1. Autosomal Traits and Sex Linked Traits
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
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.

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

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

7. 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.)

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
White eye female
wild-type male
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. 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

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
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

17. 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)

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.