Chapter 4.7: Sex-Linked and Sexually Dimorphic Traits in Humans

Question 1

What type of linked trait would show this in a pedigree:  One-half the sons and one-half the daughters, of an affected female will be affected?

Answer 1

X-Linked Dominant Trait

Question 2

What type of linked trait would show this in a pedigree:  All the daughters but none of the sons of an affected male will be affected?

Answer 2

X-Linked Dominant Trait

Question 3

What do sex-influenced traits?

Answer 3

o Sex-influenced traits show up in both sexes, but expression of such traits may differ between the two sexes because of hormonal differences

Question 4

What type of linked trait would show this in a pedigree:  The trait often skips a generation as the mutation passes from grandfather through a carrier daughter to grandson?

Answer 4

X-Linked Recessive Trait

Question 5

What criterion is most useful for distinguishing an X-linked dominant from an autosomal dominant trait?

Answer 5

 All the daughters but none of the sons of an affected male will be affected

Question 6

What is X-inactivation?

Answer 6

o Almost all genes on the inactivated X chromosome are turned off, so no gene product can be made

Question 7

What are ways to recognize an X-Linked Recessive Trait in a pedigree? (5)

Answer 7

 The trait appears in more males than females because a female must receive two copies of the rare defective allele to display the phenotype, where as a hemizygous male with only one copy will show it
 The mutation will never pass from father to son because sons receive only a Y chromosome from their father
 An affected male passes the X-linked mutation to all his daughter, who are thus carriers. One-half of the sons of these carrier females will inherit the defective allele and thus the trait
 The trait often skips a generation as the mutation passes from grandfather through a carrier daughter to grandson
 The trait can appear in successive generations when a sister of an affected male is a carrier. If she is, one-half of her sons will be affected

Question 8

What show up in both sexes, but expression of such traits may differ between the two sexes because of hormonal differences

Answer 8

sex-influenced traits

Question 9

What do sex-limited traits affect?

Answer 9

o Sex-limited traits affect a structure or process that is found in one sex but not the other

Question 10

What type of linked trait would show this in a pedigree:  More females than males show the aberrant trait?

Answer 10

X-Linked Dominant Trait

Question 11

What is a Barr body?

Answer 11

 Two weeks after fertilization, when a XX human embryo is composed of only 500-1000 cells each cell chooses one X chromosome at random to condense into a so-called Barr body and thereby inactivate it

Question 12

What type of linked trait would show this in a pedigree:  Not only do females not exhibit the trait, they also cannot transmit it?

Answer 12

Y-Linked Trait

Question 13

What are ways to recognize an Y-Linked Trait in a pedigree?

Answer 13

 The trait is seen only in males
 All male descendants of an affected man will exhibit the trait
 Not only do females not exhibit the trait, they also cannot transmit it

Question 14

What affects a structure or process that is found in one sex but not the other

Answer 14

sex-limited traits

Question 15

What type of linked trait would show this in a pedigree:  The mutation will never pass from father to son because sons receive only a Y chromosome from their father?

Answer 15

X-Linked Recessive Trait

Question 16

What type of linked trait would show this in a pedigree:  An affected male passes the X-linked mutation to all his daughter, who are thus carriers. One-half of the sons of these carrier females will inherit the defective allele and thus the trait?

Answer 16

X-Linked Recessive Trait

Question 17

What type of linked trait would show this in a pedigree:  The trait is seen in every generation because it is dominant?

Answer 17

X-Linked Dominant Trait

Question 18

What type of linked trait would show this in a pedigree:  For incompletely dominant X-linked traits, carrier females may show the trait in less extreme form than males with the defective allele?

Answer 18

X-Linked Dominant Trait

Question 19

What type of linked trait would show this in a pedigree:  The trait can appear in successive generations when a sister of an affected male is a carrier. If she is, one-half of her sons will be affected?

Answer 19

X-Linked Recessive Trait

Question 20

What type of linked trait would show this in a pedigree:  The trait is seen only in males?

Answer 20

Y-Linked Trait

Question 21

What is dosage compensation?

Answer 21

o The XX and XY system of sex determination presents human cells with a curious problem that requires a solution called dosage compensation

Question 22

What are ways to recognize an X-Linked Dominant Trait in a pedigree?

Answer 22

 More females than males show the aberrant trait
 The trait is seen in every generation because it is dominant
 All the daughters but none of the sons of an affected male will be affected. This criterion is most useful for distinguishing an X-linked dominant from an autosomal dominant trait
 One-half the sons and one-half the daughters, of an affected female will be affected
 For incompletely dominant X-linked traits, carrier females may show the trait in less extreme form than males with the defective allele

Question 23

What type of linked trait would show this in a pedigree:  All male descendants of an affected man will exhibit the trait?

Answer 23

Y-Linked Trait

Question 24

What type of linked trait would show this in a pedigree:  The trait appears in more males than females because a female must receive two copies of the rare defective allele to display the phenotype, where as a hemizygous male with only one copy will show it?

Answer 24

X-Linked Recessive Trait