pedigrees

PedigreesPedigrees

First DecisionFirst Decision

Is it autosomal or Is it autosomal or X-linked inheritance?X-linked inheritance?

Autosomal: both gendersAutosomal: both gendersare equally affected; are equally affected; male-to-male transmission male-to-male transmission observedobserved

If not, propose X-linkageIf not, propose X-linkage

Second DecisionSecond Decision

Is it dominant or recessive?Is it dominant or recessive?

Dominant: trait does not Dominant: trait does not usually skip generations; usually skip generations; each person with at least each person with at least one copy of the dominant one copy of the dominant allele will show the traitallele will show the trait

If not, propose recessiveIf not, propose recessiveinheritance inheritance

Autosomal DominantAutosomal Dominant

• Males and females are Males and females are equally likely to have the equally likely to have the traittrait

• Traits do not skip Traits do not skip generationsgenerations

• The trait is present The trait is present whenever the whenever the corresponding gene is corresponding gene is presentpresent

• Male to male Male to male transmissiontransmission

Autosomal RecessiveAutosomal Recessive

• Males and females are Males and females are equally likely to have equally likely to have the traitthe trait

• Traits often skip Traits often skip generationsgenerations

• Often, both parents of Often, both parents of the offspring who have the offspring who have the trait are the trait are heterozygotesheterozygotes

• Only homozygous Only homozygous individuals have the traitindividuals have the trait

• Traits may appear in Traits may appear in siblings without siblings without appearing in their appearing in their parentsparents

• If a parent has the trait, If a parent has the trait, those offspring who do those offspring who do not have it are not have it are heterozygous carriersheterozygous carriers

X-linked DominantX-linked Dominant• All daughters of a male All daughters of a male

who has the trait will who has the trait will also have the traitalso have the trait

• No male to male No male to male transmissiontransmission

• A female who has the A female who has the trait may or may not trait may or may not pass the gene to her son pass the gene to her son or daughteror daughter

X-linked RecessiveX-linked Recessive

• Trait is more common in Trait is more common in males than femalesmales than females

• All daughters of a male All daughters of a male who has the trait are who has the trait are heterozygous carriersheterozygous carriers

• The son of a female The son of a female carrier has a 50 percent carrier has a 50 percent chance of having the chance of having the traittrait

• No male-to-male No male-to-male transmissiontransmission

• Mothers of male who Mothers of male who have the trait are either have the trait are either heterozygous carriers or heterozygous carriers or homozygous and homozygous and express the traitexpress the trait

• Daughters of female Daughters of female carriers have a 50 carriers have a 50 percent chance of being percent chance of being carrierscarriers

Scenario 2, Page 1-29 of Lab ManualScenario 2, Page 1-29 of Lab Manual

Joseph and Jenny have come to a genetic counselor Joseph and Jenny have come to a genetic counselor to determine their chances of having a child with to determine their chances of having a child with myotonic dystrophy, a degenerative muscular myotonic dystrophy, a degenerative muscular disorder that appears at about 50 years of age and disorder that appears at about 50 years of age and is inherited with the autosomal dominant allele is inherited with the autosomal dominant allele DD. . The autosomal recessive allele The autosomal recessive allele dd does not does not contribute to the development of the disease. Both contribute to the development of the disease. Both Joseph and Jenny are in their thirties and neither Joseph and Jenny are in their thirties and neither shows any signs of the disease at present. Jenny’s shows any signs of the disease at present. Jenny’s grandmother (her father’s mother) has the disease. grandmother (her father’s mother) has the disease. Jenny’s grandmother’s father (Jenny’s great-Jenny’s grandmother’s father (Jenny’s great-grandfather) did not have the disease. There is no grandfather) did not have the disease. There is no history of myotonic dystrophy in Joseph’s family or history of myotonic dystrophy in Joseph’s family or in Jenny’s mother’s or paternal grandfather’s family. in Jenny’s mother’s or paternal grandfather’s family.

a.a. Draw the pedigree that shows the familial Draw the pedigree that shows the familial relationships described in the paragraph above. relationships described in the paragraph above.

b.b. What is the probability that Jenny is a carrier of the What is the probability that Jenny is a carrier of the DD allele? allele?

c.c. What is the probability that Joseph and Jenny will What is the probability that Joseph and Jenny will have a child with myotonic dystrophy?have a child with myotonic dystrophy?

d.d. Out of 3 children born to Joseph and Jenny, what is Out of 3 children born to Joseph and Jenny, what is the probability that 1 will have myotonic dystrophy?the probability that 1 will have myotonic dystrophy?

e.e. Out of 5 children born to Joseph and Jenny, what is Out of 5 children born to Joseph and Jenny, what is the probability that the probability that at least oneat least one will have myotonic will have myotonic dystrophy? dystrophy?


