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Module 10

Module 10. Autosomal Traits and Sex Linked Traits. Objectives. Understand the concept of sex linked genes Distinguish between sex-linked and autosomal genes Complete a monohybrid cross using a gene located on the X chromosome. Allele - alternate forms of a given gene. (green or blue eyes)

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Module 10

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  1. Module 10 Autosomal Traits and Sex Linked Traits

  2. Objectives • Understand the concept of sex linked genes • Distinguish between sex-linked and autosomal genes • Complete a monohybrid cross using a gene located on the X chromosome

  3. Allele- alternate forms of a given gene. (green or blue eyes) Independent assortment- random distribution of unlinked genes into gametes. Linked Genes- genes located on the same chromosome tend to be inherited together. The alleles do not assort independently. Sex linked genes- genes located on a sex chromosome. Crossing over- reciprocal exchange of genetic material between non-sister chromatids during meiosis I.

  4. CHROMOSOMES • Sex -chromosomes responsible for determining sex of an individual • Autosomal- chromosome that is not directly involved in determining sex. Female Male XX /XY II III IV Sex -----------Autosomal-----------

  5. Example Phenotypes Ebony Body White Eyes Vestigial Wings W.T.

  6. Genotype Phenotype wt (homozygous) + / + vg / + wt (heterozygous) Review of Nomenclature when referring to Autosomal Traits Autosomal Genes (use + for wt allele) vg / vg mutant

  7. Genotype Phenotype wt (homozygous) + / + vg / + wt (heterozygous) Nomenclature Autosomal Genes (use + for wt allele) vg / vg +_ mutant wt (homo. or het.)

  8. The Law of Independent assortment “Each pair of alleles segregates into gametes independently” (Campbell) For examples: AaBb will segregate and form 4 different gametes: AB, Ab, aB, and ab.

  9. Autosomal Genes vs. Sex Linked Genes • Genes located on Autosomal chromosomes are Autosomal Genes. • Genes that are Sex-linked are located on the X or Y chromosome. • Results from a cross using a sex-linked gene will be much different from a cross using an Autosomal Gene.

  10. Sex-Linked Genes • When a gene is located on the X or the Y chromosome, it is considered Sex-linked • Genes located on the X chromosome are present in both male and females • Genes located on the Y chromosomes are only present in males

  11. Example Monohybrid Cross- Sex Linkage • The gene for eye color is located on the X chromosome. • “W” shows a white phenotype (red is wt) • Cross 1: X+Y X XWXW wild-type male white eye female • Cross 2: XWY X X+X+ white eye male wild-type female

  12. Notice that the Nomenclature for Sex Linked Traits is different than for Autosomal Traits Sex Linked Genes- superscript letter denoting genotype must be attached to respective sex chromosome. Example below is for white eye color. Genotype Phenotype X+X+ X+XW XWXW X+Y XWY wild-type female wild-type female White eye female wild-typemale White eye male

  13. Sex linked genes Example Cross A: Genotype P: X+Y x XWXW (male WT) (female white eyes) gametes: X+,Y XW Genotype F1: XWY X+XW Phenotype F1: Male Female white eyes wild-type eyes

  14. F1 Cross with Progeny from Sex-linked Parental Cross A F1xF1: XWY X X+XW gametes: XW , Y X+ , XWF2 genotypes: X+XW XWXW X+Y XWY

  15. What is the Phenotypic ratio for the F2 Progeny for the Sex-linked Cross A?EXPECTED RESULT = 1:1:1:1 female red eyes (wt) female white eyes male red eyes (wt) male white eyes

  16. Summary of the Sex Linked Cross A wt male X+Y X+, Y Phenotype: Genotype: Gametes: white eyes female XWXW XW P1: Phenotype wt female (carrier) white eyes male Genotype X+XW XWY F1: F1 X F1: white eyes male wild-type female Genotype: XWY X+XW Gametes: XW, Y X+, XW

  17. Continued: Sex Linked for Cross A Results of F1 X F1: Male X+Y XWY Female X+XW XWXW F2: Phenotype ratio: 1:1:1:1 25% female wt (red eyes) 25% female mutant (white eyes) 25% male wt (red eyes) 25% male mutant (red eyes)

  18. Sex-linked Crosses • First, you must perform the F1 mating for the two sex-linked crosses described above. See handout on how to perform the crosses. • For your genetics problem set 2, YOU will follow the same steps to predict the genotypic and phenotypic ratios for Cross B. • Cross B: XWY X X+X+ white eye male wild-type female • Perform Assignment V in Fly Lab On-line, • A complete assignment for genetics problem set B will be your handwritten predictions for Sex-linked Crosses 1 and 2 performed in lab and your data generated from fly lab.

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