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© 2012 W. H. Freeman and Company

CHAPTER 6p 139 - 164

[p 127 – 151]

Study Unit 5

Pedigree Analysis, Applications, and Genetic Testing

Study Unit 5

Pedigree Analysis, Applications, and Genetic Testing

Benjamin A. PierceGENETICS

A Conceptual Approach

Pedigree analysisAutosomal Recessive

Alleles: Genotypes:

A = normal a = mutant AA = normalAa = pt normal, carrier

aa = affected

Autosomal Recessive inheritance

Autosomal Dominant

Alleles: Genotypes:

A = mutant a = normal AA = affectedAa = affected

aa = normal

X-linked recessive

Alleles: Genotypes:

XA = normal Xa = mutant XAXA = normal XAY = normalXAXa = pt normal, carrier

XaXa = affected XaY = affected

X-linked dominant

Alleles: Genotypes:

XA = mutant Xa = normal XAXA = affected XAY = affectedXAXa = affected

XaXa = normal XaY = normal

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Y-linked

Alleles: Genotypes:

Ya’ = mutant Ya = normal XYa’ = affected

XYa = normal

You are studying cystic fibrosis (CF). While looking at apedigree you notice that the CF phenotype is not presentin a set of parents, but one out of their five children hasCF. What can you conclude about CF?

A. The trait is X-linked.

B. The trait is autosomal dominant.

C. The trait is autosomal recessive.

D. We do not have enough data to conclude anything.

The trait

is X

-linke

d.

The trait

is a

utoso

mal d

...

The trait

is a

utoso

mal r

ec...

We d

o not h

ave e

nough ..

.

3%

15%

80%

2%

In studying an X-linked dominant trait, you examine afamily with seven children. None of the three sons hasthe trait and all four daughters have the trait. What is alikely conclusion about the parents?

A. The mother has the X-linked dominant trait.

B. Both mother and father have the X-linked dominant trait.

C. This mutation likely arose during meiosis of either parent.

D. The father has the X-linked dominant

trait.

E. We do not have enough data to

conclude anything.The m

other

has

the

X-lin

k..

Both m

other

and

fath

er ..

.

This m

utatio

n like

ly a

ros..

.

The fath

er has

the X

-link.

.

We

do not h

ave e

nough

...

9% 6%2%

81%

1%

Example problem:For each of the following pedigrees, determine the most likely mode of inheritance. Assume that the trait is fully penetrant. Give a reason for your answer and assign genotypes to individuals as indicated below each pedigree.

I 1 2 3 4 5 6

II 1 2 3 4 5 6 7 8

III 1 2 3 4 5 6 7 8 9

Most likely mode of inheritance: _______________________________________

Reason for your answer: _____________________________________________

Please provide genotypes for: I-4: __________ II-2:__________ III-9: ________

A.

I

II

III

Most likely mode of inheritance: _______________________________________

Reason for your answer: _____________________________________________

Please provide genotypes for: I-1: __________ II-3:__________

B.

1 2 3 4

1 2 3 4 5

1 2 3

I

II

III

C.

1 2

4

1 2 3 4 5

1 2 3

6 7

5 6

Most likely mode of inheritance: _______________________________________

Reason for your answer: _____________________________________________

Please provide genotypes for: I-1: __________ II-3:__________ II-5: ________

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D.

Most likely mode of inheritance: _______________________________________

Reason for your answer: _____________________________________________

Please provide genotypes for: II-1: ________ IV-1:_________ IV-2: ________

E.

Most likely mode of inheritance: _______________________________________

Reason for your answer: _____________________________________________

Please provide genotypes for: I-1: ________ II-2:_________ II-5: ________

Class notes:

Typically, during the process of in vitro fertilizationseveral eggs are fertilized. If two of these eggs wereallowed to develop in the mother, then what kind oftwins would result?

A. monozygotic

B. dizygotic

C. conjoined

D. Any of the above.

monozy

gotic

dizyg

otic

conjo

ined

Any o

f the a

bove.

3% 5%1%

91%

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The concordance values for cancer amongstmonozygotic and dizygotic twins are 12% and 15%,respectively. What do these data suggest aboutcancer?

A. The occurrence of cancer is mostly linked to genetic factors.

B. The occurrence of cancer is mostly linked to environmental

factors.

C. The occurrence of cancer is

linked equally to both genetic and environmental factors.

D. Such low values make interpretation difficult

The occ

urrence

of c

ancer ..

The occ

urrence

of c

ance...

The occ

urrence

of c

ancer ..

Such lo

w v

alues

make in

...

6% 5%

18%

70%

The concordance rate of epilepsy is 59% formonozygotic and 19% for dizygotic twins. Thisdemonstrates that:

A. it does not have an environmental component.

B. it is not caused by a single gene.

C. it is not 100% penetrant.

D. it has a strong genetic component.

E. All of the above.

it d

oes not h

ave an e

nv...

it is

not c

aused b

y a s

ingl..

.

it is

not 1

00% p

enetrant.

it h

as a

stro

ng geneti

c c.

..

All

of the a

bove.

0% 0% 0%0%0%

Lucy is 16 weeks pregnant and undergoes maternalserum screening to measure her maternal alphafetoprotein levels (AFP). Her AFP level is several timeshigher that normal levels. For which of the followingdisorders should Lucy be offered additional testing?

A. Trisomy 21, a chromosome abnormality

B. Sickle-cell disease, an autosomal recessive disorder

C. Spina bifida, a neural tube defect

D. Hemophila A, a sex-linked recessive disorder

E. Lucy does not need additional testing for any disorder.

Trisom

y 21,

a chro

mos

o..

Sickl

e-ce

ll dise

ase, a

n au...

Spina b

ifida,

a n

eura

l tu..

Hem

ophila A

, a sex-

linked

...

Lucy

doe

s not n

eed a

ddi..

.

15%

6% 5%4%

70%

Several members of a family have a very rare form ofhearing disorder. You construct the followingpedigree. The most likely mode of inheritance is

A. autosomal dominant since the trait does not skip generations.

B. X-linked dominant since an affected woman can have both affected

sons and affected daughters.

C. autosomal recessive, where all the unaffected individuals are

heterozygous for the condition.

D. mitochondrial since affected females pass the condition on to all

their children and affected males do not.

E. The mode of inheritance in the above pedigree does not fit any of

the previous mentioned modes in inheritance.

A. B. C. D. E.

15%

42%

4%

31%

8%

Semester test 2

• Wednesday 15 October

• SU4 – end of todays lecture