Download Sex-Linked Traits

Name __________________________________
Period:______
Sex-Linked Traits & Pedigree Tables
Sex- Linked Trait Background Information: We know that sex-linked traits are carried
only on certain chromosomes. The passing of those traits depend on whether or not the X or Y
allele is passed from generation to generation. To observe how genetic traits are passed,
answer the following questions on sex-linked traits.
Use the information below to answer the following questions:
XB - X chromosome with normal dominant allele (not colorblind)
Xb - X chromosome with recessive colorblind allele
Y -Y chromosome (does not contain comparable gene)
XY- Male
XX- Female
1. Write the genotypes for the following phenotypes of red-green colorblindness.
a. normal male _____________
b. normal female carrying no colorblind alleles (Homozygous) _____________
c. colorblind male _____________
d. normal female carrying the colorblind allele (Heterozygous) _____________
e. colorblind female _____________
2. XBXB
x
XbY
a. What proportion/percent of the male children are
colorblind?
b. What proportion/percent of the female children
are colorblind?
3. XBXb
x
XBY
a. What proportion of the male children are
colorblind?
b. What proportion of the female children are
colorblind?
4. What is the probability that a colorblind woman who marries a man with normal
vision will have a colorblind child?
_____________ X _____________
5. A normal-sighted woman (whose father was colorblind)
marries a colorblind man.
_____________ X _____________
a. What is the probability that they will have a son
who is colorblind?
b. What is the probability that they will have a
colorblind daughter?
Using your notes and knowledge of sex-linked traits, answer the following:
6. What is a sex-linked trait?
7. Why must males inherit colorblindness from their mothers?
8. Why is colorblindness more common in males than in females?
Pedigree Background Information: One way of tracking
sex-linked traits is by using a pedigree. If we are able to look
at the pedigree of plants and animals, we can often determine
the chance that offspring from plants and animals will also
inherit those traits.
Use the information below to answer the following questions:
Circles are Females; Squares are Males
Shaded Circles or Squares indicates that organism has the trait
1. The trait represented by the colored shapes is the dominant trait for no horns (polled).
While scurs is a sex-linked trait, being polled and having horns is not. In the table
below, write the gender as well as the genotype (Use P & p for the alleles) and
phenotype for horns for each animal in the pedigree table.
Are there any homozygous dominant individuals in the pedigree above? How do you
know?
If #7 were bred to #9:
What is the probability of the dominant
trait appearing in offspring?
What is the probability of the recessive
trait appearing in offspring?
If #8 were bred to #10:
What is the probability of the dominant
trait appearing in offspring?
What is the probability of the recessive
trait appearing in offspring?
2. The pedigree seen below is for horns in sheep.
Shaded individuals are horned.
First, determine the probable genotype
of the sheep then, answer the
questions below the table.
How did you determine the genotype of the mother at #7?
Ram #11 was hornless just like his mother. How did the son at #11 get his alleles for
being polled?
What must be the genotypes of the parents of a horned daughter? Explain.
If #13 is bred to a hornless male, what is the probability that their male offspring will be
horned?