-linkage Drosophila Laboratory of Dr. Thomas Hunt Morgan (at Columbia University) Scientists wanted to use animal organisms that had similar advantages to pea plants. Fly with white eyes? Everyone got excited…had to turn it over and look at it from all different angles. It woke up and started flying around. Red-eyed (wild type) females X White-eyed male F1--all red eyed F2--Females all red-eyed males 1:1 white to red Morgan’s hypothesis
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XsuperW = X chromosome with red allele Xsuperw = X chromsome with white alelle Morgan’s test cross F1 females X white-eyed male Offspring (both sexes) 1:1 of red to white X-Linked Genes Required in both sexes Examples: Color-vision (red-green colorblindness) Muscle development (Duchenne muscular dystrophy) Blood clotting (hemophilia A) (Males usually suffer from all of these) Dosage compensation PROBLEM!! How can the expression of these important X-linked genes be equivalent in both sexes?
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Bio 1 - First set of laptop notes Linkage in Fruit Flies...

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