Ms. Pender
IS-2
Spring 2013
TOC#_____
Name:_____________________
Period_____________
SEX-LINKED PROBLEMS
In sex-linked inheritance, alleles on sex chromosomes are inherited in predictable patterns. For
example, in Drosophila, the common fruit fly, the locus for eye color is located on the X
chromosome. The allele for red eye color, which is normal in wild flies, is dominant to the mutant
allele for white eyes.
As females have two chromosomes X, they might be homozygous or heterozygous for either allele.
Males, who carry only one X chromosome, are always heterozygous. They carry only one X
chromosome inherited from their mother, and it determines their eye color.
In the below example, homozygous red eyed females (RR) mate with heterozygous white eyed males
(w-). In the offspring, all the daughters are red eyed heterozygotes (Rw) and all sons are red eyed
heterozygotes (R-).
In the right hand, homozygous white eyed females (ww) mate with heterozygous red eyed males
(R).
In the offspring, all the daughters are red eyed heterozygotes (Rw) and all sons are white eyed
heterozygotes (w-).
1)
2)
Give the phenotypes for the following fruit flies;
A)
XRXR
D)
XRY
B)
XRXr
E)
XrY
C)
XrXr
Give the genotypes of the following individuals;
A) Red eye female
D) White eye male
B) Carrier female
E) Afflicted male
C) White eye female
3)
F) Red eye male
Determine the gametes for the following organisms.
A)
Carrier female =
D)
Male =
B)
White eye male =
E)
XhXh =
C)
Red eye male =
F)
VvXRXr =
4)
Cross a carrier female fruit fly with a red eye male fruit fly. Give the phenotypic and genotypic
ratios expected in the F1 offspring. Show the Punnett Squares used for the cross.
5)
be;
Cross a carrier female with a white eye male fruit fly. Of 650 offspring observed how many will
A) females with white eyes?
B) males with red eyes?
C) Red eyes?
D) White eyes?
6)
Cross a wild type, true breeding, female with a white eye male. Show the Punnett Squares.
Will any of the F1 have white eyes? If so, male or female?
7)
You observe a cross that has produced 123 fruit flies. You notice that 31 have white eyes.
On further examination you see that all 31 with white eyes are males. Give the phenotypes and
genotypes of the parents that produced these offspring.
8)
A cross produces 220 offspring. On examination you find that 52% of the males and 48% of
the females have the white eye trait. Give the phenotypes and genotypes of the parents that
produced these offspring. Which parent gave the white eye genes to the 52% of the males that have
white eyes. Which parent gave the white eye genes to the 48% of the females that have the white
eyes.
9)
The individuals that are darkened have red-green color blindness. The “b” gene is recessive
which codes for color blindness. The dominant allele, “B” is normal. Solve the pedigree
below.
What is the probability that F3, #4 is a carrier for the color blind trait? _________
If F2, #6 marries and has a son, what are the chances that she could have a son that is color
blind? ____________________