Module 6 Lesson 7 - 5

Self-Check

1. In a cross between a white-eyed female fruit fly and red-eyed male, what percent of the female offspring will have white eyes? (White eyes are X-linked and recessive.)


2. A female Drosophila of unknown genotype was crossed with a white-eyed male fly of genotype X^wY (w = white eye allele is recessive, w+ = red-eye allele is dominant). Half the male and half the female offspring were red-eyed, and half the male offspring and half the female offspring were white-eyed. What was the genotype of the female fly?


3. In a cross between a pure bred red-eyed female fruit fly and a white-eyed male, what percent of the male offspring will have white eyes? (White eyes are X-linked, recessive.)


4. What is the genotype of a red-eyed, yellow-bodied female fruit fly that is homozygous for the eye colour allele? Red eyes (w+) and tan bodies (y+) are the dominant alleles. (Both traits are X-chromosome linked. This is a dihybrid genotype.)


5. A white-eyed female fruit fly is crossed with a red-eyed male. Red eyes are dominant and X-linked. What are the expected phenotypes of the offspring?


6. Hemophilia in humans is due to an X-chromosome mutation. What will be the results of mating between a normal (non-carrier) female and a hemophiliac male?


7. A human female carrier who is heterozygous for the recessive sex-linked trait causing red-green colour blindness marries a normal male. What proportion of their male progeny will have red-green colour blindness?



8. Women have sex chromosomes of XX, and men have sex chromosomes of XY.

   1. Which of a man's grandparents could not be the source of any of the genes on his Y-chromosome?
   2. Which of a women's grandparents could not be the source of any of the genes on either of her X-chromosomes?


9. A human female carrier who is heterozygous for the recessive sex-linked trait red colour blindness marries a normal male. What proportion of their female progeny will show the trait?

Diploma Connection

Answer the following questions from a previous Biology 30 Diploma Examination.

Use the following information to answer the next question.

In humans, the allele for normal blood clotting (H) is dominant to the allele for hemophilia (h). The trait is X-linked.

1. A female hemophiliac marries a man who is not a hemophiliac. The row that indicates the probability of this couple having a child that is a hemophiliac and indicates the sex of the child is
   
   

   Row	Probability	Sex of Affected Child
   A.	0.25	male
   B.	0.25	either female or male
   C.	0.50	male
   D.	0.50	either male or female





2. Numerical Response

   A woman who is not a hemophiliac has a father who is a hemophiliac. If this woman marries a man who is a hemophiliac, what is the probability of them having a hemophiliac son?
   
   Answer: ___________
   



Use the following information to answer the next question.

A recessive allele causes Drosophila to have white eyes instead of wild-type eyes. This eye colour gene is known to be X-linked. In a cross between homozygous wild-type females and white-eyed males, all F1 progeny have wild-type eyes.

3. What ratio of wild-type to white-eyed progeny can be expected in each sex if F₁ females are crossed to males of the same genotype as their father?
   
   
   1. Males - 1 : 0; females - 1 : 0
   2. Males - 1 : 1; females - 1 : 0
   3. Males - 0 : 1; females - 1 : 1
   4. Males - 1 : 1; females - 1 : 1



Use the following information to answer the next question.





4. To determine whether this is an X chromosome or an autosome, a researcher would have to determine whether these traits are
   
   
   1. recessive
   2. dominant
   3. passed from male parents to their male offspring
   4. passed from female parents to their male offspring
      
   
   



Use the following information to answer the next question.

Scientists have identified a genetic condition that apparently makes some men prone to impulsive, violent behaviour. A pedigree was drawn highlighting the violent members of a particular family. It appeared from the pedigree that men who displayed this violent behaviour inherited this condition from their mothers, not their fathers. Further evidence showed that this was the mode of inheritance.

-from Richardson, 1993

5. The inheritance pattern described indicates that this condition is
   
   
   1. X-linked
   2. Y-linked
   3. autosomal
   4. codominant


6. A dominant allele, X^E, carried on the X chromosome, causes the formation of faulty tooth enamel, the resulting enamel being either very thin or very hard enamel. The faulty tooth enamel trait will appear in all daughters but no sons if the children have
   
   
   1. a father with normal tooth enamel and a mother with normal tooth enamel
   2. a father with normal tooth enamel and mother with faulty tooth enamel
   3. a father with faulty tooth enamel and a mother with normal tooth enamel
   4. a father with faulty tooth enamel and a mother with faulty tooth enamel



7. Numerical Response

   A dominant allele, X^E, carried on the X chromosome causes the formation of faulty tooth enamel, resulting in either very thin or very hard enamel. A woman heterozygous for faulty tooth enamel marries a man with normal tooth enamel. What is the probability that their first child will be a boy with normal tooth enamel?
   

   Answer: _____________