Genetics PP6 (Chapter 4 First Half)

Genetics PP6(Chapter 4 First Half)

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Unformatted text preview: Female is heterogametic -- ZW x Male is homogametic -- ZZ Female Male B. Chromosomal Sex Determination B. 3. Ratio determination in Drosophila Drosophila s Other best-studied system besides mammals s Also based on XX females & XY males, but Also uses different determination mechanism different x Determined Determined autosomes by ratio of X chromosomes to ratio B. Chromosomal Sex Determination 3. Ratio determination in Drosophila Drosophila x Determined Determined by ratio of X chromosomes to ratio autosomes autosomes x 2A x 2A 2A (2 each of II, III, and IV) : 2X = female : 1X = male Regardless of whether there is a Y Regardless 4. XO system 4. s System in some insects, e.g. grasshoppers x XX x XO is female (single X) is male Half of sperm have autosomes plus X, half of sperm have autosomes only half 5. Haplodiploidy 5. s System in some insects s Males have only one of each chromosome Males each x 2n (diploid) is female, from fertilized egg x 1n (haploid) is male, from unfertilized egg s Associated with eusociality in Hymenoptera Associated (ants, wasps, bees) (ants, B. Chromosomal Sex Determination 6. Sex chromosome evolution 6. x Starts with autosomal pair Gene mutates to affect sex determtn. Mutated Mutated chromosome loses unrelated genes genes x Has happened multiple times Especially common in plants Sex chromosomes of Papaya vs. Human Y Contains Genes No Genes Sex Chromosome Evolution I. Sex Determination C. Genic Sex Determination 1. Sex set by specific alleles at one or more genes genes s E.g. Most plants x Can Can have male/females plants or male/female tissues in same plant male/female I. Sex Determination D. Environmental Sex Determination 1. Sex set by abiotic environmental cues during development during s E.g. Crocodilians, most turtles x Temperature Temperature of eggs above or below some threshold activates male pathway some x Actual temperature varies with species I. Sex Determination C. Environmental Sex Determination 1. Sex set by abiotic environmental cues s Crocodilians, most turtles 2. Sex set by social environment s Individuals change sex during adult life s E.g. Slipper limpets x Bottom individuals in pile are female x Younger individuals on top are male x Males change to females as they age I. Sex Determination C. Environmental Sex Determination 2. Sex set by social environment 2. s Individuals change sex during adult life s E.g. Coral reef fish x Many species do sex switches x Some species go m-->f, others f-->m x Can take as little as 2 weeks x Triggered by lack of one sex in area, Triggered relative body size, etc. relative Anemone fish: M>F Bluestreak wrasse: F>M Vertebrate Sex Determination...
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This note was uploaded on 09/27/2013 for the course BIO 342 taught by Professor Susanhoffman during the Fall '13 term at Miami University.

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