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13. Mendelian Genetics

Sex-Linked Inheritance

13. Mendelian Genetics

Sex-Linked Inheritance

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Sex-Linked Inheritance

Jason Amores Sumpter

X-Linked Inheritance

Jason Amores Sumpter

X-Linked Recessive Disorder: Hemophilia Inheritance

Jason Amores Sumpter

X-Linked Recessive Pedigrees

Jason Amores Sumpter

Sex-Linked Inheritance Example 1

Jason Amores Sumpter

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Sex Linked Traits: Baldness and Hemophilia

Y-Linked Traits in a Pedigree

X Linked Inheritance Explained

Inheritance of X-Linked Genes

Professor Dave Explains

Punnett Squares and Sex-Linked Traits

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Practice this topic

Multiple Choice

Wild type fruit flies have red eyes. A white-eyed female fly is crossed with a red-eyed male fly. All of the females from the cross are red-eyed and all of the males, white-eyed. What type of inheritance pattern is this?

Has a video solution.

Multiple Choice

When Thomas Hunt Morgan crossed red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

Has a video solution.

The following pedigree is for the X-linked-recessive trait for color blindness. Using XN for the normal allele and Xn for the color blindness allele, fill in the top half of the boxes/circles with the genotype. Also, fill in the bottom half of the boxes/circles with the phenotype (Normal vision or color blind). If it is impossible to know for certain a specific allele in the genotype, then place a '?' to represent the allele that is in question.

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Multiple Choice

What is the probability that a human male will inherit an X-linked recessive allele from his father?

Multiple Choice

Which of the following results of Thomas Hunt Morgan's experiments with white-eyed mutant flies was unexpected in light of Mendelian genetics?

Multiple Choice

For an X-linked trait, it is the contribution of __________ that determines whether a son will display the trait.

Multiple Choice

If a woman is heterozygous for a recessive sex-linked allele and her husband has the dominant allele, which one of the following is true about the probabilities for their children?

Multiple Choice

In werewolves (hypothetically), the pointy ear allele (P) is dominant over the round ear allele (p). The gene for ear shape is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

Multiple Choice

A woman is red-green color-blind. What can we conclude, if anything, about her father?

Multiple Choice

A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind?

Multiple Choice

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

Multiple Choice

Hemophilia is an X-linked disorder. The daughter of a father with hemophilia and a carrier mother has a __________ probability of having hemophilia.

Multiple Choice

Consider a woman who is a carrier of a recessive X-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Multiple Choice

In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome?

Multiple Choice

X-linked genes differ from Y-linked genes in which of the following ways?

Textbook Question

A man with hemophilia (a recessive, sex-linked condition) has a daughter without the condition. She marries a man who does not have hemophilia. What is the probability that their daughter will have hemophilia? Their son? If they have four sons, what is the probability that all will be affected?

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Textbook Question

Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently unaffected parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.

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Textbook Question

A woman is a carrier of the X-linked recessive color blindness gene. She has children with a man with normal color vision. Which of the following is true of their offspring? a. All the males will be color blind; b. All the females will be carriers; c. Half the females will be color blind; d. Half the males will be color blind.

Has a video solution.

Textbook Question

A fruit fly with a gray body and red eyes (genotype BbPp) is mated with a fly having a black body and purple eyes (genotype bbpp). What ratio of offspring would you expect if the body-color and eye-color genes are on different chromosomes (unlinked)? When this mating is actually carried out, most of the offspring look like the parents, but 3% have a gray body and purple eyes, and 3% have a black body and red eyes. Are these genes linked or unlinked? What is the recombination frequency?

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Textbook Question

A series of matings shows that the recombination frequency between the black-body gene and the gene for dumpy (shortened) wings is 36%. The recombination frequency between purple eyes and dumpy wings is 41%. What is the sequence of these three genes on the chromosome?

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Textbook Question

The pedigree in the figure below illustrates the inheritance of a sex-linked recessive trait. What is the genotype of individual II-5?

a. XHXH; b. XHXh; c. XhXh; d. XHY; e. XhY

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Textbook Question

As a genetic counselor, you advise couples about the possibility of genetic disease in their offspring. Today you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked recessive condition. His ﬁancée, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted. The sister of this man is planning to marry his fiancée's brother. How would you advise this second couple?

Has a video solution.

Textbook Question

As a genetic counselor, you advise couples about the possibility of genetic disease in their offspring. Today you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked recessive condition. His ﬁancée, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted. How would you advise this couple?

Has a video solution.

Textbook Question

A couple are both phenotypically normal, but their son suffers from hemophilia, a sex-linked recessive disorder. What fraction of their children are likely to suffer from hemophilia? What fraction are likely to be carriers?

Has a video solution.

Textbook Question

Why do more men than women have colorblindness?

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Textbook Question

Two mothers give birth to sons at the same time in a busy hospital. The son of couple 1 is afflicted with hemophilia A, which is a recessive X-linked disease. Neither parent has the disease. Couple 2 has a normal son even though the father has hemophilia A. The two couples sue the hospital in court, claiming that a careless staff member swapped their babies at birth. You appear in court as an expert witness. What do you tell the jury? Make a diagram that you can submit to the jury.

Has a video solution.

Textbook Question

Heather was surprised to discover she suffered from red-green colorblindness. She told her biology professor, who said, 'Your father is colorblind, too, right?' How did her professor know this? Why did her professor not say the same thing to the colorblind males in the class?

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Textbook Question

Recall that hemophilia is an X-linked recessive disease. If a woman with hemophilia had children with a man without hemophilia, what is the chance that their first child will have the disease? What is the chance that their first child will be a carrier?

Has a video solution.

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