handout 1.20.11 - 1 Parental Gametes or individuals that...

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1 1/20/11 1. Parental: Gametes or individuals that are like the parents with respect to their chromosomes, genotypes, and/or phenotypes 2. Recombinant: Gametes or individuals that are unlike the parents in terms of their chromosomes, genotypes, and/or phenotypes 3. Recombination frequency (RF): Proportion of recombinant gametes or progeny due to crossover --------------------------------------------------------------------------------------------------------------------------------------- SEX DETERMINATION IN DIFFERENT GROUPS System Group Sexes Discussion XY, Y determination Mammals XY heterogametic males Presence of Y ensures maleness XX homogametic females XY, A/X ratio Fruit flies XY heterogametic males Ratio of autosomes to X chromosomes XX homogametic females determines sexes ZW Birds, ZW heterogametic females Reverse situation of mammals, with Z butterflies ZZ homogametic males and W corresponding to X and Y X0 Grasshoppers X0 males ( 2n =23) Heterogametic males have only 1 sex XX females ( 2n = 24) chromosome as Y completely lost Haplodiploidy Bees, ants, Haploid males Males develop from unfertilized eggs wasps Diploid females Single genes Many plants, Two different mating types 2 alleles at 1 gene encode for different unicellular sexes eukaryotes, fungi Environmental (e.g., Many reptiles Hi temperatures lead to males One of many possibilities (see Fig. 7- temperature- Low temperatures to females 18) dependent) --------------------------------------------------------------------------------------------------------------------------------------- LINKAGE Genes linked to: A. Extranuclear DNA (e.g., mtDNA and cpDNA) B. Nuclear DNA 1. X chromosome (sex linked) 2. Y chromosome (e.g., holandric)) 3. Autosomal linkage Rule, not exception 30000 protein coding genes --------------------------------- = 1300 genes/chromosome (ignoring Y) 22 autosomes + X --------------------------------------------------------------------------------------------------------------------------------------- A. UNLINKED AUTOSOMAL GENES, INDEPENDENT ASSORTMENT Fruit flies wings body vg+ - full e+ - gray
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2 vg vestigial e ebony Progeny genotypes Abbreviated genotypes Phenotypes 0.25 vg+ vg e+ e 0.25 vg+ e+ 0.25 full, gray 0.25 vg+ vg e e 0.25 vg+ e 0.25 full, ebony 0.25 vg vg e+ e 0.25 vg e+ 0.25 vestigial, gray
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