Alkaptonuria is a metabolic disorder that results from Alkaptonuria is a metabolic disorder that results from the autosomal recessive allele the autosomal recessive allele aa. Individuals who do . Individuals who do not have the disease have the dominant allele not have the disease have the dominant allele AA. . Nancy, who does not have alkaptonuria, marries Nancy, who does not have alkaptonuria, marries Norman, who also does not have alkaptonuria. Norman, who also does not have alkaptonuria. Norman’s grandmother (his father’s mother) and Norman’s grandmother (his father’s mother) and Nancy’s uncle (her mother’s brother) have Nancy’s uncle (her mother’s brother) have alkaptonuria. Norman’s grandfather (his father’s alkaptonuria. Norman’s grandfather (his father’s father) does not have the disease and is not a father) does not have the disease and is not a carrier of the alkaptonuria allele. Neither of Nancy’s carrier of the alkaptonuria allele. Neither of Nancy’s maternal grandparents (her mother’s mother and maternal grandparents (her mother’s mother and father) have alkaptonuria. There is no history of father) have alkaptonuria. There is no history of alkaptonuria in Norman’s mother’s family or in alkaptonuria in Norman’s mother’s family or in Nancy’s father’s family. Nancy’s father’s family.

a.a. Draw the pedigree that shows the familial Draw the pedigree that shows the familial relationships described in the paragraph above. relationships described in the paragraph above.

b.b. What is the probability that Nancy is a carrier of the What is the probability that Nancy is a carrier of the aa allele? allele?

c.c. What is the probability that Norman is a carrier of What is the probability that Norman is a carrier of the the aa allele? allele?

d.d. What is the probability that Nancy and Norman’s What is the probability that Nancy and Norman’s first child will have alkaptonuria? first child will have alkaptonuria?

e.e. Out of 5 children born to Nancy and Norman, what Out of 5 children born to Nancy and Norman, what is the probability that 3 will have alkaptonuria?is the probability that 3 will have alkaptonuria?

f.f. Out of 4 children born to Nancy and Norman, what Out of 4 children born to Nancy and Norman, what is the probability that is the probability that at least oneat least one will have will have alkaptonuria?alkaptonuria?


Red-green colorblindness is inherited with Red-green colorblindness is inherited with the X-linked recessive allele the X-linked recessive allele cc. The X-linked . The X-linked dominant allele dominant allele CC codes for full color vision. codes for full color vision. John is colorblind. His wife Jean has full John is colorblind. His wife Jean has full color vision. Both of Jean’s parents and color vision. Both of Jean’s parents and both maternal grandparents (Jean’s both maternal grandparents (Jean’s mother’s parents) have full color vision but mother’s parents) have full color vision but her great grandfather (the father of Jean’s her great grandfather (the father of Jean’s maternal grandmother) is colorblind. There maternal grandmother) is colorblind. There is no history of colorblindness in Jean’s is no history of colorblindness in Jean’s father’s family.father’s family.

a.a. Draw the pedigree that shows the familial Draw the pedigree that shows the familial relationships described in the paragraph relationships described in the paragraph above. above.

b.b. What is the probability that Jean is a carrier What is the probability that Jean is a carrier of the of the cc allele? allele?

c.c. Out of 3 children born to Jean and John, Out of 3 children born to Jean and John, what is the probability that 2 will be what is the probability that 2 will be colorblind sons? colorblind sons?

d.d. Out of 4 children born to Jean and John, Out of 4 children born to Jean and John, what is the probability that what is the probability that at least oneat least one will will be a colorblind daughter?be a colorblind daughter?

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