Autosomal Traits and Sex Linked Traits 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) 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.

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

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

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

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

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.

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.

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

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

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 White eye female wild-type male White eye male

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

F1xF1: XWY X X+XW F1 Cross with Progeny from Sex-linked Parental Cross A F1xF1: XWY X X+XW gametes: XW , Y X+ , XW   F2 genotypes: X+XW XWXW X+Y XWY XW Y X+ X+XW X+Y XWXW XWY

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

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

Continued: Sex Linked for Cross A Results of F1 X F1: Female X+XW XW XW Male X+Y XWY 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)

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.