Download Workhseet Key

Name: _________________________________
Sex linked traits and multiple allele problems
Use the following information to help with numbers 1-6. Circle the
best answer.
In humans, the gene for normal color vision (C), is dominant to the
gene for red-green colorblindness. This trait is sex-linked.
1.The parents of a color-blind daughter could have which of the
following genotypes?
A. XCXc and XCY B. XcXc and XCY C. XCXc and XcY
D. XCXC and XcY
2. A heterozygous female marries a color-blind male.The chance of having a colorblind son is
A. 50%
B. 25%
C. 100% D. 0%
3. Both a man and his wife are color blind. The chance that their first child will be a son with
normal vison is…
A. 50%
B. 25%
C. 100%
D. 0%
4. A female who is homozygous for normal vision marries a color-blind male. The chance
that a daughter they produce will be color-blind is…
A. 50%
B. 25%
C. 100%
D. 0%
5. A girl with normal vision has a color-blind father. If the girl marries a color-blind
male, the chance of their first child being a color blind son is…
A. 50%
B. 25%
C. 100%
D. 0%
6. A color-blind female marries a normal vision male. The expected phenotypic ratio among
their offspring is…
A. ½ daughters with normal vision : ½ sons with normal vision
B. ½ color-blind daughters : ½ color-blind sons
C. ½ color-blind daughters : ½ sons with normal vision
D. ½ daughters with normal vision : ½ color-blind sons
7.-15. Indicate whether each of the following statements is TRUE or FALSE. If the statement
is false, correct the bold face underline phrase in a way so to make it true.
In fruit flies, the gene for red eye color, (R), is dominant to the gene for white eye color, (r).
The trait is sex-linked. A red-eyed male was bred with a heterozygous red-eyed female.
The setup: XRY x XRXr
7. The gene for eye color is carried on the X chromosome
TRUE: Sex linked traits, by definition, are carried on the X sex chromosome
8. The male’s genotype is XRYr
FALSE: The Y chromosome does not carry any form of the color blind gene at all
The setup: XRY x XRXr
9. The female’s genotype is XRXr
TRUE: Heterozygous means she will have one of each allele on both of her X chromosomes.
10. Half the gametes produced by the female should contain Xr
TRUE: After meiosis, there is a 50% chance her eggs will have the X chromosome carrying
the white allele.
11. All the gametes produced by the male should contain Yr
FALSE: None of the gametes will have Yr (see explanation for #8)
12. Of the offspring produced, all females are expected to have red eyes.
TRUE: In order for any females to have white eye, they would have to inherit a white allele
from the father. He does not have one to give.
13. Of the the offspring produced, all males are expected to have white eyes.
FALSE: You would expect 50% of the males to have white eyes and 50% to have red eyes.
14. Red-eyed male offspring must have the genotype XrY
FALSE: White eyed males would have the genotype XrY
15. Female offspring produced from this cross could have the genotype XrXr
FALSE: The father does not have the white allele do give.
16. – 21. The diagram below is called a PEDIGREE. Pedigrees are used to track traits down through a series of
generations and can be useful in a number of different ways. This pedigree shows how the trait of color
blindness is carried down through three generations. You need to know that color blindness is a recessive, sexlinked trait.
Each symbol is a person; circles are females and squares are male. Persons 1 and 2 are the original
parents. Marriages are indicated by striped lines and children are shown by solid bars. If a symbol is shaded, the
person is color blind. If a person is unshaded, they have normal vison (but could be a carrier of the color blind
allele). Use this pedigree to answer questions 16 – 21. Use (C) for normal vison and (c) for colorblindness.
16. The genotype of Person 1: XcY
17. The genotype of Person 2 XCXc
18. The genotype of Person 10: XcXc
19. The genotype of Person 14: XCY
20. Can you tell with certainty what the genotype of Person
6 will be? Explain.
Not really. She could be a homozygous or heterozygous for
colorblindness given what you know about her children
(13,14, and 15)
21. The pedigree shows Person 12 as being unshaded. Is
this correct? Explain.
Person 12 ( a son of parents 3 an 4) will be color blind.
Either of mom’s X chromosomes will have have the color
blind gene linked to it.
Traits with more than two forms
22.- 28. Indicate whether each of the following statements is TRUE or FALSE. If the statement is false, correct
the bold face underline phrase in a way so to make it true.
Suppose that when Vincent gets to Titan he finds creatures with three genes that control hair
color. The gene for green hair, (G), is dominant to both the gene for purple hair, (P), and the
gene for orange hair, (O). The gene for purple hair is also dominant to the gene for orange hair.
22. A creature with orange hair must have the genotype OO.
TRUE: Any other combination of alleles would result in either purple or green hair.
23. All creatures with purple hair must be have the genotype, PP.
FALSE: You could still have purple hair with the genotype of PO.
24. All creatures with green hair are either GG or GO.
FALSE: You could be GP and still have green hair because Green is dominant to purple and orange hair.
25. All offspring produced by two orange – haired parents are expected to have orange hair.
TRUE: Two orange-haired parents have nothing but orange alleles to pass down.
26. If two green-haired parents produce an offspring that has orange hair, then each parent must have an O
allele.
TRUE: The only way an orange haired offspring can occur is if it receives an orange allele from each parent.
27. If a purple-haired parent and an orange haired parent produce all purple-haired offspring, then the purplehaired parent is most probably heterozygous.
FALSE: The purple haired parent is most likely homozygous for the purple trait. If it were heterozygous, you
would expect some of the offspring to be orange
28. All the offspring produced by two green-haired creatures always are expected to have green hair.
FALSE: Without knowing the specific genotypes of the parents, you cannot make that assumption. For example, one or
both parents could be heterozygous and result in purple or orange haired offspring.
29. A man has type A blood and his wife has type B blood. A physician types the blood of their four
children and is amazed to find one of each of the four blood types among them. Explain how this
could happen by telling me the genotypes of the parents and their four children.
The only way that each of the four blood types could be expressed in their children, type A,
type B, type AB and type O, is if the parents are: AO x BO.
30. Hemophilia is a sex-linked, recessive trait. A man, who is a hemophiliac, and a woman, who is a carrier of
the condition, want to have children. Although there are effective treatments for this disease,
they are still concerned about having children that must deal with this life long illness. How
would you counsel them? Your explanation can be in the form of a Punnett square that shows
the probable outcomes their children would show.
Parents:
h
X Y
x
H h
X X
X
Xh
XHXh
Y
X Y
Xh
XhXh
XhY
H
H
Based on the Punnett square, you would
tell them that they have a 50% chance of
having a child with hemophilia.